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</div><h2>SL Paper 2</h2><div class="specification">
<p>Consider the following list of organic compounds.</p>
<p> Compound 1: \({\text{C}}{{\text{H}}_{\text{3}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{CH(OH)C}}{{\text{H}}_{\text{3}}}\)</p>
<p> Compound 2: \({\text{C}}{{\text{H}}_{\text{3}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{COC}}{{\text{H}}_{\text{3}}}\)</p>
<p> Compound 3: \({\text{C}}{{\text{H}}_{\text{3}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{OH}}\)</p>
<p> Compound 4: \({\text{C}}{{\text{H}}_{\text{3}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{CHO}}\)</p>
</div>
<div class="specification">
<p>Hydrochloric acid neutralizes sodium hydroxide, forming sodium chloride and water.</p>
<p style="text-align: center;">\({\text{NaOH(aq)}} + {\text{HCl(aq)}} \to {\text{NaCl(aq)}} + {{\text{H}}_{\text{2}}}{\text{O(l)}}\) \(\Delta {H^\Theta } = -57.9{\text{ kJ}}\,{\text{mo}}{{\text{l}}^{ - 1}}\)</p>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Apply IUPAC rules to state the name of compound 1.</p>
<div class="marks">[1]</div>
<div class="question_part_label">a.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>(i) Define the term <em>structural isomers</em>.</p>
<p> </p>
<p> </p>
<p>(ii) Identify the two compounds in the list that are structural isomers of each other.</p>
<div class="marks">[2]</div>
<div class="question_part_label">b.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Determine the organic product formed when each of the compounds is heated under reflux with excess acidified potassium dichromate(VI). If no reaction occurs write NO REACTION in the table.</p>
<p style="text-align: center;"><img src="images/Schermafbeelding_2016-08-23_om_08.41.32.png" alt="N14/4/CHEMI/SP2/ENG/TZ0/07.c"></p>
<div class="marks">[4]</div>
<div class="question_part_label">c.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Explain the mechanism for the substitution reaction of bromoethane with sodium hydroxide. Use curly arrows to represent the movement of electron pairs.</p>
<div class="marks">[4]</div>
<div class="question_part_label">d.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>(i) Define the term <em>standard enthalpy change of reaction</em>, \(\Delta {H^\Theta }\).</p>
<p> </p>
<p> </p>
<p> </p>
<p>(ii) Determine the amount of energy released, in kJ, when \({\text{50.0 c}}{{\text{m}}^{\text{3}}}\) of \({\text{1.00 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}\) sodium hydroxide solution reacts with \({\text{50.0 c}}{{\text{m}}^{\text{3}}}\) of \({\text{1.00 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}\) hydrochloric acid solution.</p>
<p> </p>
<p> </p>
<p> </p>
<p> </p>
<p>(iii) In an experiment, 2.50 g of solid sodium hydroxide was dissolved in \({\text{50.0 c}}{{\text{m}}^{\text{3}}}\) of water. The temperature rose by 13.3 °C. Calculate the standard enthalpy change, in \({\text{kJ}}\,{\text{mo}}{{\text{l}}^{ - 1}}\), for dissolving one mole of solid sodium hydroxide in water.</p>
<p>\[{\text{NaOH(s)}} \to {\text{NaOH(aq)}}\]</p>
<p>(iv) Using relevant data from previous question parts, determine \(\Delta {H^\Theta }\), in \({\text{kJ}}\,{\text{mo}}{{\text{l}}^{ - 1}}\), for the reaction of solid sodium hydroxide with hydrochloric acid.</p>
<p>\[{\text{NaOH(s)}} + {\text{HCl(aq)}} \to {\text{NaCl(aq)}} + {{\text{H}}_{\text{2}}}{\text{O(l)}}\]</p>
<div class="marks">[9]</div>
<div class="question_part_label">e.</div>
</div>
<h2 style="margin-top: 1em">Markscheme</h2>
<div class="question" style="padding-left: 20px;">
<p>butan-2-ol/2-butanol;</p>
<div class="question_part_label">a.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>(i) same <span style="text-decoration: underline;">molecular formula</span> but differ in arrangement of their atoms;</p>
<p><em>Allow “different structures/structural formulas” instead of “different arrangement of atoms”.</em></p>
<p>(ii) (compounds) 2 and 4 / butanone and butanal;</p>
<div class="question_part_label">b.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p><img src="images/Schermafbeelding_2016-08-23_om_08.42.28.png" alt="N14/4/CHEMI/SP2/ENG/TZ0/07.c/M"></p>
<div class="question_part_label">c.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p><img src="images/Schermafbeelding_2016-08-23_om_08.48.46.png" alt="N14/4/CHEMI/SP2/ENG/TZ0/07.d/M"></p>
<p>curly arrow going from lone pair/negative charge on O in \({\text{H}}{{\text{O}}^ - }\) to C;</p>
<p><em>Do not allow curly arrow originating on H in HO<sup>–</sup>.</em></p>
<p>curly arrow showing Br leaving;</p>
<p><em>Accept curly arrow either going from bond between C and Br to Br in bromoethane or in the transition state.</em></p>
<p>representation of transition state showing negative charge, square brackets and partial bonds;</p>
<p><em>Do not penalize if HO and Br are not at 180°</em> <em>to each other.</em></p>
<p><em>Do not award M3 if OH—C bond is represented, but penalise wrong bonding once only.</em></p>
<p>formation of organic product \({\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{OH}}\) <strong>and</strong> \({\text{B}}{{\text{r}}^ - }\);</p>
<p><em>Accept “NaBr / Na<sup>+</sup></em> <em>and Br<sup>–</sup>” as product.</em></p>
<p><em>If candidate writes an S<sub>N</sub>1 mechanism then deduct 1 mark for this, so that it is marked out of </em><strong><em>[3 max]</em></strong><em>.</em></p>
<div class="question_part_label">d.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>(i) heat transferred/absorbed/released/enthalpy/<span style="text-decoration: underline;">potential</span> energy change when 1 mol/molar amounts of reactant(s) react (to form products) <em>/ OWTTE</em>;</p>
<p>under standard conditions / at a pressure 100 kPa/101.3 kPa/1 atm <strong>and</strong> temperature 298 K/25 °C;</p>
<p><em>Award </em><strong><em>[2] </em></strong><em>for difference between standard enthalpies of products and standard enthalpies of reactants / </em>\({H^\Theta }\) <em>(products) – </em>\({H^\Theta }\) <em>(reactants).</em></p>
<p><em>Award </em><strong><em>[2] </em></strong><em>for difference between standard enthalpies of formation of products and standard enthalpies of formation of reactants / </em>\(\Sigma \Delta H_f^\Theta \) <em>(products) – </em>\(\Sigma \Delta H_f^\Theta \) <em>(reactants).</em></p>
<p>(ii) \((1.00 \times 0.0500 = ){\text{ }}0.0500{\text{ (mol)}}\);</p>
<p>\((0.0500 \times 57.9 = ){\text{ }}2.90{\text{ (kJ)}}\);</p>
<p><em>Ignore any negative sign.</em></p>
<p><em>Award </em><strong><em>[2] </em></strong><em>for correct final answer.</em></p>
<p><em>Award </em><strong><em>[1 max] </em></strong><em>for 2900 J.</em></p>
<p>(iii) \(\left( {\frac{{2.50}}{{40.00}} = } \right){\text{ }}0.0625{\text{ (mol NaOH)}}\);</p>
<p>\(0.0500 \times 4.18 \times 13.3 = 2.78{\text{ (kJ)}}/50.0 \times 4.18 \times 13.3 = 2780{\text{ (J)}}\);</p>
<p>\(\left( {\frac{{2.78}}{{0.0625}}} \right) = - 44.5{\text{ }}({\text{kJ}}\,{\text{mo}}{{\text{l}}^{ - 1}})\);</p>
<p><em>Award </em><strong><em>[3] </em></strong><em>for correct final answer.</em></p>
<p><em>Negative sign is necessary for M3.</em></p>
<p><em>Award M2 and M3 if 52</em>.<em>5 g is used to obtain an enthalpy change of –46.7.</em></p>
<p>(iv) –44.5 – 57.9 / correct Hess’s Law cycle (as below) / correct manipulation of equations;</p>
<p><img src="images/Schermafbeelding_2016-08-23_om_09.24.21.png" alt="N14/4/CHEMI/SP2/ENG/TZ0/07.e.iv/M"></p>
<p>–102.4 (kJ);</p>
<p><em>Award </em><strong><em>[2] </em></strong><em>for correct final answer.</em></p>
<div class="question_part_label">e.</div>
</div>
<h2 style="margin-top: 1em">Examiners report</h2>
<div class="question" style="padding-left: 20px;">
<p>Most students scored well on naming the required compound from its formula in Part (a), likewise defining structural isomers and recognising compounds related in the way, required in Part (b), were rarely a challenge. In Part (c) students could usually identify whether compounds underwent oxidation and the products formed, with the most common mistake being to fail to notice that there was excess dichromate(VI) in the case of the primary alcohol. The mechanism required in Part (d) seemed to be known to many, though many candidates continue to lose marks through a lack of precision about the start and finish points of curly arrows. Many students gained at least one mark for the definition standard enthalpy change in the first section of Part (e), though few displayed the precision required for both marks. In the second section quite a few tried to solve the enthalpy problem by calorimetry rather than using the enthalpy of reaction that had been given. Generally speaking the next section, that did require calorimetry, was better done though the calculation of the amount of reagent and using the mass of liquid rather than solid for the heat evolved proved a challenge for some. Many candidates correctly combined their results, sometimes invoking Hess’ Law, in the final section, though many candidates benefited from the application of ECF.</p>
<div class="question_part_label">a.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>Most students scored well on naming the required compound from its formula in Part (a), likewise defining structural isomers and recognising compounds related in the way, required in Part (b), were rarely a challenge. In Part (c) students could usually identify whether compounds underwent oxidation and the products formed, with the most common mistake being to fail to notice that there was excess dichromate(VI) in the case of the primary alcohol. The mechanism required in Part (d) seemed to be known to many, though many candidates continue to lose marks through a lack of precision about the start and finish points of curly arrows. Many students gained at least one mark for the definition standard enthalpy change in the first section of Part (e), though few displayed the precision required for both marks. In the second section quite a few tried to solve the enthalpy problem by calorimetry rather than using the enthalpy of reaction that had been given. Generally speaking the next section, that did require calorimetry, was better done though the calculation of the amount of reagent and using the mass of liquid rather than solid for the heat evolved proved a challenge for some. Many candidates correctly combined their results, sometimes invoking Hess’ Law, in the final section, though many candidates benefited from the application of ECF.</p>
<div class="question_part_label">b.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>Most students scored well on naming the required compound from its formula in Part (a), likewise defining structural isomers and recognising compounds related in the way, required in Part (b), were rarely a challenge. In Part (c) students could usually identify whether compounds underwent oxidation and the products formed, with the most common mistake being to fail to notice that there was excess dichromate(VI) in the case of the primary alcohol. The mechanism required in Part (d) seemed to be known to many, though many candidates continue to lose marks through a lack of precision about the start and finish points of curly arrows. Many students gained at least one mark for the definition standard enthalpy change in the first section of Part (e), though few displayed the precision required for both marks. In the second section quite a few tried to solve the enthalpy problem by calorimetry rather than using the enthalpy of reaction that had been given. Generally speaking the next section, that did require calorimetry, was better done though the calculation of the amount of reagent and using the mass of liquid rather than solid for the heat evolved proved a challenge for some. Many candidates correctly combined their results, sometimes invoking Hess’ Law, in the final section, though many candidates benefited from the application of ECF.</p>
<div class="question_part_label">c.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>Most students scored well on naming the required compound from its formula in Part (a), likewise defining structural isomers and recognising compounds related in the way, required in Part (b), were rarely a challenge. In Part (c) students could usually identify whether compounds underwent oxidation and the products formed, with the most common mistake being to fail to notice that there was excess dichromate(VI) in the case of the primary alcohol. The mechanism required in Part (d) seemed to be known to many, though many candidates continue to lose marks through a lack of precision about the start and finish points of curly arrows. Many students gained at least one mark for the definition standard enthalpy change in the first section of Part (e), though few displayed the precision required for both marks. In the second section quite a few tried to solve the enthalpy problem by calorimetry rather than using the enthalpy of reaction that had been given. Generally speaking the next section, that did require calorimetry, was better done though the calculation of the amount of reagent and using the mass of liquid rather than solid for the heat evolved proved a challenge for some. Many candidates correctly combined their results, sometimes invoking Hess’ Law, in the final section, though many candidates benefited from the application of ECF.</p>
<div class="question_part_label">d.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>Most students scored well on naming the required compound from its formula in Part (a), likewise defining structural isomers and recognising compounds related in the way, required in Part (b), were rarely a challenge. In Part (c) students could usually identify whether compounds underwent oxidation and the products formed, with the most common mistake being to fail to notice that there was excess dichromate(VI) in the case of the primary alcohol. The mechanism required in Part (d) seemed to be known to many, though many candidates continue to lose marks through a lack of precision about the start and finish points of curly arrows. Many students gained at least one mark for the definition standard enthalpy change in the first section of Part (e), though few displayed the precision required for both marks. In the second section quite a few tried to solve the enthalpy problem by calorimetry rather than using the enthalpy of reaction that had been given. Generally speaking the next section, that did require calorimetry, was better done though the calculation of the amount of reagent and using the mass of liquid rather than solid for the heat evolved proved a challenge for some. Many candidates correctly combined their results, sometimes invoking Hess’ Law, in the final section, though many candidates benefited from the application of ECF.</p>
