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</div><h2>SL Paper 2</h2><div class="specification">
<p>Boron is most often encountered as a component in borosilicate glass (heat resistant glass).</p>
<p>The naturally occurring element contains two stable isotopes, \(_{\;{\text{5}}}^{{\text{10}}}{\text{B}}\) and \(_{\;{\text{5}}}^{{\text{11}}}{\text{B}}\).</p>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>State the number of protons, neutrons and electrons in an atom of \(_{\;{\text{5}}}^{{\text{11}}}{\text{B}}\).</p>
<p style="text-align: center;"><img src="images/Schermafbeelding_2016-08-17_om_08.42.37.png" alt="M14/4/CHEMI/SP2/ENG/TZ2/02.a"></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>The relative atomic mass of boron is 10.8, to three significant figures. Calculate the percentage of \(_{\;{\text{5}}}^{{\text{10}}}{\text{B}}\) in the naturally occurring element.</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>Isotopes of boron containing 7 and 8 neutrons also exist. Suggest why releasing isotopes containing more neutrons than the stable isotope into the environment can be dangerous.</p>
<div class="marks">[1]</div>
<div class="question_part_label">c.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>(i) State the formula of the compound that boron forms with fluorine.</p>
<p> </p>
<p>(ii) Explain why this compound acts as a Lewis acid.</p>
<div class="marks">[3]</div>
<div class="question_part_label">d.</div>
</div>
<br><hr><br><div class="specification">
<p class="p1">Ammonia, \({\text{N}}{{\text{H}}_{\text{3}}}\), is a base according to both the Brønsted–Lowry and the Lewis theories of acids and bases.</p>
</div>
<div class="specification">
<p class="p1">The equation for the reaction between sodium hydroxide, NaOH, and nitric acid, \({\text{HN}}{{\text{O}}_{\text{3}}}\), is shown below.</p>
<p class="p1">\[\begin{array}{*{20}{l}} {{\text{NaOH(aq)}} + {\text{HN}}{{\text{O}}_3}{\text{(aq)}} \to {\text{NaN}}{{\text{O}}_3}{\text{(aq)}} + {{\text{H}}_2}{\text{O(l)}}}&{{\text{ }}\Delta H = - 57.6{\text{ kJ}}\,{\text{mo}}{{\text{l}}^{ - 1}}} \end{array}\]</p>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">Distinguish between the terms <em>strong base </em>and <em>weak base</em>, and state one example of each.</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">State the equation for the reaction of ammonia with water.</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">Explain why ammonia can act as a Brønsted–Lowry base.</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">Explain why ammonia can also act as a Lewis base.</p>
<div class="marks">[1]</div>
<div class="question_part_label">b.iii.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">(i) <span class="Apple-converted-space"> </span>When ammonium chloride, \({\text{N}}{{\text{H}}_{\text{4}}}{\text{Cl(aq)}}\), is added to excess solid sodium carbonate, \({\text{N}}{{\text{a}}_{\text{2}}}{\text{C}}{{\text{O}}_{\text{3}}}{\text{(s)}}\), an acid–base reaction occurs. Bubbles of gas are produced and the solid sodium carbonate decreases in mass. State <strong>one </strong>difference which would be observed if nitric acid, \({\text{HN}}{{\text{O}}_{\text{3}}}{\text{(aq)}}\), was used instead of ammonium chloride.</p>
<p class="p1">(ii) <span class="Apple-converted-space"> </span>Deduce the Lewis structures of the ammonium ion, \({\text{NH}}_4^ + \), and the carbonate ion, \({\text{CO}}_3^{2 - }\).</p>
<p class="p1" style="text-align: center;">Ammonium ion\(\quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \)Carbonate ion</p>
<p class="p1">(iii) <span class="Apple-converted-space"> </span>Predict the shapes of \({\text{NH}}_4^ + \) and \({\text{CO}}_3^{2 - }\).</p>
<p class="p1">\({\text{NH}}_4^ + \):</p>
<p class="p1">\({\text{CO}}_3^{2 - }\):</p>
<div class="marks">[5]</div>
<div class="question_part_label">c.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">(i) <span class="Apple-converted-space"> </span>Sketch and label an enthalpy level diagram for this reaction.</p>
<p class="p1">(ii) <span class="Apple-converted-space"> </span>Deduce whether the reactants or the products are more energetically stable, stating your reasoning.</p>
<p class="p1">(iii) <span class="Apple-converted-space"> </span>Calculate the change in heat energy, in kJ, when \({\text{50.0 c}}{{\text{m}}^{\text{3}}}\) of \({\text{2.50 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}\) sodium hydroxide solution is added to excess nitric acid.</p>
<div class="marks">[6]</div>
<div class="question_part_label">d.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">When 5.35 g ammonium chloride, \({\text{N}}{{\text{H}}_{\text{4}}}{\text{Cl(s)}}\), is added to \({\text{100.0 c}}{{\text{m}}^{\text{3}}}\) of water, the temperature of the water decreases from 19.30 °C to 15.80 °C. Determine the enthalpy change, in \({\text{kJ}}\,{\text{mo}}{{\text{l}}^{ - 1}}\), for the dissolving of ammonium chloride in water.</p>
<div class="marks">[3]</div>
<div class="question_part_label">e.</div>
</div>
<br><hr><br><div class="specification">
<p>When nitrogen gas and hydrogen gas are allowed to react in a closed container, the following equilibrium is established.</p>
