The graph represents the titration of 25.00 cm³ of 0.100 mol dm⁻³ aqueous ethanoic acid with 0.100 mol dm⁻³ aqueous sodium hydroxide.

Deduce the major species, other than water and sodium ions, present at points A and B during the titration.

Calculate the pH of 0.100 mol dm⁻³ aqueous ethanoic acid.

K_a = 1.74 × 10⁻⁵

Outline, using an equation, why sodium ethanoate is basic.

Predict whether the pH of an aqueous solution of ammonium chloride will be greater than, equal to or less than 7 at 298 K.

Formulate the equation for the reaction of nitrogen dioxide, NO₂, with water to form two acids.

Formulate the equation for the reaction of one of the acids produced in (e)(i) with calcium carbonate.

A: CH₃COOH/ethanoic/acetic acid AND CH₃COO^–/ethanoate/acetate ions

B: CH₃COO^–/ethanoate/acetate ions

Penalize “sodium ethanoate/acetate” instead of “ethanoate/acetate ions” only once.

[2 marks]

$K_{\text{a}}=1.74\times {10}^{-5}=\frac{{\text{[}{\text{H}}^{+}\text{]}}^2}{0.10}$

OR

[H⁺] = 1.32 × 10^–3 «mol dm^–3»

«pH =» 2.88

Accept [2] for correct final answer.

[2 marks]

«forms weak acid and strong base, thus basic»

CH₃COO^–(aq) + H₂O(l) $\rightleftharpoons$ CH₃COOH(aq) + OH^–(aq)

Accept → for $\rightleftharpoons$.

[1 mark]

less than 7

[1 mark]

2NO₂(g) + H₂O(l) → HNO₂(aq) + HNO₃(aq)

[1 mark]

2HNO₂(aq) + CaCO₃(s) → Ca(NO₂)₂(aq) + CO₂(g) + H₂O(l)

OR

2HNO₃(aq) + CaCO₃(s) → Ca(NO₃)₂(aq) + CO₂(g) + H₂O(l)

[1 mark]