<div class="question_part_label">e.</div>
</div>
<br><hr><br><div class="specification">
<p>\({\text{25.0 c}}{{\text{m}}^{\text{3}}}\) of \({\text{0.200 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}\) ethanoic acid were added to \({\text{30.0 c}}{{\text{m}}^{\text{3}}}\) of a \({\text{0.150 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}\) sodium hydrogencarbonate solution, \({\text{NaHC}}{{\text{O}}_{\text{3}}}{\text{(aq)}}\).</p>
</div>
<div class="specification">
<p>The molar mass of a volatile organic liquid, <strong>X</strong>, can be determined experimentally by allowing it to vaporize completely at a controlled temperature and pressure. 0.348 g of <strong>X</strong> was injected into a gas syringe maintained at a temperature of 90 °C and a pressure of \(1.01 \times {10^5}{\text{ Pa}}\). Once it had reached equilibrium, the gas volume was measured as \({\text{95.0 c}}{{\text{m}}^{\text{3}}}\).</p>
</div>
<div class="specification">
<p>Bromoethane, \({\text{C}}{{\text{H}}_{\text{3}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{Br}}\), undergoes a substitution reaction to form ethanol, \({\text{C}}{{\text{H}}_{\text{3}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{OH}}\).</p>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Outline how electrical conductivity can be used to distinguish between a \({\text{0.200 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}\) solution of ethanoic acid, \({\text{C}}{{\text{H}}_{\text{3}}}{\text{COOH}}\), and a \({\text{0.200 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}\) solution of hydrochloric acid, HCl.</p>
<div class="marks">[1]</div>
<div class="question_part_label">a.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>(i) State an equation for the reaction of ethanoic acid with a solution of sodium hydrogencarbonate.</p>
<p> </p>
<p> </p>
<p>(ii) Determine which is the limiting reagent. Show your working.</p>
<p> </p>
<p> </p>
<p> </p>
<p> </p>
<p>(iii) Calculate the mass, in g, of carbon dioxide produced.</p>
<div class="marks">[5]</div>
<div class="question_part_label">b.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>(i) Determine the amount, in mol, of <strong>X </strong>in the gas syringe.</p>
<p> </p>
<p> </p>
<p> </p>
<p> </p>
<p> </p>
<p> </p>
<p>(ii) Calculate the molar mass of <strong>X</strong>.</p>
<div class="marks">[4]</div>
<div class="question_part_label">c.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>(i) Identify the reagent necessary for this reaction to occur.</p>
<p> </p>
<p>(ii) Deduce the mechanism for the reaction using equations and curly arrows to represent the movement of electron pairs.</p>
<div class="marks">[4]</div>
<div class="question_part_label">d.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Determine the enthalpy change, in kJ mol\(^{ - 1}\), for this reaction, using Table 10 of the Data Booklet.</p>
<div class="marks">[3]</div>
<div class="question_part_label">e.ii.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Bromoethene, \({\text{C}}{{\text{H}}_{\text{2}}}{\text{CHBr}}\), can undergo polymerization. Draw a section of this polymer that contains six carbon atoms.</p>
<div class="marks">[1]</div>
<div class="question_part_label">f.</div>
</div>
<h2 style="margin-top: 1em">Markscheme</h2>
<div class="question" style="padding-left: 20px;">
<p>HCl is a strong acid <strong>and </strong>\({\text{C}}{{\text{H}}_3}{\text{COOH}}\) is a weak acid so HCl has higher conductivity / HCl dissociates completely in water <strong>and </strong>\({\text{C}}{{\text{H}}_3}{\text{COOH}}\) does not, so HCl has higher conductivity / HCl is stronger acid (than \({\text{C}}{{\text{H}}_{\text{3}}}{\text{COOH}}\)) so has higher \({\text{[}}{{\text{H}}^ + }{\text{]}}\) and higher conductivity;</p>
<div class="question_part_label">a.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>(i) \({\text{C}}{{\text{H}}_3}{\text{COOH(aq)}} + {\text{HCO}}_3^ - {\text{(aq)}} \to {\text{C}}{{\text{H}}_3}{\text{CO}}{{\text{O}}^ - }{\text{(aq)}} + {{\text{H}}_2}{\text{O(l)}} + {\text{C}}{{\text{O}}_2}{\text{(g)}}\);</p>
<p><em>Accept NaHCO</em><sub><em>3</em></sub><em>(aq) and CH</em><sub><em>3</em></sub><em>COONa (aq) instead of ions.</em></p>
<p><em>Ignore state symbols.</em></p>
<p>(ii) \(n{\text{(C}}{{\text{H}}_3}{\text{COOH)}} = 0.00500{\text{ (mol)}}\) <strong>and</strong> \(n{\text{(NaHC}}{{\text{O}}_3}{\text{)}} = 0.00450{\text{ (mol)}}\);</p>
<p>\({\text{NaHC}}{{\text{O}}_3}\) is limiting;</p>
<p>(iii) \(n{\text{(C}}{{\text{O}}_2}{\text{)}} = n{\text{(NaHC}}{{\text{O}}_3}{\text{)}} = 0.00450{\text{ (mol)}}\);</p>
<p>\(m{\text{(C}}{{\text{O}}_2}{\text{)}} = 0.00450 \times 44.01 = 0.198{\text{ (g)}}\);</p>
<p><em>Award </em><strong><em>[2] </em></strong><em>for correct final answer.</em></p>
<div class="question_part_label">b.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>(i) \(T = 363{\text{ K}}\) <strong>and</strong> \(V = 9.50 \times {10^{ - 5}}{\text{ }}{{\text{m}}^3}\);</p>
<p><em>Accept V = 9.5 </em>\( \times \)<em> 10<sup>–2</sup></em><em> dm<sup>3</sup> </em><em>if P is used as 101 kPa in calculation.</em></p>
<p>\(n = \frac{{PV}}{{RT}} = \frac{{1.01 \times {{10}^5} \times 9.50 \times {{10}^{ - 5}}}}{{8.31 \times 363}}\);</p>
<p>\( = 3.18 \times {10^{ - 3}}{\text{ (mol)}}\);</p>
<p><em>Award </em><strong><em>[3] </em></strong><em>for correct final answer.</em></p>
<p>(ii) \(M = \left( {\frac{m}{n} = \frac{{0.348}}{{3.18 \times {{10}^{ - 3}}}} = } \right)109{\text{ }}({\text{g}}\,{\text{mo}}{{\text{l}}^{ - 1}})\);</p>
<div class="question_part_label">c.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>(i) (dilute aqueous) NaOH/sodium hydroxide / KOH/potassium hydroxide;</p>
<p><em>Do not accept hydroxide/OH</em><sup>–</sup><em>.</em></p>
<p>(ii) <img src="images/Schermafbeelding_2016-08-17_om_07.16.05.png" alt="M14/4/CHEMI/SP2/ENG/TZ1/07.d.ii/M"></p>
<p>curly arrow going from lone pair/negative charge on O in HO– to C;</p>
<p><em>Do not allow curly arrow originating on H in HO</em><sup>–</sup><em>.</em></p>
<p>curly arrow showing Br leaving;</p>
<p><em>Accept curly arrow either going from bond between C and Br to Br in bromoethane or in the transition state.</em></p>
<p>representation of transition state showing negative charge, square brackets and partial bonds;</p>
<p><em>Do not penalize if HO and Br are not at </em><em>180°</em> <em>to each other.</em></p>
<p><em>Do not award M3 if OH—C bond is represented.</em></p>
<div class="question_part_label">d.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p><em>bonds broken:</em></p>
<p>1(C=C) \( + 1\) (H–Br) / \((612 + 366 = )978{\text{ (kJ)}}\);</p>
<p><em>Accept 2630 (kJ).</em></p>
<p><em>bonds formed:</em></p>
<p>1(C–C) \( + 1\) (C–H) \( + 1\) (C–Br) / \((1 \times 347 + 1 \times 413 + 1 \times 290 = )1050{\text{ (kJ)}}\);</p>
<p><em>Accept 2702 (kJ).</em></p>
<p>\(\Delta H = - 72{\text{ }}({\text{kJ}}\,{\text{mo}}{{\text{l}}^{ - 1}})\);</p>
<p><em>Award </em><strong><em>[3] </em></strong><em>for correct final answer.</em></p>
<p><em>Award </em><strong><em>[2 max] </em></strong><em>for +72 (kJ mol</em><sup><em>−1</em></sup><em>).</em></p>
<div class="question_part_label">e.ii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p><img src="images/Schermafbeelding_2016-08-17_om_07.28.23.png" alt="M14/4/CHEMI/SP2/ENG/TZ1/07.f/M"> ;</p>
<p><em>Extension bonds required.</em></p>
<p><em>Ignore brackets and n.</em></p>
<div class="question_part_label">f.</div>
</div>
<h2 style="margin-top: 1em">Examiners report</h2>
<div class="question" style="padding-left: 20px;">
<p>Question 7 was answered by relatively few candidates, and those who chose this question were usually not well-prepared. In (a) very few candidates indicated that HCl is a strong acid and \({\text{C}}{{\text{H}}_{\text{3}}}{\text{COOH}}\) a weak one. Many candidates seemed unfamiliar with the distinction between state and outline and simply said that HCl would be a better conductor. In (b)(i) very few candidates could state a correct equation for the reaction between ethanoic acid and sodium hydrogencarbonate, even when the formulas were provided, but most could calculate the limiting reagent in (b)(ii) and the mass of \({\text{C}}{{\text{O}}_{\text{2}}}\) produced in (b)(iii). Part (c) gave details of a volatile organic liquid. Most candidates could calculate the moles of gas present in (c)(i), although the conversion to the correct units for pressure and volume gave many problems. The calculation of the molar mass of the gas, especially with ECF applied, was generally done well by the candidates. Part (d) referred to the substitution reaction of bromoethane to form ethanol. Identifying the reagent in (d)(i) for this reaction caused problems, with many stating \({\text{O}}{{\text{H}}^ - }\) as the reagent instead of NaOH or KOH. Only the best candidates could draw the mechanism for this substitution reaction in (d)(ii). Many candidates seemed to have very little idea of how to represent an \({{\text{S}}_{\text{N}}}{\text{2}}\) mechanism. Although most candidates identified HBr as the reagent which could produce bromoethane from ethene, they often gave UV as the required condition in (e)(i). Teachers should note that assessment statement 10.6.1 indicates that reagents, conditions and equations should be included for all reaction types listed in the syllabus. Calculation of the enthalpy change using bond enthalpies did not give problems to the good candidates in (e)(ii) but many of the weaker candidates failed to identify all the bonds broken and formed, and only scored the final mark through the application of ECF. Drawing a section of a polymer produced from bromoethene in (e)(iii) presented few problems for most candidates.</p>
<div class="question_part_label">a.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>Question 7 was answered by relatively few candidates, and those who chose this question were usually not well-prepared. In (a) very few candidates indicated that HCl is a strong acid and \({\text{C}}{{\text{H}}_{\text{3}}}{\text{COOH}}\) a weak one. Many candidates seemed unfamiliar with the distinction between state and outline and simply said that HCl would be a better conductor. In (b)(i) very few candidates could state a correct equation for the reaction between ethanoic acid and sodium hydrogencarbonate, even when the formulas were provided, but most could calculate the limiting reagent in (b)(ii) and the mass of \({\text{C}}{{\text{O}}_{\text{2}}}\) produced in (b)(iii). Part (c) gave details of a volatile organic liquid. Most candidates could calculate the moles of gas present in (c)(i), although the conversion to the correct units for pressure and volume gave many problems. The calculation of the molar mass of the gas, especially with ECF applied, was generally done well by the candidates. Part (d) referred to the substitution reaction of bromoethane to form ethanol. Identifying the reagent in (d)(i) for this reaction caused problems, with many stating \({\text{O}}{{\text{H}}^ - }\) as the reagent instead of NaOH or KOH. Only the best candidates could draw the mechanism for this substitution reaction in (d)(ii). Many candidates seemed to have very little idea of how to represent an \({{\text{S}}_{\text{N}}}{\text{2}}\) mechanism. Although most candidates identified HBr as the reagent which could produce bromoethane from ethene, they often gave UV as the required condition in (e)(i). Teachers should note that assessment statement 10.6.1 indicates that reagents, conditions and equations should be included for all reaction types listed in the syllabus. Calculation of the enthalpy change using bond enthalpies did not give problems to the good candidates in (e)(ii) but many of the weaker candidates failed to identify all the bonds broken and formed, and only scored the final mark through the application of ECF. Drawing a section of a polymer produced from bromoethene in (e)(iii) presented few problems for most candidates.</p>
<div class="question_part_label">b.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>Question 7 was answered by relatively few candidates, and those who chose this question were usually not well-prepared. In (a) very few candidates indicated that HCl is a strong acid and \({\text{C}}{{\text{H}}_{\text{3}}}{\text{COOH}}\) a weak one. Many candidates seemed unfamiliar with the distinction between state and outline and simply said that HCl would be a better conductor. In (b)(i) very few candidates could state a correct equation for the reaction between ethanoic acid and sodium hydrogencarbonate, even when the formulas were provided, but most could calculate the limiting reagent in (b)(ii) and the mass of \({\text{C}}{{\text{O}}_{\text{2}}}\) produced in (b)(iii). Part (c) gave details of a volatile organic liquid. Most candidates could calculate the moles of gas present in (c)(i), although the conversion to the correct units for pressure and volume gave many problems. The calculation of the molar mass of the gas, especially with ECF applied, was generally done well by the candidates. Part (d) referred to the substitution reaction of bromoethane to form ethanol. Identifying the reagent in (d)(i) for this reaction caused problems, with many stating \({\text{O}}{{\text{H}}^ - }\) as the reagent instead of NaOH or KOH. Only the best candidates could draw the mechanism for this substitution reaction in (d)(ii). Many candidates seemed to have very little idea of how to represent an \({{\text{S}}_{\text{N}}}{\text{2}}\) mechanism. Although most candidates identified HBr as the reagent which could produce bromoethane from ethene, they often gave UV as the required condition in (e)(i). Teachers should note that assessment statement 10.6.1 indicates that reagents, conditions and equations should be included for all reaction types listed in the syllabus. Calculation of the enthalpy change using bond enthalpies did not give problems to the good candidates in (e)(ii) but many of the weaker candidates failed to identify all the bonds broken and formed, and only scored the final mark through the application of ECF. Drawing a section of a polymer produced from bromoethene in (e)(iii) presented few problems for most candidates.</p>
