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</div><h2>SL Paper 2</h2><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>Electrolysis is an important industrial process used to obtain very reactive elements from their common ores.</p>
</div>
<div class="specification">
<p>Molten magnesium chloride can be electrolysed using inert graphite electrodes at 800 °C.</p>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Describe, using a labelled diagram, the essential components of this electrolytic cell.</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 align="LEFT">Molten magnesium chloride can be electrolysed using inert graphite electrodes at 800 °C.</p>
<p>Deduce the half-equations, including state symbols, for the reactions occurring at each electrode. (The melting points of MgCl<sub>2</sub> and Mg are 714 °C and 649 °C respectively.)</p>
<p> </p>
<p>Positive electrode (anode):</p>
<p> </p>
<p>Negative electrode (cathode):</p>
<div class="marks">[3]</div>
<div class="question_part_label">a.ii.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Outline why solid magnesium chloride does not conduct electricity.</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>Aluminium can also be obtained by electrolysis. Suggest <strong>one </strong>reason why aluminium is often used instead of iron by engineers.</p>
<div class="marks">[1]</div>
<div class="question_part_label">c.</div>
</div>
<h2 style="margin-top: 1em">Markscheme</h2>
<div class="question" style="padding-left: 20px;">
<p><em>Cell showing:</em></p>
<p><img src="images/Schermafbeelding_2016-08-10_om_05.30.29.png" alt="M15/4/CHEMI/SP2/ENG/TZ2/03.a.i/M"></p>
<p>molten electrolyte/MgCl<sub>2</sub>(l), electrodes <strong>and </strong>battery/DC supply; </p>
<p>correct labelling of positive electrode/anode/+ <strong>and </strong>negative electrode/cathode/–;</p>
<div class="question_part_label">a.i.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p><em>Positive electrode (anode):</em></p>
<p>\(2{\text{C}}{{\text{l}}^ - }{\text{(l)}} \to {\text{C}}{{\text{l}}_2}{\text{(g)}} + 2{{\text{e}}^ - }/{\text{C}}{{\text{l}}^ - }{\text{(l)}} \to \frac{1}{2}{\text{C}}{{\text{l}}_2}{\text{(g)}} + {{\text{e}}^ - }\);</p>
<p><em>Negative electrode (cathode):</em></p>
<p>\({\text{M}}{{\text{g}}^{2 + }}{\text{(l)}} + 2{{\text{e}}^ - } \to {\text{Mg(l)}}\);</p>
<p><em>Accept e instead of e</em><em><sup>–</sup></em><em>.</em></p>
<p><em>Award </em><strong><em>[1 max] </em></strong><em>for correct half-equations given at the wrong electrode.</em></p>
<p><em>Penalize use of reversible arrows once only.</em></p>
<p>correct state symbols in both equations;</p>
<div class="question_part_label">a.ii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>ions are not free to move when solid / ions in rigid lattice / <em>OWTTE</em>;</p>
<div class="question_part_label">b.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>aluminium/Al is less dense (compared to iron/Fe) / Al is more ductile or malleable/ aluminium forms a protective oxide layer / Al does not corrode / iron/Fe rusts /<em>OWTTE</em>;</p>
<p><em>Do not accept “A</em>l <em>is lighter” OR “less expensive” OR “A</em>l <em>can be recycled”.</em></p>
<div class="question_part_label">c.</div>
</div>
<h2 style="margin-top: 1em">Examiners report</h2>
<div class="question" style="padding-left: 20px;">
<p>There were very few carefully drawn correct diagrams as well as too many diagrams showing half-cells. The importance of the solution being molten was not appreciated. The equations did pick up marks, but it was extremely rare for candidates to access the mark for the correct state symbols. Far too many associated electrical conductivity in molten compounds with mobile electrons. The awareness that mobile ions are responsible for conductivity was poorly understood. The difference between "lightness" and density is still confused.</p>
<div class="question_part_label">a.i.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>There were very few carefully drawn correct diagrams as well as too many diagrams showing half-cells. The importance of the solution being molten was not appreciated. The equations did pick up marks, but it was extremely rare for candidates to access the mark for the correct state symbols. Far too many associated electrical conductivity in molten compounds with mobile electrons. The awareness that mobile ions are responsible for conductivity was poorly understood. The difference between "lightness" and density is still confused.</p>
<div class="question_part_label">a.ii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>There were very few carefully drawn correct diagrams as well as too many diagrams showing half-cells. The importance of the solution being molten was not appreciated. The equations did pick up marks, but it was extremely rare for candidates to access the mark for the correct state symbols. Far too many associated electrical conductivity in molten compounds with mobile electrons. The awareness that mobile ions are responsible for conductivity was poorly understood. The difference between "lightness" and density is still confused.</p>
<div class="question_part_label">b.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>There were very few carefully drawn correct diagrams as well as too many diagrams showing half-cells. The importance of the solution being molten was not appreciated. The equations did pick up marks, but it was extremely rare for candidates to access the mark for the correct state symbols. Far too many associated electrical conductivity in molten compounds with mobile electrons. The awareness that mobile ions are responsible for conductivity was poorly understood. The difference between "lightness" and density is still confused.</p>
<div class="question_part_label">c.</div>
</div>
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