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</div><h2>HL Paper 1</h2><div class="question">
<p class="p1">Which mixtures act as buffer solutions?</p>
<p class="p1">I. <span class="Apple-converted-space"> </span>\({\text{100 c}}{{\text{m}}^{\text{3}}}{\text{ 0.1 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}\) ethanoic acid and \({\text{100 c}}{{\text{m}}^{\text{3}}}{\text{ 0.1 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}\) sodium ethanoate</p>
<p class="p1">II. <span class="Apple-converted-space"> </span>\({\text{100 c}}{{\text{m}}^{\text{3}}}{\text{ 0.1 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}\) ethanoic acid and \({\text{50 c}}{{\text{m}}^{\text{3}}}{\text{ 0.1 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}\) sodium hydroxide</p>
<p class="p1">III. <span class="Apple-converted-space"> </span>\({\text{100 c}}{{\text{m}}^{\text{3}}}{\text{ 0.1 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}\) ethanoic acid and \({\text{100 c}}{{\text{m}}^{\text{3}}}{\text{ 0.5 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}\) sodium hydroxide</p>
<p class="p1">A. <span class="Apple-converted-space"> </span>I and II only</p>
<p class="p1">B. <span class="Apple-converted-space"> </span>I and III only</p>
<p class="p1">C. <span class="Apple-converted-space"> </span>II and III only</p>
<p class="p1">D. <span class="Apple-converted-space"> </span>I, II and III</p>
</div>
<h2 style="margin-top: 1em">Markscheme</h2>
<div class="question">
<p>A</p>
</div>
<h2 style="margin-top: 1em">Examiners report</h2>
<div class="question">
[N/A]
</div>
<br><hr><br><div class="question">
<p>A buffer solution is formed by mixing equal volumes of \({\text{1.00 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}\) propanoic acid and \({\text{0.500 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}\) potassium propanoate.</p>
<p>What is the concentration, in \({\text{mol}}\,{\text{d}}{{\text{m}}^{ - 3}}\), of \({\text{[}}{{\text{H}}^ + }{\text{(aq)]}}\) in this buffer solution? (\({K_{\text{a}}}\) for propanoic acid is \(1.30 \times {10^{ - 5}}\).)</p>
<p>A. \(2.60 \times {10^{ - 5}}\)</p>
<p>B. \(1.95 \times {10^{ - 5}}\)</p>
<p>C. \(1.30 \times {10^{ - 5}}\)</p>
<p>D. \(0.650 \times {10^{ - 5}}\)</p>
</div>
<h2 style="margin-top: 1em">Markscheme</h2>
<div class="question">
<p>A</p>
</div>
<h2 style="margin-top: 1em">Examiners report</h2>
<div class="question">
<p>This proved to be answered correctly by fewest candidates (37.59%) with many choosing option D, reversing [HA] and \({\text{[}}{{\text{A}}^ - }{\text{]}}\).</p>
</div>
<br><hr><br><div class="question">
<p class="p1">The \({\text{p}}{K_{\text{a}}}\) of ethanoic acid is 4.8 at 298 K. Which combination will produce a buffer solution with a pH of 4.8 at 298 K?</p>
<p class="p1">A. <span class="Apple-converted-space"> </span>\({\text{20.0 c}}{{\text{m}}^{\text{3}}}{\text{ of 1.0 mol}}\,{\text{d}}{{\text{m}}^{ - {\text{3}}}}{\text{ C}}{{\text{H}}_{\text{3}}}{\text{COOH and 10.0 c}}{{\text{m}}^{\text{3}}}{\text{ of 1.0 mol}}\,{\text{d}}{{\text{m}}^{ - {\text{3}}}}{\text{ NaOH}}\)</p>
<p class="p1">B. <span class="Apple-converted-space"> </span>\({\text{20.0 c}}{{\text{m}}^{\text{3}}}{\text{ of 1.0 mol}}\,{\text{d}}{{\text{m}}^{ - {\text{3}}}}{\text{ C}}{{\text{H}}_{\text{3}}}{\text{COOH and 20.0 c}}{{\text{m}}^{\text{3}}}{\text{ of 1.0 mol}}\,{\text{d}}{{\text{m}}^{ - {\text{3}}}}{\text{ NaOH}}\)</p>
<p class="p1">C. <span class="Apple-converted-space"> </span>\({\text{10.0 c}}{{\text{m}}^{\text{3}}}{\text{ of 1.0 mol}}\,{\text{d}}{{\text{m}}^{ - {\text{3}}}}{\text{ C}}{{\text{H}}_{\text{3}}}{\text{COOH and 20.0 c}}{{\text{m}}^{\text{3}}}{\text{ of 1.0 mol}}\,{\text{d}}{{\text{m}}^{ - {\text{3}}}}{\text{ NaOH}}\)</p>
<p class="p1">D. <span class="Apple-converted-space"> </span>\({\text{14.8 c}}{{\text{m}}^{\text{3}}}{\text{ of 1.0 mol}}\,{\text{d}}{{\text{m}}^{ - {\text{3}}}}{\text{ C}}{{\text{H}}_{\text{3}}}{\text{COOH and 10.0 c}}{{\text{m}}^{\text{3}}}{\text{ of 1.0 mol}}\,{\text{d}}{{\text{m}}^{ - {\text{3}}}}{\text{ NaOH}}\)</p>
</div>
<h2 style="margin-top: 1em">Markscheme</h2>
<div class="question">
<p class="p1">A</p>
</div>
<h2 style="margin-top: 1em">Examiners report</h2>
<div class="question">
[N/A]
</div>
<br><hr><br><div class="question">
<p class="p1">Which mixture will form a buffer in aqueous solution?</p>
<p class="p1">A. <span class="Apple-converted-space"> </span>\({\text{0.10 mol N}}{{\text{H}}_{\text{3}}} + {\text{0.20 mol HCl}}\)</p>
<p class="p1">B. <span class="Apple-converted-space"> </span>\({\text{0.10 mol N}}{{\text{H}}_{\text{3}}} + {\text{0.20 mol NaOH}}\)</p>
<p class="p2">C. <span class="Apple-converted-space"> </span>\({\text{0.10 mol NaOH}} + {\text{0.20 mol KCl}}\)</p>
<p class="p1">D. <span class="Apple-converted-space"> </span>\({\text{0.20 mol N}}{{\text{H}}_{\text{3}}} + {\text{0.10 mol HCl}}\)</p>
</div>
<h2 style="margin-top: 1em">Markscheme</h2>
<div class="question">
<p class="p1">D</p>
</div>
<h2 style="margin-top: 1em">Examiners report</h2>
<div class="question">
[N/A]
</div>
<br><hr><br>