<div class="question_part_label">c.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>Question 7 was answered by relatively few candidates, and those who chose this question were usually not well-prepared. In (a) very few candidates indicated that HCl is a strong acid and \({\text{C}}{{\text{H}}_{\text{3}}}{\text{COOH}}\) a weak one. Many candidates seemed unfamiliar with the distinction between state and outline and simply said that HCl would be a better conductor. In (b)(i) very few candidates could state a correct equation for the reaction between ethanoic acid and sodium hydrogencarbonate, even when the formulas were provided, but most could calculate the limiting reagent in (b)(ii) and the mass of \({\text{C}}{{\text{O}}_{\text{2}}}\) produced in (b)(iii). Part (c) gave details of a volatile organic liquid. Most candidates could calculate the moles of gas present in (c)(i), although the conversion to the correct units for pressure and volume gave many problems. The calculation of the molar mass of the gas, especially with ECF applied, was generally done well by the candidates. Part (d) referred to the substitution reaction of bromoethane to form ethanol. Identifying the reagent in (d)(i) for this reaction caused problems, with many stating \({\text{O}}{{\text{H}}^ - }\) as the reagent instead of NaOH or KOH. Only the best candidates could draw the mechanism for this substitution reaction in (d)(ii). Many candidates seemed to have very little idea of how to represent an \({{\text{S}}_{\text{N}}}{\text{2}}\) mechanism. Although most candidates identified HBr as the reagent which could produce bromoethane from ethene, they often gave UV as the required condition in (e)(i). Teachers should note that assessment statement 10.6.1 indicates that reagents, conditions and equations should be included for all reaction types listed in the syllabus. Calculation of the enthalpy change using bond enthalpies did not give problems to the good candidates in (e)(ii) but many of the weaker candidates failed to identify all the bonds broken and formed, and only scored the final mark through the application of ECF. Drawing a section of a polymer produced from bromoethene in (e)(iii) presented few problems for most candidates.</p>
<div class="question_part_label">d.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>Question 7 was answered by relatively few candidates, and those who chose this question were usually not well-prepared. In (a) very few candidates indicated that HCl is a strong acid and \({\text{C}}{{\text{H}}_{\text{3}}}{\text{COOH}}\) a weak one. Many candidates seemed unfamiliar with the distinction between state and outline and simply said that HCl would be a better conductor. In (b)(i) very few candidates could state a correct equation for the reaction between ethanoic acid and sodium hydrogencarbonate, even when the formulas were provided, but most could calculate the limiting reagent in (b)(ii) and the mass of \({\text{C}}{{\text{O}}_{\text{2}}}\) produced in (b)(iii). Part (c) gave details of a volatile organic liquid. Most candidates could calculate the moles of gas present in (c)(i), although the conversion to the correct units for pressure and volume gave many problems. The calculation of the molar mass of the gas, especially with ECF applied, was generally done well by the candidates. Part (d) referred to the substitution reaction of bromoethane to form ethanol. Identifying the reagent in (d)(i) for this reaction caused problems, with many stating \({\text{O}}{{\text{H}}^ - }\) as the reagent instead of NaOH or KOH. Only the best candidates could draw the mechanism for this substitution reaction in (d)(ii). Many candidates seemed to have very little idea of how to represent an \({{\text{S}}_{\text{N}}}{\text{2}}\) mechanism. Although most candidates identified HBr as the reagent which could produce bromoethane from ethene, they often gave UV as the required condition in (e)(i). Teachers should note that assessment statement 10.6.1 indicates that reagents, conditions and equations should be included for all reaction types listed in the syllabus. Calculation of the enthalpy change using bond enthalpies did not give problems to the good candidates in (e)(ii) but many of the weaker candidates failed to identify all the bonds broken and formed, and only scored the final mark through the application of ECF. Drawing a section of a polymer produced from bromoethene in (e)(iii) presented few problems for most candidates.</p>
<div class="question_part_label">e.ii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>Question 7 was answered by relatively few candidates, and those who chose this question were usually not well-prepared. In (a) very few candidates indicated that HCl is a strong acid and \({\text{C}}{{\text{H}}_{\text{3}}}{\text{COOH}}\) a weak one. Many candidates seemed unfamiliar with the distinction between state and outline and simply said that HCl would be a better conductor. In (b)(i) very few candidates could state a correct equation for the reaction between ethanoic acid and sodium hydrogencarbonate, even when the formulas were provided, but most could calculate the limiting reagent in (b)(ii) and the mass of \({\text{C}}{{\text{O}}_{\text{2}}}\) produced in (b)(iii). Part (c) gave details of a volatile organic liquid. Most candidates could calculate the moles of gas present in (c)(i), although the conversion to the correct units for pressure and volume gave many problems. The calculation of the molar mass of the gas, especially with ECF applied, was generally done well by the candidates. Part (d) referred to the substitution reaction of bromoethane to form ethanol. Identifying the reagent in (d)(i) for this reaction caused problems, with many stating \({\text{O}}{{\text{H}}^ - }\) as the reagent instead of NaOH or KOH. Only the best candidates could draw the mechanism for this substitution reaction in (d)(ii). Many candidates seemed to have very little idea of how to represent an \({{\text{S}}_{\text{N}}}{\text{2}}\) mechanism. Although most candidates identified HBr as the reagent which could produce bromoethane from ethene, they often gave UV as the required condition in (e)(i). Teachers should note that assessment statement 10.6.1 indicates that reagents, conditions and equations should be included for all reaction types listed in the syllabus. Calculation of the enthalpy change using bond enthalpies did not give problems to the good candidates in (e)(ii) but many of the weaker candidates failed to identify all the bonds broken and formed, and only scored the final mark through the application of ECF. Drawing a section of a polymer produced from bromoethene in (e)(iii) presented few problems for most candidates.</p>
<div class="question_part_label">f.</div>
</div>
<br><hr><br><div class="specification">
<p class="p1">Ethene belongs to the homologous series of the alkenes.</p>
</div>
<div class="specification">
<p class="p1">A bromoalkane, \({{\text{C}}_{\text{4}}}{{\text{H}}_{\text{9}}}{\text{Br}}\), reacts with a warm, aqueous sodium hydroxide solution, NaOH.</p>
</div>
<div class="specification">
<p class="p1">The time taken to produce a certain amount of product using different initial concentrations of \({{\text{C}}_{\text{4}}}{{\text{H}}_{\text{9}}}{\text{Br}}\) and NaOH is measured. The results are shown in the following table.</p>
<p class="p1" style="text-align: center;"><img src="images/Schermafbeelding_2016-09-14_om_16.46.57.png" alt="M13/4/CHEMI/SP2/ENG/TZ1/08.c"></p>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">Outline <strong>three </strong>features of a homologous series.</p>
<div class="marks">[3]</div>
<div class="question_part_label">a.i.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">Describe a test to distinguish ethene from ethane, including what is observed in <strong>each </strong>case.</p>
<div class="marks">[2]</div>
<div class="question_part_label">a.ii.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">Bromoethane can be produced either from ethene or from ethane. State an equation for <strong>each </strong>reaction.</p>
<div class="marks">[2]</div>
<div class="question_part_label">a.iii.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">State the equation for the reaction of \({{\text{C}}_{\text{4}}}{{\text{H}}_{\text{9}}}{\text{Br}}\) with NaOH.</p>
<div class="marks">[1]</div>
<div class="question_part_label">b.i.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">Suggest what would happen to the pH of the solution as the reaction proceeds.</p>
<div class="marks">[1]</div>
<div class="question_part_label">b.ii.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">Deduce the effect of the concentration of \({{\text{C}}_{\text{4}}}{{\text{H}}_{\text{9}}}{\text{Br}}\) and NaOH on the rate of reaction.</p>
<p class="p2"> </p>
<p class="p1">C<sub><span class="s1">4</span></sub>H<sub><span class="s1">9</span></sub>Br:</p>
<p class="p2"> </p>
<p class="p2"> </p>
<p class="p1">NaOH:</p>
<div class="marks">[2]</div>
<div class="question_part_label">c.i.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">Suggest why <strong>warm </strong>sodium hydroxide solution is used.</p>
<div class="marks">[1]</div>
<div class="question_part_label">c.ii.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">Deduce whether C<sub><span class="s1">4</span></sub>H<sub><span class="s1">9</span></sub>Br is a primary or tertiary halogenoalkane.</p>
<div class="marks">[2]</div>
<div class="question_part_label">c.iii.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">Determine the structural formula of C<sub><span class="s1">4</span></sub>H<sub><span class="s1">9</span></sub>Br.</p>
<div class="marks">[1]</div>
<div class="question_part_label">c.iv.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">Describe, using an equation, how \({{\text{C}}_{\text{4}}}{{\text{H}}_{\text{9}}}{\text{Br}}\) can be converted into \({{\text{C}}_{\text{4}}}{{\text{H}}_{\text{8}}}{\text{B}}{{\text{r}}_{\text{2}}}\).</p>
<div class="marks">[1]</div>
<div class="question_part_label">c.v.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">Explain the mechanism for the reaction in (c) of \({{\text{C}}_{\text{4}}}{{\text{H}}_{\text{9}}}{\text{Br}}\) with NaOH, using curly arrows to represent the movement of electron pairs.</p>
<div class="marks">[4]</div>
<div class="question_part_label">d.</div>
</div>
<h2 style="margin-top: 1em">Markscheme</h2>
<div class="question" style="padding-left: 20px;">
<p class="p1">same functional group / same general formula;</p>
<p class="p1">difference between successive members is \({\text{C}}{{\text{H}}_{\text{2}}}\);</p>
<p class="p1">similar chemical properties;</p>
<p class="p1"><em>Do not accept “same” chemical properties.</em></p>
<p class="p1">gradually changing physical properties;</p>
<div class="question_part_label">a.i.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">adding bromine (water);</p>
<p class="p1"><em>ethene: </em>brown/orange to colourless / decolourizes bromine water <strong>and</strong></p>
<p class="p1"><em>ethane: </em>does not change colour;</p>
<p class="p1"><strong>OR</strong></p>
<p class="p1">adding <span class="s1">acidified</span> potassium permanganate solution/\({\text{KMn}}{{\text{O}}_{\text{4}}}{\text{(aq)}}\);</p>
<p class="p1"><em>ethene: </em>purple to colourless/brown <strong>and</strong></p>
<p class="p1"><em>ethane: </em>does not change colour;</p>
<p class="p1"><strong>OR</strong></p>
<p class="p1">adding Baeyer’s reagent;</p>
<p class="p1"><em>ethene: </em>purple/pink to brown <strong>and</strong></p>
<p class="p1"><em>ethane: </em>does not change colour;</p>
<p class="p1"><em>Do not accept “clear” or “transparent” for “colourless”.</em></p>
<div class="question_part_label">a.ii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">\({{\text{C}}_{\text{2}}}{{\text{H}}_{\text{4}}} + {\text{HBr}} \to {{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}}{\text{Br}}\);</p>
<p class="p1">\({{\text{C}}_2}{{\text{H}}_6} + {\text{B}}{{\text{r}}_2} \to {{\text{C}}_2}{{\text{H}}_5}{\text{Br}} + {\text{HBr}}\);</p>
<p class="p1"><em>Accept structural formulas.</em></p>
<p class="p1"><em>Penalise missing H atoms or incorrect bonds (such as C–HO, C–H<sub>2</sub>C) in structural formulas only once in the paper.</em></p>
<div class="question_part_label">a.iii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">\({{\text{C}}_4}{{\text{H}}_9}{\text{Br}} + {\text{O}}{{\text{H}}^ - } \to {{\text{C}}_4}{{\text{H}}_9}{\text{OH}} + {\text{B}}{{\text{r}}^ - }\);</p>
<p class="p1"><em>Accept NaOH in the equation.</em></p>
<div class="question_part_label">b.i.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">decreases;</p>
<div class="question_part_label">b.ii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1"><em>C</em><sub><span class="s1"><em>4</em></span></sub><em>H</em><sub><span class="s1"><em>9</em></span></sub><em>Br:</em></p>
<p class="p1">[C<sub><em>4</em></sub>H<sub><span class="s1">9</span></sub>Br] doubles <strong>and </strong>time halves/rate doubles / rate proportional to [C<sub><span class="s1">4</span></sub>H<sub><span class="s1">9</span></sub>Br];</p>
<p class="p1"><em>Do not accept rate increases when [C</em><sub><span class="s1"><em>4</em></span></sub><em>H</em><sub><span class="s1"><em>9</em></span></sub><em>Br] increases.</em></p>
<p class="p1"><em>NaOH:</em></p>
<p class="p1">[NaOH] doubles <strong>and </strong>time/rate does not change / rate independent of [NaOH];</p>
<div class="question_part_label">c.i.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">increases rate;</p>
<p class="p1"><em>Accept increases number of collisions.</em></p>
<div class="question_part_label">c.ii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">rate depends on \({\text{[}}{{\text{C}}_{\text{4}}}{{\text{H}}_{\text{9}}}{\text{Br]}}\) <span style="text-decoration: underline;">only</span> / rate does not depend on \({\text{[O}}{{\text{H}}^ - }{\text{]}}\) / \({{\text{S}}_{\text{N}}}{\text{1}}\) reaction /</p>