<p>\[{{\text{N}}_{\text{2}}}{\text{(g)}} + {\text{3}}{{\text{H}}_{\text{2}}}{\text{(g)}} \rightleftharpoons {\text{2N}}{{\text{H}}_{\text{3}}}{\text{(g)}}\;\;\;\;\;\Delta H = - 92.6{\text{ kJ}}\]</p>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Outline <strong>two </strong>characteristics of a reversible reaction in a state of dynamic equilibrium.</p>
<div class="marks">[2]</div>
<div class="question_part_label">a.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Deduce the equilibrium constant expression, \({K_{\text{c}}}\), for the reaction.</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>Predict, with a reason, how each of the following changes affects the position of equilibrium.</p>
<p> </p>
<p>The volume of the container is increased.</p>
<p> </p>
<p> </p>
<p>Ammonia is removed from the equilibrium mixture.</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>Define the term <em>activation energy</em>, \({E_{\text{a}}}\).</p>
<div class="marks">[1]</div>
<div class="question_part_label">d.i.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Ammonia is manufactured by the Haber process in which iron is used as a catalyst. Explain the effect of a catalyst on the rate of reaction.</p>
<div class="marks">[2]</div>
<div class="question_part_label">d.ii.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Sketch the Maxwell–Boltzmann energy distribution curve for a reaction, labelling both axes and showing the activation energy with and without a catalyst.</p>
<div class="marks">[2]</div>
<div class="question_part_label">d.iii.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Typical conditions used in the Haber process are 500 °C and 200 atm, resulting in approximately 15% yield of ammonia.</p>
<p>(i) Explain why a temperature lower than 500 °C is <strong>not </strong>used.</p>
<p> </p>
<p> </p>
<p> </p>
<p>(ii) Outline why a pressure higher than 200 atm is <strong>not </strong>often used.</p>
<div class="marks">[3]</div>
<div class="question_part_label">e.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Define the term <em>base </em>according to the Lewis theory.</p>
<div class="marks">[1]</div>
<div class="question_part_label">f.i.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Define the term <em>weak base </em>according to the Brønsted-Lowry theory.</p>
<div class="marks">[1]</div>
<div class="question_part_label">f.ii.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Deduce the formulas of conjugate acid-base pairs in the reaction below.</p>
<p>\[{\text{C}}{{\text{H}}_{\text{3}}}{\text{N}}{{\text{H}}_{\text{2}}}{\text{(aq)}} + {{\text{H}}_{\text{2}}}{\text{O(l)}} \rightleftharpoons {\text{C}}{{\text{H}}_{\text{3}}}{\text{NH}}_{\text{3}}^ + {\text{(aq)}} + {\text{O}}{{\text{H}}^ - }{\text{(aq)}}\]</p>
<p><img src="images/Schermafbeelding_2016-08-10_om_07.23.57.png" alt="M15/4/CHEMI/SP2/ENG/TZ2/05.f.iii"></p>
<div class="marks">[2]</div>
<div class="question_part_label">f.iii.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Outline an experiment and its results which could be used to distinguish between a strong base and a weak base.</p>
<div class="marks">[3]</div>
<div class="question_part_label">f.iv.</div>
</div>
<br><hr><br><div class="specification">
<p>Across period 3, elements increase in atomic number, decrease in atomic radius and increase in electronegativity.</p>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Define the term <em>electronegativity</em>.</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>Explain why the atomic radius of elements decreases across the period.</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>State the equations for the reactions of sodium oxide with water and phosphorus(V) oxide with water.</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>Suggest the pH of the solutions formed in part (c) (i).</p>
<div class="marks">[2]</div>
<div class="question_part_label">c.ii.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Describe <strong>three </strong>tests that can be carried out in the laboratory, and the expected results, to distinguish between \({\text{0.10 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}{\text{ HCl(aq)}}\) and \({\text{0.10 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}{\text{ C}}{{\text{H}}_{\text{3}}}{\text{COOH(aq)}}\).</p>
<div class="marks">[3]</div>
<div class="question_part_label">d.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Explain whether BF<sub>3</sub> can act as a Brønsted-Lowry acid, a Lewis acid or both.</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>Describe the bonding and structure of sodium chloride.</p>
<div class="marks">[2]</div>
<div class="question_part_label">f.i.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>State the formula of the compounds formed between the elements below.</p>
<p> </p>
<p>Sodium and sulfur:</p>
<p> </p>
<p>Magnesium and phosphorus:</p>
<div class="marks">[2]</div>
<div class="question_part_label">f.ii.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Covalent bonds form when phosphorus reacts with chlorine to form \({\text{PC}}{{\text{l}}_{\text{3}}}\). Deduce the Lewis (electron dot) structure, the shape and bond angle in \({\text{PC}}{{\text{l}}_{\text{3}}}\) and explain why the molecule is polar.</p>
<p> </p>
<p>Lewis (electron dot) structure:</p>
<p> </p>
<p>Name of shape:</p>
<p> </p>
<p>Bond angle:</p>
<p> </p>
<p>Explanation of polarity of molecule:</p>
<div class="marks">[4]</div>
<div class="question_part_label">g.</div>
</div>
<br><hr><br>