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Acids and bases (A-level only)

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Question 51

An aqueous solution of fluoroacetic acid, CH2FCOOH\text{CH}_2\text{FCOOH}CH2​FCOOH, is allowed to reach equilibrium at 298 K according to the equation:

CH2FCOOH(aq)⇌H+(aq)+CH2FCOO−(aq) \text{CH}_2\text{FCOOH(aq)} \rightleftharpoons \text{H}^+\text{(aq)} + \text{CH}_2\text{FCOO}^-\text{(aq)} CH2​FCOOH(aq)⇌H+(aq)+CH2​FCOO−(aq)

At equilibrium, the concentration of undissociated fluoroacetic acid is [CH2FCOOH]=3.20×10−2 mol dm−3[\text{CH}_2\text{FCOOH}] = 3.20 \times 10^{-2}\text{ mol dm}^{-3}[CH2​FCOOH]=3.20×10−2 mol dm−3 and the concentration of fluoroacetate ions is [CH2FCOO−]=8.40×10−3 mol dm−3[\text{CH}_2\text{FCOO}^-] = 8.40 \times 10^{-3}\text{ mol dm}^{-3}[CH2​FCOO−]=8.40×10−3 mol dm−3.

What is the value of the acid dissociation constant, KaK_aKa​, for fluoroacetic acid at 298 K?

A

2.63×10−12.63 \times 10^{-1}2.63×10−1

B

2.26×10−62.26 \times 10^{-6}2.26×10−6

C

2.21×10−32.21 \times 10^{-3}2.21×10−3

D

4.54×1024.54 \times 10^24.54×102

Markscheme

Acids and bases (A-level only) Questions

  1. A Level
  2. /Chemistry
  3. /Acids and bases (A-level only)

77 exam-style questions on AQA A Level Chemistry Acids and bases (A-level only), covering Brønsted–Lowry acid–base equilibria in aqueous solution (A-level only), Definition and determination of pH (A-level only), The ionic product of water, $K_w$ (A-level only), Weak acids and bases $K_a$ for weak acids (A-level only), pH curves, titrations and indicators (A-level only), and Buffer action (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.

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