<p class="p1">first order reaction / if it was primary, reaction would be \({{\text{S}}_{\text{N}}}{\text{2}}\);</p>
<p class="p1">tertiary;</p>
<p class="p1"><em>Accept ECF.</em></p>
<div class="question_part_label">c.iii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">\({{\text{(C}}{{\text{H}}_{\text{3}}}{\text{)}}_{\text{3}}}{\text{CBr}}\);</p>
<p class="p1"><em>Allow both condensed and full structural formula.</em></p>
<p class="p1"><em>Accept ECF.</em></p>
<div class="question_part_label">c.iv.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">\({{\text{C}}_{\text{4}}}{{\text{H}}_{\text{9}}}{\text{Br}} + {\text{B}}{{\text{r}}_{\text{2}}} \to {{\text{C}}_{\text{4}}}{{\text{H}}_{\text{8}}}{\text{B}}{{\text{r}}_{\text{2}}} + {\text{HBr}}\);</p>
<div class="question_part_label">c.v.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1"><img src="images/Schermafbeelding_2016-09-15_om_06.56.46.png" alt="M13/4/CHEMI/SP2/ENG/TZ1/08.d_1/M"></p>
<p class="p1">curly arrow showing \({\text{B}}{{\text{r}}^ - }\) leaving;</p>
<p class="p2">representation of tertiary carbocation;</p>
<p class="p2">curly arrow going from lone pair/negative charge on O in \(^ - {\text{OH}}\) to \({{\text{C}}^ + }\);</p>
<p class="p2"><em>Do not allow arrow originating on H in </em><sup><span class="s1">–</span></sup><em>OH</em>.</p>
<p class="p2">formation of \({{\text{(C}}{{\text{H}}_{\text{3}}}{\text{)}}_{\text{3}}}{\text{COH}}\) <strong>and </strong>\({\text{B}}{{\text{r}}^ - }\);</p>
<p class="p2"><em>Accept Br<sup>–</sup></em><span class="s1"><em> </em></span><em>anywhere on product side in the reaction scheme.</em></p>
<p class="p2"><em>If primary halogenoalkane has been answered in (c)(iii) apply ECF for the mechanism:</em></p>
<p class="p3"><img src="images/Schermafbeelding_2016-09-15_om_06.57.59.png" alt="M13/4/CHEMI/SP2/ENG/TZ1/08.d_2/M"></p>
<p class="p2">curly arrow going from lone pair/negative charge on O in \(^ - {\text{OH}}\) to C;</p>
<p class="p2"><em>Do not allow curly arrow originating on H in </em><sup><span class="s1"><em>–</em></span></sup><em>OH.</em></p>
<p class="p2">curly arrow showing \({\text{B}}{{\text{r}}^ - }\) leaving;</p>
<p class="p2"><em>Accept curly arrow either going from bond between C and Br to Br in bromobutane or in the transition state.</em></p>
<p class="p2">representation of transition state showing negative charge, square brackets and partial bond;</p>
<p class="p2"><em>Do not penalize if HO and Br are not at 180°</em> <em>to each other.</em></p>
<p class="p2"><em>Do not award M3 if OH—C bond is represented.</em></p>
<p class="p2">formation of organic product \({{\text{C}}_{\text{4}}}{{\text{H}}_{\text{9}}}{\text{OH}}\) <strong>and </strong>\({\text{B}}{{\text{r}}^ - }\);</p>
<p class="p2"><em>Accept Br</em><span class="s1"><em>– </em></span><em>anywhere on product side in the reaction scheme.</em></p>
<div class="question_part_label">d.</div>
</div>
<h2 style="margin-top: 1em">Examiners report</h2>
<div class="question" style="padding-left: 20px;">
<p class="p1">Students had surprisingly difficulties to name the features of a homologous series. Common mistakes were to say SAME chemical or physical properties or same empirical/molecular/structural formula.</p>
<div class="question_part_label">a.i.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">Most candidates did well describing the test to distinguish alkanes and alkenes.</p>
<div class="question_part_label">a.ii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">The formation of dibromobutane was a common error.</p>
<div class="question_part_label">a.iii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">The equation for the reaction of the \({{\text{C}}_{\text{4}}}{{\text{H}}_{\text{9}}}{\text{Br}}\) with NaOH presented no problem.</p>
<div class="question_part_label">b.i.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">Some did not realize that pH decreases as NaOH is reacting, often referring as the pH would become more neutral.</p>
<div class="question_part_label">b.ii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">Candidates could deduce that the concentration of NaOH does not affect the rate, but could not accurately explain and quantify the relationship between the concentration of C<sub><span class="s1">4</span></sub>H<sub><span class="s1">9</span></sub>Br and the rate of reaction. Time and rate were often confused.</p>
<div class="question_part_label">c.i.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">This was well answered.</p>
<div class="question_part_label">c.ii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">Very few candidates could relate rate information to deduce that \({{\text{C}}_{\text{4}}}{{\text{H}}_{\text{9}}}{\text{Br}}\) was tertiary.</p>
<div class="question_part_label">c.iii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">The structural formula was generally gained by ECF.</p>
<div class="question_part_label">c.iv.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">Students did not have problems with the equation.</p>
<div class="question_part_label">c.v.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">Mechanism with curly arrows was done very poorly, students confused \({{\text{S}}_{\text{N}}}{\text{1}}\) and \({{\text{S}}_{\text{N}}}{\text{2}}\) mechanisms, drew arrows that did not show clearly origin and end or did not draw any arrow at all.</p>
<div class="question_part_label">d.</div>
</div>
<br><hr><br><div class="specification">
<p class="p1">In an experiment to measure the enthalpy change of combustion of ethanol, a student heated a copper calorimeter containing 100 cm<sup><span class="s1">3 </span></sup>of water with a spirit lamp and collected the following data.</p>
<p class="p1">\[\begin{array}{*{20}{l}} {{\text{Initial temperature of water:}}}&{{\text{20.0 }}^\circ {\text{C}}} \\ {{\text{Final temperature of water:}}}&{{\text{55.0 }}^\circ {\text{C}}} \\ {{\text{Mass of ethanol burned:}}}&{{\text{1.78 g}}} \\ {{\text{Density of water:}}}&{{\text{1.00 g}}\,{\text{c}}{{\text{m}}^{ - 3}}} \end{array}\]</p>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">(i) Use the data to calculate the heat evolved when the ethanol was combusted.</p>
<p class="p1">(ii) Calculate the enthalpy change of combustion per mole of ethanol.</p>
<p class="p1">(iii) Suggest two reasons why the result is not the same as the value in the Data Booklet.</p>
<div class="marks">[6]</div>
<div class="question_part_label">a.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">Ethanol is part of the homologous series of alcohols. Describe <strong>two </strong>features of a homologous series.</p>
<div class="marks">[2]</div>
<div class="question_part_label">b.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">(i) Below are <strong>four structural </strong>isomers of alcohols with molecular formula \({{\text{C}}_{\text{4}}}{{\text{H}}_{{\text{10}}}}{\text{O}}\). State the name of each of the isomers <strong>a</strong>, <strong>b</strong>, <strong>c </strong>and <strong>D</strong>.</p>
<p class="p1" style="text-align: center;"><img src="images/Schermafbeelding_2016-10-07_om_09.52.00.png" alt="M10/4/CHEMI/SP2/ENG/TZ1/06.d"></p>
<p class="p1">(ii) <span class="Apple-converted-space"> </span>Determine the isomer that cannot be oxidized by acidifi ed potassium dichromate(VI), \({{\text{K}}_{\text{2}}}{\text{C}}{{\text{r}}_{\text{2}}}{{\text{O}}_{\text{7}}}\).</p>
<p class="p1">(iii) <span class="Apple-converted-space"> </span>Determine the isomer which can be oxidized to butanal.</p>
<p class="p1">(iv) <span class="Apple-converted-space"> </span>Determine the isomer which can be oxidized to butanone.</p>
<p class="p1">(v) <span class="Apple-converted-space"> </span>Suggest the structural formula of another isomer of \({{\text{C}}_{\text{4}}}{{\text{H}}_{{\text{10}}}}{\text{O}}\).</p>
<div class="marks">[8]</div>
<div class="question_part_label">c.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1" style="text-align: center;"><img src="images/Schermafbeelding_2016-10-07_om_09.52.00.png" alt="M10/4/CHEMI/SP2/ENG/TZ1/06.d"></p>
<p class="p1">(i) Isomer <strong>a </strong>is formed by reacting 1-bromobutane with aqueous sodium hydroxide. State whether the reaction would proceed via an S<sub><span class="s1">N</span></sub>1 or S<sub><span class="s1">N</span></sub>2 mechanism.</p>
<p class="p1">(ii) Explain the mechanism named in part (d) (i) using curly arrows to represent the movement of electron pairs.</p>
<div class="marks">[4]</div>
<div class="question_part_label">d.</div>
</div>
<h2 style="margin-top: 1em">Markscheme</h2>
<div class="question" style="padding-left: 20px;">
<p class="p1">(i) <span class="Apple-converted-space"> </span>\(100 \times 4.18 \times 35.0\);</p>
<p class="p1">14630 J / 14600 J / 14.6 kJ;</p>
<p class="p1"><em>Award </em><strong><em>[2] </em></strong><em>for correct final answer.</em></p>
<p class="p1"><em>No ECF here if incorrect mass used.</em></p>
<p class="p1">(ii) <span class="Apple-converted-space"> </span>\(\frac{{1.78}}{{46.08}} = 0.0386{\text{ mol}}\);</p>
<p class="p1">\(\frac{{14.6}}{{0.0386}} = ( - )378{\text{ kJ}}\,{\text{mo}}{{\text{l}}^{ - 1}}\);</p>
<p class="p1"><em>Accept (–)377 and (–)379 kJ</em>\(\,\)<em>mol</em><sup><span class="s1"><em>–1</em></span></sup><em>.</em></p>
<p class="p1"><em>Award </em><strong><em>[2] </em></strong><em>for correct final answer.</em></p>
<p class="p1">(iii) <span class="Apple-converted-space"> </span>heat loss;</p>
<p class="p1">incomplete combustion;</p>
<p class="p1">heat absorbed by calorimeter not included;</p>
<p class="p1"><em>Accept other sensible suggestions.</em></p>
<div class="question_part_label">a.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">same general formula;</p>
<p class="p1">same functional group;</p>
<p class="p1">successive members differ by CH<sub><span class="s1">2</span></sub>;</p>
<p class="p1"><em>Allow methylene for CH</em><sub><span class="s1"><em>2</em></span></sub><em>.</em></p>
<p class="p1">similar chemical properties;</p>
<p class="p1">gradually changing physical properties;</p>
<div class="question_part_label">b.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">(i) <span class="Apple-converted-space"> </span><strong>A</strong>: butan-1-ol;</p>
<p class="p1"><strong>B</strong>: butan-2-ol;</p>
<p class="p1"><strong>C</strong>: (2-)methylpropan-2-ol;</p>
<p class="p1"><strong>D</strong>: (2-)methylpropan-1-ol;</p>
<p class="p1"><em>Accept answers in the form of 1-butanol and 2-methyl-2-propanol etc.</em></p>
<p class="p1"><em>Penalize incorrect punctuation, e.g. commas for hyphens, only once.</em></p>
<p class="p1">(ii) <span class="Apple-converted-space"> </span><strong>C/</strong>(2-)methylpropan-2-ol;</p>
<p class="p1">(iii) <span class="Apple-converted-space"> </span><strong>A</strong>/butan-1-ol;</p>
<p class="p1">(iv) <span class="Apple-converted-space"> </span><strong>B</strong>/butan-2-ol;</p>
<p class="p1">(v)<span class="Apple-converted-space"> </span><img src="images/Schermafbeelding_2016-10-07_om_13.46.55.png" alt="M10/4/CHEMI/SP2/ENG/TZ1/06.c/M"></p>
<div class="question_part_label">c.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">(i) S<sub><span class="s1">N</span></sub>2;</p>
<p class="p1">(ii) <img src="images/Schermafbeelding_2016-10-07_om_13.54.18.png" alt="M10/4/CHEMI/SP2/ENG/TZ1/06.d/M"></p>
<p class="p1">curly arrow going from lone pair/negative charge on O in \({\text{O}}{{\text{H}}^ - }\) to C;</p>
<p class="p1"><em>Do not allow curly arrow originating on H in OH</em><sup><span class="s1"><em>–</em></span></sup><em>.</em></p>
<p class="p1">curly arrow showing Br leaving;</p>
<p class="p1"><em>Accept curly arrow either going from bond between C and Br to Br in 1-</em><em>bromobutane or in the transition state.</em></p>
<p class="p1">representation of transition state showing negative charge, square brackets and partial bonds;</p>
<p class="p1"><em>Do not penalize if HO and Br are not at 180°</em><span class="s1"><em> </em></span><em>to each other.</em></p>
<p class="p1"><em>Do not award M3 if OH----C bond is represented.</em></p>
<div class="question_part_label">d.</div>
</div>
<h2 style="margin-top: 1em">Examiners report</h2>
<div class="question" style="padding-left: 20px;">
<p class="p1">This was the least popular of the Section B questions. (a) (i) was poorly answered. Many candidates had no idea and some candidates used the mass of ethanol instead of water. A few calculated correctly but failed to convert the mass of water to kg, or kJ to J, thereby ending up with the wrong unit for the answer. Only a small minority of candidates got (ii) correct. (iii) was well answered. Nearly all candidates referred to heat loss but only the better candidates were able to give a second reason.</p>
<div class="question_part_label">a.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">Most candidates were able to describe two features of a homologous series in (b).</p>
<div class="question_part_label">b.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">(c) was usually well done, but some candidates struggled with the structural formula of the ether isomer of \({{\text{C}}_{\text{4}}}{{\text{H}}_{{\text{10}}}}{\text{O}}\) in (v).</p>
<p class="p1">One G2 comment stated that the ether functional group is not listed as one of the formal functional groups in Topic 10, which is correct. However, this aspect has been asked previously on SL papers in relation to deducing specific isomers (rather than naming the ether group) and although candidates are not required to know that C-O-C is the ether functional group, there is an expectation that they should be able to deduce an isomer based on C-O-C, as this is cited explicitly in AS 4.3.2, in the teacher’s notes in relation to \({\text{C}}{{\text{H}}_{\text{3}}}{\text{OC}}{{\text{H}}_{\text{3}}}\) and \({\text{C}}{{\text{H}}_{\text{3}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{OH}}\), making this very much an objective 3 question, linking concepts across the syllabus.</p>
<div class="question_part_label">c.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">S<sub>N</sub>2 was commonly given but the mechanism in (ii) was exceptionally poorly answered in this session. In particular, the transition state was rarely drawn, and clearly candidates were not prepared for organic reaction mechanisms, even though there are only a few such examples on the syllabus as a whole.</p>
