CAIE A-Level Chemistry A2 25.1.4 H Aq and Ph Values Questions

Practise ranking pH values by acid strength, concentration and dissociation in aqueous solutions.

Exam points

relate lower pH to higher hydrogen-ion concentration and compare strong and weak acids at stated concentrations
account for complete or partial acid dissociation and the number of protons released when ranking pH values

[Maximum number: 3]

(a)

The $K_{a}$ of propanoic acid, $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOH}$ , is $1.35 \times 10^{-5} \mathrm{moldm}^{-3}$ at 298 K.

Solution C is a solution of $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOH}$ with a pH of 3.60 at 298 K.

[ 3 ]

(i)

Calculate the concentration of $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOH}$ in solution C.

\left[\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOH}\right]=\ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots . . . \mathrm{mol} \mathrm{dm}^{-3}

[2]

[ 2 ]

M1: $\left[\mathrm{H}^{+}\right]=2.51 \times 10^{-4}$

M2: $\left[\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOH}\right]=4.67 \times 10^{-3}$

(ii)

Calculate the concentration of a solution of hydrochloric acid with the same pH as solution C.

\text{concentration}=..............................\ \mathrm{mol\ dm}^{-3}

[ 1 ]

$[\mathrm{HCl}]=2.51 \times 10^{-4}$

All question bank results loaded

CAIE A-Level Chemistry A2 25.1.4 H Aq and Ph Values Questions question 1

Question (a)

Question (i)

Question (ii)