Chemistry 9701 · AS & A Level · Equilibria

Equilibria — practice question

(a(i))[1]

State what the term partition coefficient means.

(a(ii))[2]

Ammonia dissolves in both water and organic solvents. An aqueous ammonia solution is shaken with the immiscible organic solvent trichloromethane and allowed to reach equilibrium. Samples from each layer are then titrated with dilute hydrochloric acid. A $25.0\,\text{cm}^3$ portion from the trichloromethane layer needs $13.0\,\text{cm}^3$ of $0.100\,\text{mol dm}^{-3}$ HCl to reach the end-point. A $10.0\,\text{cm}^3$ portion from the aqueous layer needs $12.5\,\text{cm}^3$ of $0.100\,\text{mol dm}^{-3}$ HCl to reach the end-point. Calculate the partition coefficient, $K_{\text{partition}}$, of ammonia between trichloromethane and water.

(a(iii))[2]

Butylamine, $\text{C}_4\text{H}_9\text{NH}_2$, is also soluble in both water and organic solvents. Predict how $K_{\text{partition}}$ for butylamine between trichloromethane and water would compare with the value of $K_{\text{partition}}$ from (ii). Give a reason for your answer.

(b(i))[1]

Explain why butylamine shows basic behaviour.

(b(ii))[1]

Write an equation showing butylamine reacting as a base.

(b(iii))[1]

State how the basic strength of butanamide, $\text{C}_3\text{H}_7\text{CONH}_2$, compares with that of butylamine.

(b(iv))[1]

State a reagent that can convert butanamide to butylamine.

Worked solution & mark scheme

This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: Concentration ratio of a solute in two solvents at equilibrium

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