<div class="question_part_label">d.</div>
</div>
<br><hr><br><div class="specification">
<p class="p1">Alkenes, alcohols and esters are three families of organic compounds with many commercial uses.</p>
</div>
<div class="specification">
<p class="p1">Esters are often used in perfumes. Analysis of a compound containing the ester functional group only, gives a percentage composition by mass of C: 62.0% and H: 10.4%.</p>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">State the meaning of the term <em>structural isomers</em>.</p>
<div class="marks">[1]</div>
<div class="question_part_label">a.ii.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1"><strong>X </strong>is an isomer of C<sub><span class="s1">4</span></sub>H<sub><span class="s1">8 </span></sub>and has the structural formula shown below.</p>
<p class="p1" style="text-align: center;"><img src="images/Schermafbeelding_2016-09-23_om_13.10.03.png" alt="N12/4/CHEMI/SP2/ENG/TZ0/06.a.iii"></p>
<p class="p1">Apply IUPAC rules to name this isomer. Deduce the structural formulas of <strong>two</strong> other isomers of C<sub><span class="s1">4</span></sub>H<sub><span class="s1">8</span></sub>.</p>
<div class="marks">[3]</div>
<div class="question_part_label">a.iii.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">State the balanced chemical equation for the reaction of <strong>X </strong>with HBr to form <strong>Y</strong>.</p>
<div class="marks">[1]</div>
<div class="question_part_label">a.iv.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1"><strong>Y </strong>reacts with aqueous sodium hydroxide, NaOH(aq), to form an alcohol, <strong>Z</strong>. Identify whether <strong>Z </strong>is a primary, secondary or tertiary alcohol.</p>
<div class="marks">[1]</div>
<div class="question_part_label">a.v.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">Explain <strong>one </strong>suitable mechanism for the reaction in (v) using curly arrows to represent the movement of electron pairs.</p>
<div class="marks">[4]</div>
<div class="question_part_label">a.vi.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">Deduce the structural formula of the organic product formed when <strong>Z </strong>is oxidized by heating under reflux with acidified potassium dichromate(VI) <strong>and </strong>state the name of the functional group of this organic product.</p>
<div class="marks">[2]</div>
<div class="question_part_label">a.vii.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">Draw the ester functional group.</p>
<div class="marks">[1]</div>
<div class="question_part_label">b.i.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">Determine the empirical formula of the ester, showing your working.</p>
<div class="marks">[4]</div>
<div class="question_part_label">b.ii.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">The molar mass of the ester is \({\text{116.18 g}}\,{\text{mo}}{{\text{l}}^{ - 1}}\). Determine its molecular formula.</p>
<div class="marks">[1]</div>
<div class="question_part_label">b.iii.</div>
</div>
<h2 style="margin-top: 1em">Markscheme</h2>
<div class="question" style="padding-left: 20px;">
<p class="p1">compounds with the same molecular formula but different arrangement of atoms/structural formula/structures;</p>
<p class="p1"><em>Do not allow similar instead of same.</em></p>
<div class="question_part_label">a.ii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">(<em>cis</em>-)but-2-ene / (<em>Z</em>)but-2-ene / but-2-ene;</p>
<p class="p1"><em>Accept (cis-)2-butene / Z-2-butene.</em></p>
<p class="p1"><em>Ignore missing hyphens.</em></p>
<p class="p2">CH<sub>3</sub>CH<sub>2</sub>CH=CH<sub>2</sub><span class="s2">;</span></p>
<p class="p2">H<sub>2</sub>C=C(CH<sub>3</sub>)<sub>2</sub><span class="s2">;</span></p>
<p class="p2"><em>Accept either full or condensed structural formulas.</em></p>
<p class="p1"><em>Allow structural formula of trans-but-2-ene.</em></p>
<div class="question_part_label">a.iii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">(CH<sub>3</sub>)CH=CH(CH<sub>3</sub>) + HBr \( \to \) CH<sub>3</sub>CHBrCH<sub>2</sub>CH<sub>3</sub><span class="s1">;</span></p>
<p class="p1"><span class="s1"><em>Allow </em></span><em>C<sub>4</sub>H<sub>8</sub> </em><span class="s3">+ </span><em>HBr \( \to \) </em><em>C<sub>4</sub>H<sub>9</sub>Br</em><span class="s1"><em>.</em></span></p>
<div class="question_part_label">a.iv.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">secondary/ 2°;</p>
<div class="question_part_label">a.v.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1"><em>Since secondary could be either S</em><sub><span class="s1"><em>N</em></span></sub><em>1 or S</em><sub><span class="s1"><em>N</em></span></sub><em>2 so allow S</em><sub><span class="s1"><em>N</em></span></sub><em>1 or S</em><sub><span class="s1"><em>N</em></span></sub><em>2 for M1–M4.</em></p>
<p class="p1"><em>S</em><span class="s1"><em><sub>N</sub>1:</em></span></p>
<p class="p1"> </p>
<p class="p1"><img src="images/Schermafbeelding_2016-09-23_om_13.26.05.png" alt="N12/4/CHEMI/SP2/ENG/TZ0/06.a.vi_1/M"></p>
<p class="p1">curly arrow showing Br leaving;</p>
<p class="p1"><em>Do not allow arrow originating from C to C–Br bond.</em></p>
<p class="p1">representation of secondary carbocation;</p>
<p class="p1">curly arrow going from lone pair/negative charge on O in HO<sup><span class="s1">– </span></sup>to C<sup><span class="s1">+</span></sup>;</p>
<p class="p1"><em>Do not allow arrow originating on H in HO</em><sup><span class="s1"><em>–</em></span></sup><em>.</em></p>
<p class="p1">formation of organic product CH<sub><span class="s1">3</span></sub>CH(OH)C<sub><span class="s1">2</span></sub>H<sub><span class="s1">5</span></sub>/C<sub><span class="s1">4</span></sub>H<sub><span class="s1">9</span></sub>OH <strong>and </strong>Br<sup><span class="s1">–</span></sup>;</p>
<p class="p1"><em>Allow formation of NaBr instead of Br</em><sup><span class="s1">–</span></sup>.</p>
<p class="p1"><strong>OR</strong></p>
<p class="p1"><em>S</em><sub><span class="s1"><em>N</em></span></sub><em>2:</em></p>
<p class="p1"><img src="images/Schermafbeelding_2016-09-23_om_13.29.30.png" alt="N12/4/CHEMI/SP2/ENG/TZ0/06.a.vi_2/M"></p>
<p class="p1">curly arrow going from lone pair/negative charge on O in HO– to C;</p>
<p class="p1"><em>Do not allow curly arrow originating on H in HO</em><sup><span class="s1"><em>–</em></span></sup><em>.</em></p>
<p class="p1">curly arrow showing Br leaving;</p>
<p class="p1"><em>Accept curly arrow either going from bond between C and Br to Br in </em><em>2-bromobutane or in the transition state.</em></p>
<p class="p1"><em>Do not allow arrow originating from C to C–Br bond.</em></p>
<p class="p1">representation of transition state showing negative charge, square brackets and partial bonds;</p>
<p class="p1"><em>Do not penalize if HO and Br are not at 180° </em><em>to each other.</em></p>
<p class="p1"><em>Do not award M3 if OH ---- C bond is represented.</em></p>
<p class="p1">formation of organic product CH<sub><span class="s1">3</span></sub>CH(OH)C<sub><span class="s1">2</span></sub>H<sub><span class="s1">5</span></sub>/C<sub><span class="s1">4</span></sub>H<sub><span class="s1">9</span></sub>OH <strong>and </strong>Br<sup><span class="s1">–</span></sup>;</p>
<p class="p1"><em>Allow formation of NaBr instead of Br</em><sup><span class="s1">–</span></sup>.</p>
<p class="p1"><em>For primary </em><strong><em>Z </em></strong><em>from (v), for ECF S</em><sub><span class="s1"><em>N</em></span></sub><em>2 required.</em></p>
<p class="p1"><em>For tertiary </em><strong><em>Z </em></strong><em>from (v), for ECF S</em><sub><span class="s1"><em>N</em></span></sub><em>1 required.</em></p>
<p class="p1"><em>But curly arrow showing Br leaving and formation of C</em><sub><span class="s1"><em>4</em></span></sub><em>H</em><sub><span class="s1"><em>9</em></span></sub><em>OH </em><strong><em>and </em></strong><em>Br</em><sup><span class="s1"><em>– </em></span></sup><em>can </em><em>be scored for either mechanism (even if incorrect type).</em></p>
<p class="p1"><em>For primary </em><strong><em>Z </em></strong><em>from (v) with 1-bromobutane stated in (vi), correct S</em><sub><span class="s1"><em>N</em></span></sub><em>2 can </em><em>score full marks.</em></p>
<p class="p1"><em>If (v) is not answered and incorrect starting reagent is given in (vi), M1, M2 </em><em>and M3 may be scored but not M4 for either correct S</em><sub><span class="s1"><em>N</em></span></sub><em>1 or S</em><sub><span class="s1"><em>N</em></span></sub><em>2.</em></p>
<div class="question_part_label">a.vi.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">CH<sub><span class="s1">3</span></sub>COCH<sub><span class="s1">2</span></sub>CH<sub><span class="s1">3</span></sub>;</p>
<p class="p1"><em>Full or condensed structural formula may be given.</em></p>
<p class="p1"><em>For primary </em><strong><em>Z </em></strong><em>from (v), accept CH</em><sub><span class="s1"><em>3</em></span></sub><em>CH</em><sub><span class="s1"><em>2</em></span></sub><em>CH</em><sub><span class="s1"><em>2</em></span></sub><em>COOH/C</em><sub><span class="s1"><em>3</em></span></sub><em>H</em><sub><span class="s1"><em>7</em></span></sub><em>COOH but not </em><em>CH</em><sub><span class="s1"><em>3</em></span></sub><em>CH</em><sub><span class="s1"><em>2</em></span></sub><em>CH</em><sub><span class="s1"><em>2</em></span></sub><em>CHO.</em></p>
<p class="p1">ketone / alkanone;</p>
<div class="question_part_label">a.vii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">drawing of \({\text{RCOOR'}}\) group / <img src="images/Schermafbeelding_2016-09-23_om_13.44.48.png" alt="N12/4/CHEMI/SP2/ENG/TZ0/06.b.i_1/M"></p>
<p class="p1"><em>Allow C instead of R or \(R'\).</em></p>
<p class="p1"><em>Allow <img src="images/Schermafbeelding_2016-09-23_om_13.45.57.png" alt="N12/4/CHEMI/SP2/ENG/TZ0/06.b.i_2/M"></em></p>
<div class="question_part_label">b.i.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">\((100 - 62.0 - 10.4 = ){\text{ }}27.6\% {\text{ O}}\);</p>
<p class="p1">\({n_C}:\left( {\frac{{62.0}}{{12.01}} = } \right){\text{ }}5.162{\text{ (mol)}}\) <strong>and</strong> \({n_H}:\left( {\frac{{10.4}}{{1.01}} = } \right){\text{ }}10.297{\text{ (mol)}}\)</p>
<p class="p1"><strong>and</strong> \({n_O}:\left( {\frac{{27.6}}{{16.00}} = } \right){\text{ }}1.725{\text{ (mol)}}\);</p>
<p class="p1">dividing 5.162 and 10.297 by 1.725 (to get values \({{\text{C}}_{{\text{2.992}}}}{{\text{H}}_{{\text{5.969}}}}{{\text{O}}_{\text{1}}}\));</p>
<p class="p1">(empirical formula =) \({{\text{C}}_3}{{\text{H}}_6}{\text{O}}\);</p>
<p class="p1"><em>Award </em><strong><em>[4] </em></strong><em>for correct final answer if alternative method used.</em></p>
<p class="p1"><em>Allow integer values for atomic masses (i.e. 12, 1 and 16).</em></p>
<div class="question_part_label">b.ii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">C<sub>6</sub>H<sub>12</sub>O<sub>2</sub><span class="s1">;</span></p>
<div class="question_part_label">b.iii.</div>
</div>
<h2 style="margin-top: 1em">Examiners report</h2>
<div class="question" style="padding-left: 20px;">
<p class="p1">Meaning of the term <em>structural isomers </em>was well defined with the weaker candidates referring to similar instead of same molecular formula but different arrangement of atoms.</p>
<div class="question_part_label">a.ii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">Many candidates stated the IUPAC name of the isomers of C<sub><span class="s1">4</span></sub>H<sub><span class="s1">8 </span></sub>and deduced correctly the structural formulas of the two other isomers.</p>
<div class="question_part_label">a.iii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">Most candidates were able to write the chemical equation for the reaction of the isomer of C<sub><span class="s1">4</span></sub>H<sub><span class="s1">8 </span></sub>with HBr and identify the alcohol formed by the reaction of that product with NaOH.</p>
<div class="question_part_label">a.iv.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">In part (a) (v), the mechanisms proved a problem for majority of candidates.</p>
<div class="question_part_label">a.v.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">The use of curly arrows in reaction mechanisms continues to be poorly understood, the arrow often pointing in the wrong direction. Candidates must take care to accurately draw the position of the curly arrows illustrating the movement of electrons.</p>
<div class="question_part_label">a.vi.</div>
</div>
<div class="question" style="padding-left: 20px;">
[N/A]
<div class="question_part_label">a.vii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">In part (b), the ester functional group was drawn correctly and it was pleasing to see that the majority of candidates handled the calculation of the empirical and molecular formulas extremely well.</p>
<div class="question_part_label">b.i.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">In part (b), the ester functional group was drawn correctly and it was pleasing to see that the majority of candidates handled the calculation of the empirical and molecular formulas extremely well.</p>
<div class="question_part_label">b.ii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">In part (b), the ester functional group was drawn correctly and it was pleasing to see that the majority of candidates handled the calculation of the empirical and molecular formulas extremely well.</p>
<div class="question_part_label">b.iii.</div>
</div>
<br><hr><br><div class="specification">
<p class="p1">Chloroethene, C<sub><span class="s1">2</span></sub>H<sub><span class="s1">3</span></sub>Cl, is an important organic compound used to manufacture the polymer poly(chloroethene).</p>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">Draw the Lewis structure for chloroethene and predict the H–C–Cl bond angle.</p>
<div class="marks">[2]</div>
<div class="question_part_label">a.i.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">Draw a section of poly(chloroethene) containing six carbon atoms.</p>
<div class="marks">[1]</div>
<div class="question_part_label">a.ii.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">Outline why the polymerization of alkenes is of economic importance and why the disposal of plastics is a problem.</p>
