Chemistry 9701 · AS & A Level · Equilibria

Equilibria — practice question

(a(i))[2]

Using $\text{HZ}$ to denote a Brønsted-Lowry acid, write equations showing these substances acting as Brønsted-Lowry bases: $\text{NH}_3$ and $\text{CH}_3\text{OH}$.

(a(ii))[2]

Using $\text{B}^-$ to denote a Brønsted-Lowry base, write equations showing these substances acting as Brønsted-Lowry acids: $\text{NH}_3$ and $\text{CH}_3\text{OH}$.

(b(i))[1]

State briefly what the term reversible reaction means.

(b(ii))[1]

State briefly what the term dynamic equilibrium means.

(c(i))[2]

Explain the meaning of the term buffer solution.

(c(ii))[2]

Explain how a buffer solution works by means of a reversible reaction involving a Brønsted-Lowry acid such as $\text{HZ}$ and a Brønsted-Lowry base such as $\text{Z}^-$.

(d(i))[2]

Propanoic acid, $\text{CH}_3\text{CH}_2\text{CO}_2\text{H}$, is a weak acid and has $K_a = 1.34 \times 10^{-5}\ \text{mol dm}^{-3}$. Calculate the pH of a $0.500\ \text{mol dm}^{-3}$ solution of propanoic acid.

(d(ii))[1]

Buffer solution F was made by adding $0.0300\ \text{mol}$ of sodium hydroxide to $100\ \text{cm}^3$ of a $0.500\ \text{mol dm}^{-3}$ propanoic acid solution. Write an equation for the reaction between sodium hydroxide and propanoic acid.

(d(iii))[2]

Calculate the concentrations of propanoic acid and sodium propanoate in buffer solution F.

(d(iv))[1]

Calculate the pH of buffer solution F.

(e)[2]

Phenyl propanoate cannot be produced directly from propanoic acid and phenol. Suggest the identities of the intermediate $\text{G}$, the reagent $\text{H}$ and the by-product $\text{J}$ in the reaction scheme shown.

Worked solution & mark scheme

This 18-mark question has a full step-by-step worked solution and mark scheme. One marking point: Equation: $\text{NH}_3 + \text{HZ} \rightarrow \text{NH}_4^+ + \text{Z}^-$

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