Chemistry 9701 · AS & A Level · Equilibria

Equilibria — practice question

(a(i))[2]

Using the symbol $\text{HZ}$ to stand for a Brønsted-Lowry acid, write equations to show $\text{NH}_3 +$ and $\text{CH}_3\text{OH} +$ acting as Brønsted-Lowry bases.

(a(ii))[2]

Using the symbol $\text{B}^-$ to stand for a Brønsted-Lowry base, write equations to show $\text{NH}_3 +$ and $\text{CH}_3\text{OH} +$ acting as Brønsted-Lowry acids.

(b(i))[1]

State briefly what is meant by a reaction that is reversible.

(b(ii))[1]

State briefly what is meant by dynamic equilibrium in a reaction mixture.

(c(i))[2]

Explain what the term buffer solution means.

(c(ii))[2]

Explain how the action of a buffer solution depends on 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 with $K_a = 1.34 \times 10^{-5}\,\text{mol dm}^{-3}$. Calculate the $\text{pH}$ of a $0.500\,\text{mol dm}^{-3}$ solution of propanoic acid.

(d(ii))[1]

Write an equation for the reaction of sodium hydroxide with propanoic acid.

(d(iii))[2]

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

(d(iv))[1]

Calculate the $\text{pH}$ of buffer solution $F$.

(e)[2]

Phenyl propanoate cannot be prepared directly from propanoic acid and phenol. In the reaction scheme shown, identify the intermediate $G$, the reagent $H$ and the by-product $J$.

Worked solution & mark scheme

This 18-mark question has a full step-by-step worked solution and mark scheme. One marking point: \mathrm{NH_3 + HZ \rightarrow NH_4^+ + Z^-}

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