<div class="marks">[2]</div>
<div class="question_part_label">a.iii.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">Chloroethene can be converted to ethanol in two steps. For each step deduce an overall equation for the reaction taking place.</p>
<p class="p1">Step 1:</p>
<p class="p1">Step 2:</p>
<div class="marks">[2]</div>
<div class="question_part_label">b.i.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">State the reagents and conditions necessary to prepare ethanoic acid from ethanol in the laboratory.</p>
<div class="marks">[2]</div>
<div class="question_part_label">b.ii.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">State an equation, including state symbols, for the reaction of ethanoic acid with water. Identify a Brønsted-Lowry acid in the equation and its conjugate base.</p>
<div class="marks">[3]</div>
<div class="question_part_label">b.iii.</div>
</div>
<h2 style="margin-top: 1em">Markscheme</h2>
<div class="question" style="padding-left: 20px;">
<p><img src="images/Schermafbeelding_2016-10-07_om_10.58.18.png" alt="M10/4/CHEMI/SP2/ENG/TZ1/03.a.i/M"> ;</p>
<p class="p1"><em>Accept lines, dots or crosses for electron pairs.</em></p>
<p class="p1"><em>Lone pairs required on chlorine.</em></p>
<p class="p1">(approximately) 120°;</p>
<p class="p1"><em>Accept any bond angle in the range 113–</em><em>120°</em>.</p>
<div class="question_part_label">a.i.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p><img src="images/Schermafbeelding_2016-10-07_om_11.04.14.png" alt="M10/4/CHEMI/SP2/ENG/TZ1/03.a.ii/M"> ;</p>
<p class="p1"><em>Brackets not required for mark.</em></p>
<p class="p1"><em>Continuation bonds from each carbon are required.</em></p>
<p class="p1"><em>Cl atoms can be above or below carbon spine or alternating above and below.</em></p>
<div class="question_part_label">a.ii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">plastics are cheap/versatile/a large industry / plastics have many uses / <em>OWTTE</em>;</p>
<p class="p1">plastics are not biodegradeable / plastics take up large amounts of space in landfill / pollution caused by burning of plastics / <em>OWTTE</em>;</p>
<p class="p1"><em>Do not accept plastics cause litter.</em></p>
<p class="p1"><em>Allow plastics don’t decompose quickly / OWTTE.</em></p>
<div class="question_part_label">a.iii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">(i) <span class="Apple-converted-space"> </span><em>Step 1:</em></p>
<p class="p1">\({\text{C}}{{\text{H}}_2}{\text{CHCl}} + {{\text{H}}_2} \to {\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{Cl}}\);</p>
<p class="p1"><em>Step 2:</em></p>
<p class="p1">\({\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{Cl}} + {\text{O}}{{\text{H}}^ - } \to {\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{OH}} + {\text{C}}{{\text{l}}^ - }\);</p>
<p class="p1"><em>Allow NaOH or NaCl etc. instead of OH</em><sup><span class="s1"><em>– </em></span></sup><em>and Cl</em><sup><span class="s1"><em>–</em></span></sup><em>.</em></p>
<p class="p1"><em>Allow abbreviated formulas C</em><sub><span class="s1"><em>2</em></span></sub><em>H</em><sub><span class="s1"><em>3</em></span></sub><em>Cl, C</em><sub><span class="s1"><em>2</em></span></sub><em>H</em><sub><span class="s1"><em>5</em></span></sub><em>Cl, C</em><sub><span class="s1"><em>2</em></span></sub><em>H</em><sub><span class="s1"><em>5</em></span></sub><em>OH.</em></p>
<div class="question_part_label">b.i.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">\({{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}\)/\({{\text{H}}^ + }\)/acidified <strong>and </strong>\({\text{C}}{{\text{r}}_{\text{2}}}{\text{O}}_{_{\text{7}}}^{2 - }\)/(potassium/sodium) dichromate;</p>
<p class="p1"><em>Accept suitable oxidizing agents (e.g. KMnO</em><sub><span class="s1"><em>4 </em></span></sub><em>etc.) but only with acid.</em></p>
<p class="p1"><em>Ignore missing or incorrect oxidation states in reagents.</em></p>
<p class="p1">(heat under) reflux;</p>
<p class="p1"><em>Second mark can be scored even if reagent is incorrect.</em></p>
<div class="question_part_label">b.ii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">\({\text{C}}{{\text{H}}_3}{\text{COOH(aq)}} + {{\text{H}}_2}{\text{O(l)}} \rightleftharpoons {\text{C}}{{\text{H}}_3}{\text{CO}}{{\text{O}}^ - }{\text{(aq)}} + {{\text{H}}_3}{{\text{O}}^ + }{\text{(aq)}}\)</p>
<p class="p1"><strong>OR</strong></p>
<p class="p1">\({\text{C}}{{\text{H}}_3}{\text{COOH(l)}} + {{\text{H}}_2}{\text{O(l)}} \rightleftharpoons {\text{C}}{{\text{H}}_3}{\text{CO}}{{\text{O}}^ - }{\text{(aq)}} + {{\text{H}}_3}{{\text{O}}^ + }{\text{(aq)}}\)</p>
<p class="p1"><strong>OR</strong></p>
<p class="p1">\({\text{C}}{{\text{H}}_3}{\text{COOH(aq)}} \rightleftharpoons {\text{C}}{{\text{H}}_3}{\text{CO}}{{\text{O}}^ - }{\text{(aq)}} + {{\text{H}}^ + }{\text{(aq)}}\)</p>
<p class="p1">correct equation;</p>
<p class="p1">state symbols <strong>and</strong> \( \rightleftharpoons \);</p>
<p class="p1">BL acid is \({\text{C}}{{\text{H}}_{\text{3}}}{\text{COOH}}\) and cb is \({\text{C}}{{\text{H}}_{\text{3}}}{\text{CO}}{{\text{O}}^ - }\) / BL acid is \({{\text{H}}_{\text{3}}}{{\text{O}}^ + }\) and cb is \({{\text{H}}_{\text{2}}}{\text{O}}\);</p>
<div class="question_part_label">b.iii.</div>
</div>
<h2 style="margin-top: 1em">Examiners report</h2>
<div class="question" style="padding-left: 20px;">
<p class="p1">The main G2 comments on this question related to the inclusion of organic chemistry in Section A. It should be noted that ANY Topic can be asked in Section A of P2, and there is no set-formula in relation to question setting. Organic chemistry is an integral part of the IB SL Chemistry programme, and is covered in Topic 10 of the guide (12 hours in total). Hence, candidates should be adequately prepared for questions on this topic, even in Section A. In 3(a), the Lewis structure of chlorethene was generally drawn correctly, though the weaker candidates often omitted the lone pairs on the chlorine. The bond angle was usually predicted, although right angles and 109.5°<span class="s1"> </span>were often given. Even some of the better candidates explained their choice of bond angle, based on the fact that the double bond occupies more space causing the HCCl bond angle to drop less than 120°.</p>
<div class="question_part_label">a.i.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">Many candidates gave double bonds and some forgot to include continuation bonds.</p>
<div class="question_part_label">a.ii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">The Aim 8 question in part (iii) was very well answered this session. Almost all candidates scored the disposal problem of plastics mark and many achieved the economics importance mark also.</p>
<div class="question_part_label">a.iii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">In general (b) was very poorly answered, again showing a clear weakness in organic chemistry, which is an area of major concern. (i) was poorly done. Candidates who managed a correct reaction for the first step often used water instead of hydroxide ion for the second step.</p>
<div class="question_part_label">b.i.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">In general (b) was very poorly answered, again showing a clear weakness in organic chemistry, which is an area of major concern. In (ii), candidates who mentioned dichromate(VI) or permanganate(VIII) often omitted the acid. In addition, reflux was often missing.</p>
<div class="question_part_label">b.ii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">In general (b) was very poorly answered, again showing a clear weakness in organic chemistry, which is an area of major concern. In (iii), very few candidates scored all three marks here, even though the question itself was easy. The equation was often correct, but the equilibrium arrow was rarely given. Some candidates did not know the formula for ethanoic acid which was surprising.</p>
<div class="question_part_label">b.iii.</div>
</div>
<br><hr><br><div class="specification">
<p class="p1">Consider the following sequence of reactions.</p>
<p class="p1">\[{\text{RC}}{{\text{H}}_3}\xrightarrow{{reaction 1}}{\text{RC}}{{\text{H}}_2}{\text{Br}}\xrightarrow{{reaction 2}}{\text{RC}}{{\text{H}}_2}{\text{OH}}\xrightarrow{{reaction 3}}{\text{RCOOH}}\]</p>
<p class="p1">\({\text{RC}}{{\text{H}}_{\text{3}}}\) is an unknown alkane in which R represents an alkyl group.</p>
</div>
<div class="specification">
<p class="p1">The mechanism in <em>reaction 2 </em>is described as S<sub><span class="s1">N</span></sub>2.</p>
</div>
<div class="specification">
<p class="p1">Propan-1-ol has two structural isomers.</p>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">The alkane contains 81.7% by mass of carbon. Determine its empirical formula, showing your working.</p>
<div class="marks">[3]</div>
<div class="question_part_label">a.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">Equal volumes of carbon dioxide and the unknown alkane are found to have the same mass, measured to an accuracy of two significant figures, at the same temperature and pressure. Deduce the molecular formula of the alkane.</p>
<div class="marks">[1]</div>
<div class="question_part_label">b.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">(i) <span class="Apple-converted-space"> </span>State the reagent and conditions needed for <em>reaction 1</em>.</p>
<p class="p1">(ii) <span class="Apple-converted-space"> </span>State the reagent(s) and conditions needed for <em>reaction 3</em>.</p>
<div class="marks">[2]</div>
<div class="question_part_label">c.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1"><em>Reaction 1 </em>involves a free-radical mechanism. Describe the stepwise mechanism, by giving equations to represent the initiation, propagation and termination steps.</p>
<div class="marks">[4]</div>
<div class="question_part_label">d.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">(i) <span class="Apple-converted-space"> </span>State the meaning of each of the symbols in S<sub><span class="s1">N</span></sub>2.</p>
<p class="p1">(ii) <span class="Apple-converted-space"> </span>Explain the mechanism of this reaction using curly arrows to show the movement of electron pairs, and draw the structure of the transition state.</p>
<div class="marks">[4]</div>
<div class="question_part_label">e.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">(i) <span class="Apple-converted-space"> </span>Deduce the structural formula of each isomer.</p>
<p class="p1">(ii) <span class="Apple-converted-space"> </span>Identify the isomer from part (f) (i) which has the higher boiling point and explain your choice. Refer to both isomers in your explanation.</p>
<div class="marks">[4]</div>
<div class="question_part_label">f.</div>
</div>
<h2 style="margin-top: 1em">Markscheme</h2>
<div class="question" style="padding-left: 20px;">
<p class="p1">\({{\text{n}}_{\text{C}}} = \frac{{81.7}}{{12.01}} = 6.80\) <strong>and</strong> \({{\text{n}}_{\text{H}}} = \frac{{18.3}}{{1.01}} = 18.1\);</p>
<p class="p1">ratio of 1: 2.67 /1: 2.7;</p>
<p class="p1">\({{\text{C}}_3}{{\text{H}}_8}\);</p>
<p class="p1"><em>No penalty for using 12 and 1</em>.</p>
<div class="question_part_label">a.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>\({{\text{C}}_{\text{3}}}{{\text{H}}_{\text{8}}}\);</p>
<div class="question_part_label">b.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">(i) <span class="Apple-converted-space"> </span>\({\text{B}}{{\text{r}}_2}\) /bromine;</p>
<p class="p1">UV/ultraviolet light;</p>
<p class="p1"><em>Accept hf/hv/sunlight</em>.</p>
<p class="p1">(ii) <span class="Apple-converted-space"> </span>\({\text{C}}{{\text{r}}_2}{\text{O}}_7^{2 - }\) / \({\text{MnO}}_4^ - \) <strong>and </strong>acidified/\({{\text{H}}^ + }\) /\({{\text{H}}_3}{{\text{O}}^ + }\);</p>
<p class="p1"><em>Accept names</em>.</p>
<p class="p1">heat / reflux;</p>
<div class="question_part_label">c.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p><em>initiation:</em></p>
<p>\({\text{B}}{{\text{r}}_2} \to 2{\text{Br}} \bullet \);</p>
<p><em>propagation:</em></p>
<p>\({\text{Br}} \bullet + {\text{RC}}{{\text{H}}_3} \to {\text{HBr}} + {\text{RC}}{{\text{H}}_2} \bullet \);</p>
<p>\({\text{RC}}{{\text{H}}_2} \bullet + {\text{B}}{{\text{r}}_2} \to {\text{RC}}{{\text{H}}_2}{\text{Br}} + {\text{Br}} \bullet \);</p>
<p><em>termination:</em></p>
<p>\({\text{Br}} \bullet + {\text{Br}} \bullet \to {\text{B}}{{\text{r}}_2}\);</p>
<p>\({\text{RC}}{{\text{H}}_2} \bullet + {\text{Br}} \bullet \to {\text{RC}}{{\text{H}}_2}{\text{Br}}\);</p>
<p>\({\text{RC}}{{\text{H}}_2} \bullet + {\text{RC}}{{\text{H}}_2} \bullet \to {\text{RC}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{R}}\);</p>
<p><em>Award </em><strong><em>[1] </em></strong><em>for any termination step</em>.</p>
<p><em>Accept radical with or without </em>\( \bullet \) <em>throughout.</em></p>
<p><em>Do not penalise the use of an incorrect alkane in the mechanism.</em></p>
<div class="question_part_label">d.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">(i) <span class="Apple-converted-space"> </span>substitution <strong>and </strong>nucleophilic <strong>and </strong>bimolecular/two species in rate-determining step;</p>
<p class="p1"><em>Allow second order in place of bimolecular.</em></p>
<p class="p1">(ii) <span class="Apple-converted-space"> <img src="images/Schermafbeelding_2016-09-30_om_07.25.27.png" alt="N10/4/CHEMI/SP2/ENG/TZ0/05.e/M"></span></p>
<p class="p1">curly arrow going from lone pair/negative charge on O in OH<sup><span class="s1">– </span></sup>to C;</p>
<p class="p1"><em>Do not allow curly arrow originating on H in OH</em><sup><span class="s1"><em>–</em></span></sup><em>.</em></p>
<p class="p1">curly arrow showing Br leaving;</p>
<p class="p1"><em>Accept curly arrow either going from bond between C and Br to Br in bromoethane or in the transition state.</em></p>
<p class="p1">representation of transition state showing negative charge, square brackets and partial bonds;</p>
<p class="p1"><em>Do not penalize if HO and Br are not at 180</em><span class="s1"><em>o </em></span><em>to each other.</em></p>
<p class="p1"><em>Do not award M3 if OH----C bond is represented unless already penalised in M1.</em></p>
