IB DP Chemistry D.4 pH regulation of the stomach HL Paper 1

Marks available1
Reference code10N.1.hl.TZ0.26

Question

Which mixtures act as buffer solutions?

I.     \({\text{100 c}}{{\text{m}}^{\text{3}}}{\text{ 0.1 mol}}\,{\text{d}}{{\text{m}}^{ – 3}}\) ethanoic acid and \({\text{100 c}}{{\text{m}}^{\text{3}}}{\text{ 0.1 mol}}\,{\text{d}}{{\text{m}}^{ – 3}}\) sodium ethanoate

II.     \({\text{100 c}}{{\text{m}}^{\text{3}}}{\text{ 0.1 mol}}\,{\text{d}}{{\text{m}}^{ – 3}}\) ethanoic acid and \({\text{50 c}}{{\text{m}}^{\text{3}}}{\text{ 0.1 mol}}\,{\text{d}}{{\text{m}}^{ – 3}}\) sodium hydroxide

III.     \({\text{100 c}}{{\text{m}}^{\text{3}}}{\text{ 0.1 mol}}\,{\text{d}}{{\text{m}}^{ – 3}}\) ethanoic acid and \({\text{100 c}}{{\text{m}}^{\text{3}}}{\text{ 0.5 mol}}\,{\text{d}}{{\text{m}}^{ – 3}}\) sodium hydroxide

A.     I and II only

B.     I and III only

C.     II and III only

D.     I, II and III

Markscheme

A

Examiners report

[N/A]
Marks available1
Reference code14N.1.hl.TZ0.28

Question

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.

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 \(1.30 \times {10^{ – 5}}\).)

A.     \(2.60 \times {10^{ – 5}}\)

B.     \(1.95 \times {10^{ – 5}}\)

C.     \(1.30 \times {10^{ – 5}}\)

D.     \(0.650 \times {10^{ – 5}}\)

Markscheme

A

Examiners report

This proved to be answered correctly by fewest candidates (37.59%) with many choosing option D, reversing [HA] and \({\text{[}}{{\text{A}}^ – }{\text{]}}\).

Marks available1
Reference code15M.1.hl.TZ1.29

Question

Which mixture will form a buffer in aqueous solution?

A.     \({\text{0.10 mol N}}{{\text{H}}_{\text{3}}} + {\text{0.20 mol HCl}}\)

B.     \({\text{0.10 mol N}}{{\text{H}}_{\text{3}}} + {\text{0.20 mol NaOH}}\)

C.     \({\text{0.10 mol NaOH}} + {\text{0.20 mol KCl}}\)

D.     \({\text{0.20 mol N}}{{\text{H}}_{\text{3}}} + {\text{0.10 mol HCl}}\)

Markscheme

D

Examiners report

[N/A]
Marks available1
Reference code15M.1.hl.TZ2.27

Question

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?

A.     \({\text{20.0 c}}{{\text{m}}^{\text{3}}}{\text{ of 1.0 mol}}\,{\text{d}}{{\text{m}}^{ – {\text{3}}}}{\text{ C}}{{\text{H}}_{\text{3}}}{\text{COOH and 10.0 c}}{{\text{m}}^{\text{3}}}{\text{ of 1.0 mol}}\,{\text{d}}{{\text{m}}^{ – {\text{3}}}}{\text{ NaOH}}\)

B.     \({\text{20.0 c}}{{\text{m}}^{\text{3}}}{\text{ of 1.0 mol}}\,{\text{d}}{{\text{m}}^{ – {\text{3}}}}{\text{ C}}{{\text{H}}_{\text{3}}}{\text{COOH and 20.0 c}}{{\text{m}}^{\text{3}}}{\text{ of 1.0 mol}}\,{\text{d}}{{\text{m}}^{ – {\text{3}}}}{\text{ NaOH}}\)

C.     \({\text{10.0 c}}{{\text{m}}^{\text{3}}}{\text{ of 1.0 mol}}\,{\text{d}}{{\text{m}}^{ – {\text{3}}}}{\text{ C}}{{\text{H}}_{\text{3}}}{\text{COOH and 20.0 c}}{{\text{m}}^{\text{3}}}{\text{ of 1.0 mol}}\,{\text{d}}{{\text{m}}^{ – {\text{3}}}}{\text{ NaOH}}\)

D.     \({\text{14.8 c}}{{\text{m}}^{\text{3}}}{\text{ of 1.0 mol}}\,{\text{d}}{{\text{m}}^{ – {\text{3}}}}{\text{ C}}{{\text{H}}_{\text{3}}}{\text{COOH and 10.0 c}}{{\text{m}}^{\text{3}}}{\text{ of 1.0 mol}}\,{\text{d}}{{\text{m}}^{ – {\text{3}}}}{\text{ NaOH}}\)

Markscheme

A

Examiners report

[N/A]
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