Chemistry 9701 · AS & A Level · Equilibria

Equilibria — practice question

(a(i))[2]

State the mathematical expressions for pH and $K_w$.

(a(ii))[1]

Calculate the pH for $0.027\,\text{mol dm}^{-3}$ $\text{NaOH}$(aq).

(b)[1]

For chloric(I) acid, $\text{HClO}_2$, the $K_a$ value is $3.72 \times 10^{-8}\,\text{mol dm}^{-3}$. Calculate the pH of $0.010\,\text{mol dm}^{-3}$ $\text{HClO}_2$(aq).

(c(i))[1]

When water and octan-1-ol are mixed, they separate into two layers. Ethanamide is more soluble in water than it is in octan-1-ol. After $1.00\,\text{g}$ of ethanamide is added to $50.0\,\text{cm}^3$ of water and the mixture is then shaken with $50.0\,\text{cm}^3$ of octan-1-ol, it is found at equilibrium that the water layer contains $0.935\,\text{g}$ of ethanamide. Calculate the partition coefficient, $K_{pc}$, for ethanamide in water and octan-1-ol.

(c(ii))[2]

The $50.0\,\text{cm}^3$ of water containing $0.935\,\text{g}$ of ethanamide is then shaken with $100.0\,\text{cm}^3$ of pure octan-1-ol under the same conditions. Calculate the mass of ethanamide that is dissolved in the $100.0\,\text{cm}^3$ of octan-1-ol at equilibrium.

Worked solution & mark scheme

This 7-mark question has a full step-by-step worked solution and mark scheme. One marking point: pH is defined by $pH = -\log[H^+]$.

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