<p class="p1"><em>Do not penalise the use of an incorrect alkyl chain in the mechanism.</em></p>
<div class="question_part_label">e.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">(i) <span class="Apple-converted-space"> </span>\({\text{C}}{{\text{H}}_3}{\text{OC}}{{\text{H}}_2}{\text{C}}{{\text{H}}_3}\);</p>
<p class="p1">\({\text{C}}{{\text{H}}_3}{\text{CHOHC}}{{\text{H}}_3}\);</p>
<p class="p1"><em>Allow more detailed structural formulas.</em></p>
<p class="p1">(ii) <span class="Apple-converted-space"> </span>\({\text{C}}{{\text{H}}_3}{\text{CHOHC}}{{\text{H}}_3}\) has higher boiling point due to hydrogen bonding;</p>
<p class="p1">\({\text{C}}{{\text{H}}_3}{\text{OC}}{{\text{H}}_2}{\text{C}}{{\text{H}}_3}\) has lower boiling point due to Van der Waals’/London/dispersion/dipole-dipole forces;</p>
<p class="p1">Hydrogen bonds in \({\text{C}}{{\text{H}}_3}{\text{CHOHC}}{{\text{H}}_3}\) are stronger;</p>
<p class="p1"><em>Allow ecf if wrong structures suggested.</em></p>
<div class="question_part_label">f.</div>
</div>
<h2 style="margin-top: 1em">Examiners report</h2>
<div class="question" style="padding-left: 20px;">
<p class="p1">This was the least popular question in Section B but there was a generally pleasing level of performance. Most candidates scored at least 2 out of 3 marks for calculating the empirical formula. Several candidates correctly worked out the ratio but then rounded 2.7 to 3 to give an incorrect empirical formula of \({\text{C}}{{\text{H}}_{\text{3}}}\) instead of \({{\text{C}}_{\text{3}}}{{\text{H}}_{\text{8}}}\).</p>
<div class="question_part_label">a.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">Many did manage to calculate a correct molecular formula even though their empirical formula was incorrect.</p>
<div class="question_part_label">b.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">Free radical substitution was well known, however, there was some confusion about whether the reagent was supposed to be Br<sub><span class="s1">2</span></sub>(g), Br<sub><span class="s1">2</span></sub>(aq) or Br<sub><span class="s1">2 </span></sub>in CCl<sub><span class="s1">4</span></sub>. Most stated that UV was required.</p>
<div class="question_part_label">c.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">In 5(d) most candidates scored at least 3 marks out of 4. A few used Cl<sub><span class="s1">2 </span></sub>instead of Br<sub><span class="s1">2</span></sub>.</p>
<div class="question_part_label">d.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">Most knew the meaning of the symbols S<sub><span class="s1">N</span></sub>2, however, a few did not correctly state the meaning of the 2. The mechanism caused some problems and some of the common errors here were drawing the curly arrow from the H; forgetting to include any curly arrow to show Br leaving; writing the partial bond from the nucleophile as OH---C; or missing the negative charge from the transition state. Unfortunately, most candidates had a combination of these errors. Also, in most cases the partial bonds were drawn at angles less than 180 degrees which, although not penalised, is totally incorrect as attack by the nucleophile must be on the opposite side to the halogen leaving.</p>
<div class="question_part_label">e.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">Part (f) proved to be very confusing for many candidates. The structural isomers of propan-1-ol were commonly drawn as propan-1-ol and propan-2-ol, which then caused enormous difficulties in 5(f)(ii) when they had to identify the isomer with the higher boiling point.</p>
<p class="p1">Those who were relying on ECF marks here often predicted the wrong isomer or found it very difficult to explain their prediction. The few candidates who drew the isomers correctly as an ether and an alcohol were generally able to score full marks by predicting and explaining the different boiling points.</p>
<div class="question_part_label">f.</div>
</div>
<br><hr><br><div class="specification">
<p>Alkenes, such as <strong>A</strong> (shown below), are important intermediates in the petrochemical industry because they undergo addition reactions to produce a wide variety of products, such as the conversion shown below.</p>
<p style="text-align: center;"><img src="images/Schermafbeelding_2016-08-17_om_17.00.19.png" alt="M14/4/CHEMI/SP2/ENG/TZ2/06"></p>
</div>
<div class="specification">
<p>Another way to make <strong>B</strong> is the reaction shown below.</p>
<p><img src="images/Schermafbeelding_2016-08-17_om_17.11.56.png" alt="M14/4/CHEMI/SP2/ENG/TZ2/06.c"></p>
</div>
<div class="specification">
<p><strong>B </strong>can be converted into <strong>C</strong>.</p>
<p style="text-align: center;"><img src="images/Schermafbeelding_2016-08-17_om_17.16.54.png" alt="M14/4/CHEMI/SP2/ENG/TZ2/06.d"></p>
</div>
<div class="specification">
<p>In the gas phase, <strong>A</strong> reacts with hydrogen to form <strong>D</strong>.</p>
<p style="text-align: center;"><img src="images/Schermafbeelding_2016-08-17_om_17.41.44.png" alt="M14/4/CHEMI/SP2/ENG/TZ2/06.g"></p>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Applying IUPAC rules, state the name of <strong>A</strong>.</p>
<div class="marks">[1]</div>
<div class="question_part_label">a.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>State the reagent required to convert <strong>A</strong> into <strong>B</strong>.</p>
<div class="marks">[1]</div>
<div class="question_part_label">b.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>(i) State the conditions required for this reaction to occur.</p>
<p> </p>
<p>(ii) Outline why it would give a poor yield of the desired product.</p>
<div class="marks">[2]</div>
<div class="question_part_label">c.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>(i) State the reagent required.</p>
<p> </p>
<p>(ii) Explain the mechanism of this reaction, using curly arrows to represent the movement of electron pairs.</p>
<div class="marks">[4]</div>
<div class="question_part_label">d.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p><strong>A </strong>can also be converted into <strong>C </strong>without going via <strong>B</strong>. State the reagent and conditions required.</p>
<div class="marks">[2]</div>
<div class="question_part_label">e.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>(i) State why <strong>C </strong>is <strong>not </strong>readily oxidized by acidified potassium dichromate(VI).</p>
<p> </p>
<p> </p>
<p>(ii) Deduce the structural formula of an isomer of <strong>C </strong>that could be oxidized to a carboxylic acid by this reagent.</p>
<div class="marks">[2]</div>
<div class="question_part_label">f.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>State the conditions required for this reaction to occur.</p>
<div class="marks">[1]</div>
<div class="question_part_label">g.i.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>State the homologous series to which <strong>D</strong> belongs.</p>
<div class="marks">[1]</div>
<div class="question_part_label">g.ii.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Determine the enthalpy change, in \({\text{kJ}}\,{\text{mo}}{{\text{l}}^{ - 1}}\), for the reaction of <strong>A</strong> with hydrogen, using Table 10 of the Data Booklet, and state whether the reaction is exothermic or endothermic.</p>
<div class="marks">[4]</div>
<div class="question_part_label">g.iii.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>The standard enthalpy change of combustion of <strong>A</strong> is \( - 4000{\text{ kJ}}\,{\text{mo}}{{\text{l}}^{ - 1}}\). Calculate the amount of <strong>A</strong>, in mol, that would have to be burned to raise the temperature of \({\text{1 d}}{{\text{m}}^{\text{3}}}\) of water from 20 °C to 100 °C.</p>
<div class="marks">[2]</div>
<div class="question_part_label">g.iv.</div>
</div>
<h2 style="margin-top: 1em">Markscheme</h2>
<div class="question" style="padding-left: 20px;">
<p>2,3-dimethylbut-2-ene;</p>
<p><em>Ignore punctuation.</em></p>
<div class="question_part_label">a.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>hydrogen bromide / hydrobromic acid / HBr;</p>
<div class="question_part_label">b.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>(i) ultraviolet light/sunlight;</p>
<p><em>Accept “<span style="text-decoration: underline;">very high</span> temperature”.</em></p>
<p>(ii) random/further/multiple substitution (so low probability of desired product) / would give a mixture of many different products / <em>OWTTE</em>;</p>
<div class="question_part_label">c.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>(i) (aqueous) sodium hydroxide/NaOH / potassium hydroxide/KOH;</p>
<p><em>Accept hydroxide ion/OH</em><sup><em>–</em></sup><em>.</em></p>
<p>(ii) <img src="images/Schermafbeelding_2016-08-17_om_17.20.52.png" alt="M14/4/CHEMI/SP2/ENG/TZ2/06.d.ii/M"></p>
<p>\({S_N}1\):</p>
<p>curly arrow from C–Br bond showing Br leaving;</p>
<p>representation of tertiary carbocation;</p>
<p>curly arrow going from lone pair/negative charge on O in \({\text{H}}{{\text{O}}^ - }\) to \({{\text{C}}^ + }\);</p>
<p><em>Do not allow arrow originating on H in HO</em><sup><em>–</em></sup><em>.</em></p>
<p><em>Award </em><strong><em>[2] </em></strong><em>for perfect S</em><sub><em>N</em></sub><em>2 mechanism.</em></p>
<p><em>Award </em><strong><em>[1] </em></strong><em>for S</em><sub><em>N</em></sub><em>2 mechanism with minor mistakes.</em></p>
<div class="question_part_label">d.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>water / steam;</p>
<p>heat and acid catalyst /<em>(concentrated) </em>\({{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}/{{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_{\text{4}}}\);</p>
<div class="question_part_label">e.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>(i) (it is a) tertiary/3° alcohol / carbon of C–OH is not bonded to a hydrogen;</p>
<p><em>Accept “it is not a primary or secondary alcohol”.</em></p>
<p>(ii) any \({{\text{C}}_6}{{\text{H}}_{14}}{\text{O}}\) primary alcohol / \({{\text{C}}_5}{{\text{H}}_{11}}{\text{C}}{{\text{H}}_2}{\text{OH}}\);</p>
<div class="question_part_label">f.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>Ni/Pt/Pd catalyst;</p>
<div class="question_part_label">g.i.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>alkanes;</p>
<div class="question_part_label">g.ii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p><em>bonds broken:</em> (E(C=C) + E(H–H) = 612 + 436 =) \({\text{1048 (kJ}}\,{\text{mo}}{{\text{l}}^{ - 1}}{\text{)}}\);</p>
<p><em>Accept (6956 + 436 =) 7392 if all bonds in alkene broken.</em></p>
<p><em>bonds formed: </em>E(C–C) + 2 \( \times \) E(C–H) = 347 + (2 \( \times \) 413) = \({\text{1173 (kJ}}\,{\text{mo}}{{\text{l}}^{ - 1}}{\text{)}}\);</p>
<p><em>Accept 7517 if all the bonds in the product are summed.</em></p>
<p>\(\Delta H = 1048 - 1173/7392 - 7517 = - 125{\text{ (kJ}}\,{\text{mo}}{{\text{l}}^{ - 1}}{\text{)}}\);</p>
<p><em>Award </em><strong><em>[3] </em></strong><em>for correct final answer.</em></p>
<p><em>Award </em><strong><em>[2] </em></strong><em>for +125.</em></p>
<p>exothermic;</p>
<p><em>Apply ECF if sign of </em>\(\Delta H\)<em> incorrect.</em></p>
<p><em>Do not award a mark for “exothermic” if </em>\(\Delta H\)<em> given as positive.</em></p>
<div class="question_part_label">g.iii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>energy required to heat water \(\left( { = m \times s \times \Delta T = 1 \times 4.18 \times (100 - 20)} \right) = 334.4{\text{ }}({\text{kJ}})\);</p>
<p><em>Ignore sign of energy change.</em></p>
<p>amount required \(\frac{{334.4}}{{4000}} = 0.0836{\text{ (mol)}}\);</p>
<p><em>Award </em><strong><em>[2] </em></strong><em>for correct final answer.</em></p>
<div class="question_part_label">g.iv.</div>
</div>
<h2 style="margin-top: 1em">Examiners report</h2>
<div class="question" style="padding-left: 20px;">
<p>Probably the most popular and successfully answered. Most students were family with IUPAC nomenclature and realised that UV radiation is required to initiate the halogenation of an alkane, though fewer realised that the much greater probability of forming a different isomer, or the problem of polysubstitution would result in a very low yield. The conditions for the hydrolysis of the bromoalkane were well known, though fewer recognised it as a tertiary halogenoalkane and described the \({{\text{S}}_{\text{N}}}{\text{1}}\) reaction mechanism. Only a small number of candidates were able to show the electron pair originating from C–Br bond or the lone pair on the oxygen or negative charge of the hydroxide ion. Many candidates knew that tertiary alcohols could not be oxidised and correctly drew primary structures for alcohols that could be oxidised to carboxylic acids although some made careless errors and drew secondary structures or did not answer the question and proposed aldehydes. Many candidates were able to determine the enthalpy change, from bond enthalpies but some had not read the question carefully and did not address the final mark. A significant number of candidates made small errors but still gained ECF marks as they had set their working out clearly. The calculation of the amount of fuel required to raise the temperature proved more difficult with many students overlooking the volume of water and using the data to calculate the mass of the hydrocarbon that would be heated by 80 °C by the molar enthalpy of combustion and using the specific heat capacity of water.</p>
<div class="question_part_label">a.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>Probably the most popular and successfully answered. Most students were family with IUPAC nomenclature and realised that UV radiation is required to initiate the halogenation of an alkane, though fewer realised that the much greater probability of forming a different isomer, or the problem of polysubstitution would result in a very low yield. The conditions for the hydrolysis of the bromoalkane were well known, though fewer recognised it as a tertiary halogenoalkane and described the \({{\text{S}}_{\text{N}}}{\text{1}}\) reaction mechanism. Only a small number of candidates were able to show the electron pair originating from C–Br bond or the lone pair on the oxygen or negative charge of the hydroxide ion. Many candidates knew that tertiary alcohols could not be oxidised and correctly drew primary structures for alcohols that could be oxidised to carboxylic acids although some made careless errors and drew secondary structures or did not answer the question and proposed aldehydes. Many candidates were able to determine the enthalpy change, from bond enthalpies but some had not read the question carefully and did not address the final mark. A significant number of candidates made small errors but still gained ECF marks as they had set their working out clearly. The calculation of the amount of fuel required to raise the temperature proved more difficult with many students overlooking the volume of water and using the data to calculate the mass of the hydrocarbon that would be heated by 80 °C by the molar enthalpy of combustion and using the specific heat capacity of water.</p>
<div class="question_part_label">b.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>Probably the most popular and successfully answered. Most students were family with IUPAC nomenclature and realised that UV radiation is required to initiate the halogenation of an alkane, though fewer realised that the much greater probability of forming a different isomer, or the problem of polysubstitution would result in a very low yield. The conditions for the hydrolysis of the bromoalkane were well known, though fewer recognised it as a tertiary halogenoalkane and described the \({{\text{S}}_{\text{N}}}{\text{1}}\) reaction mechanism. Only a small number of candidates were able to show the electron pair originating from C–Br bond or the lone pair on the oxygen or negative charge of the hydroxide ion. Many candidates knew that tertiary alcohols could not be oxidised and correctly drew primary structures for alcohols that could be oxidised to carboxylic acids although some made careless errors and drew secondary structures or did not answer the question and proposed aldehydes. Many candidates were able to determine the enthalpy change, from bond enthalpies but some had not read the question carefully and did not address the final mark. A significant number of candidates made small errors but still gained ECF marks as they had set their working out clearly. The calculation of the amount of fuel required to raise the temperature proved more difficult with many students overlooking the volume of water and using the data to calculate the mass of the hydrocarbon that would be heated by 80 °C by the molar enthalpy of combustion and using the specific heat capacity of water.</p>
<div class="question_part_label">c.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>Probably the most popular and successfully answered. Most students were family with IUPAC nomenclature and realised that UV radiation is required to initiate the halogenation of an alkane, though fewer realised that the much greater probability of forming a different isomer, or the problem of polysubstitution would result in a very low yield. The conditions for the hydrolysis of the bromoalkane were well known, though fewer recognised it as a tertiary halogenoalkane and described the \({{\text{S}}_{\text{N}}}{\text{1}}\) reaction mechanism. Only a small number of candidates were able to show the electron pair originating from C–Br bond or the lone pair on the oxygen or negative charge of the hydroxide ion. Many candidates knew that tertiary alcohols could not be oxidised and correctly drew primary structures for alcohols that could be oxidised to carboxylic acids although some made careless errors and drew secondary structures or did not answer the question and proposed aldehydes. Many candidates were able to determine the enthalpy change, from bond enthalpies but some had not read the question carefully and did not address the final mark. A significant number of candidates made small errors but still gained ECF marks as they had set their working out clearly. The calculation of the amount of fuel required to raise the temperature proved more difficult with many students overlooking the volume of water and using the data to calculate the mass of the hydrocarbon that would be heated by 80 °C by the molar enthalpy of combustion and using the specific heat capacity of water.</p>
<div class="question_part_label">d.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>Probably the most popular and successfully answered. Most students were family with IUPAC nomenclature and realised that UV radiation is required to initiate the halogenation of an alkane, though fewer realised that the much greater probability of forming a different isomer, or the problem of polysubstitution would result in a very low yield. The conditions for the hydrolysis of the bromoalkane were well known, though fewer recognised it as a tertiary halogenoalkane and described the \({{\text{S}}_{\text{N}}}{\text{1}}\) reaction mechanism. Only a small number of candidates were able to show the electron pair originating from C–Br bond or the lone pair on the oxygen or negative charge of the hydroxide ion. Many candidates knew that tertiary alcohols could not be oxidised and correctly drew primary structures for alcohols that could be oxidised to carboxylic acids although some made careless errors and drew secondary structures or did not answer the question and proposed aldehydes. Many candidates were able to determine the enthalpy change, from bond enthalpies but some had not read the question carefully and did not address the final mark. A significant number of candidates made small errors but still gained ECF marks as they had set their working out clearly. The calculation of the amount of fuel required to raise the temperature proved more difficult with many students overlooking the volume of water and using the data to calculate the mass of the hydrocarbon that would be heated by 80 °C by the molar enthalpy of combustion and using the specific heat capacity of water.</p>
<div class="question_part_label">e.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>Probably the most popular and successfully answered. Most students were family with IUPAC nomenclature and realised that UV radiation is required to initiate the halogenation of an alkane, though fewer realised that the much greater probability of forming a different isomer, or the problem of polysubstitution would result in a very low yield. The conditions for the hydrolysis of the bromoalkane were well known, though fewer recognised it as a tertiary halogenoalkane and described the \({{\text{S}}_{\text{N}}}{\text{1}}\) reaction mechanism. Only a small number of candidates were able to show the electron pair originating from C–Br bond or the lone pair on the oxygen or negative charge of the hydroxide ion. Many candidates knew that tertiary alcohols could not be oxidised and correctly drew primary structures for alcohols that could be oxidised to carboxylic acids although some made careless errors and drew secondary structures or did not answer the question and proposed aldehydes. Many candidates were able to determine the enthalpy change, from bond enthalpies but some had not read the question carefully and did not address the final mark. A significant number of candidates made small errors but still gained ECF marks as they had set their working out clearly. The calculation of the amount of fuel required to raise the temperature proved more difficult with many students overlooking the volume of water and using the data to calculate the mass of the hydrocarbon that would be heated by 80 °C by the molar enthalpy of combustion and using the specific heat capacity of water.</p>
<div class="question_part_label">f.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>Probably the most popular and successfully answered. Most students were family with IUPAC nomenclature and realised that UV radiation is required to initiate the halogenation of an alkane, though fewer realised that the much greater probability of forming a different isomer, or the problem of polysubstitution would result in a very low yield. The conditions for the hydrolysis of the bromoalkane were well known, though fewer recognised it as a tertiary halogenoalkane and described the \({{\text{S}}_{\text{N}}}{\text{1}}\) reaction mechanism. Only a small number of candidates were able to show the electron pair originating from C–Br bond or the lone pair on the oxygen or negative charge of the hydroxide ion. Many candidates knew that tertiary alcohols could not be oxidised and correctly drew primary structures for alcohols that could be oxidised to carboxylic acids although some made careless errors and drew secondary structures or did not answer the question and proposed aldehydes. Many candidates were able to determine the enthalpy change, from bond enthalpies but some had not read the question carefully and did not address the final mark. A significant number of candidates made small errors but still gained ECF marks as they had set their working out clearly. The calculation of the amount of fuel required to raise the temperature proved more difficult with many students overlooking the volume of water and using the data to calculate the mass of the hydrocarbon that would be heated by 80 °C by the molar enthalpy of combustion and using the specific heat capacity of water.</p>
<div class="question_part_label">g.i.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>Probably the most popular and successfully answered. Most students were family with IUPAC nomenclature and realised that UV radiation is required to initiate the halogenation of an alkane, though fewer realised that the much greater probability of forming a different isomer, or the problem of polysubstitution would result in a very low yield. The conditions for the hydrolysis of the bromoalkane were well known, though fewer recognised it as a tertiary halogenoalkane and described the \({{\text{S}}_{\text{N}}}{\text{1}}\) reaction mechanism. Only a small number of candidates were able to show the electron pair originating from C–Br bond or the lone pair on the oxygen or negative charge of the hydroxide ion. Many candidates knew that tertiary alcohols could not be oxidised and correctly drew primary structures for alcohols that could be oxidised to carboxylic acids although some made careless errors and drew secondary structures or did not answer the question and proposed aldehydes. Many candidates were able to determine the enthalpy change, from bond enthalpies but some had not read the question carefully and did not address the final mark. A significant number of candidates made small errors but still gained ECF marks as they had set their working out clearly. The calculation of the amount of fuel required to raise the temperature proved more difficult with many students overlooking the volume of water and using the data to calculate the mass of the hydrocarbon that would be heated by 80 °C by the molar enthalpy of combustion and using the specific heat capacity of water.</p>
<div class="question_part_label">g.ii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>Probably the most popular and successfully answered. Most students were family with IUPAC nomenclature and realised that UV radiation is required to initiate the halogenation of an alkane, though fewer realised that the much greater probability of forming a different isomer, or the problem of polysubstitution would result in a very low yield. The conditions for the hydrolysis of the bromoalkane were well known, though fewer recognised it as a tertiary halogenoalkane and described the \({{\text{S}}_{\text{N}}}{\text{1}}\) reaction mechanism. Only a small number of candidates were able to show the electron pair originating from C–Br bond or the lone pair on the oxygen or negative charge of the hydroxide ion. Many candidates knew that tertiary alcohols could not be oxidised and correctly drew primary structures for alcohols that could be oxidised to carboxylic acids although some made careless errors and drew secondary structures or did not answer the question and proposed aldehydes. Many candidates were able to determine the enthalpy change, from bond enthalpies but some had not read the question carefully and did not address the final mark. A significant number of candidates made small errors but still gained ECF marks as they had set their working out clearly. The calculation of the amount of fuel required to raise the temperature proved more difficult with many students overlooking the volume of water and using the data to calculate the mass of the hydrocarbon that would be heated by 80 °C by the molar enthalpy of combustion and using the specific heat capacity of water.</p>
<div class="question_part_label">g.iii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>Probably the most popular and successfully answered. Most students were family with IUPAC nomenclature and realised that UV radiation is required to initiate the halogenation of an alkane, though fewer realised that the much greater probability of forming a different isomer, or the problem of polysubstitution would result in a very low yield. The conditions for the hydrolysis of the bromoalkane were well known, though fewer recognised it as a tertiary halogenoalkane and described the \({{\text{S}}_{\text{N}}}{\text{1}}\) reaction mechanism. Only a small number of candidates were able to show the electron pair originating from C–Br bond or the lone pair on the oxygen or negative charge of the hydroxide ion. Many candidates knew that tertiary alcohols could not be oxidised and correctly drew primary structures for alcohols that could be oxidised to carboxylic acids although some made careless errors and drew secondary structures or did not answer the question and proposed aldehydes. Many candidates were able to determine the enthalpy change, from bond enthalpies but some had not read the question carefully and did not address the final mark. A significant number of candidates made small errors but still gained ECF marks as they had set their working out clearly. The calculation of the amount of fuel required to raise the temperature proved more difficult with many students overlooking the volume of water and using the data to calculate the mass of the hydrocarbon that would be heated by 80 °C by the molar enthalpy of combustion and using the specific heat capacity of water.</p>
<div class="question_part_label">g.iv.</div>
</div>
<br><hr><br>