May/June 2026 Paper 42

2026 · 9 questions · 56 parts · 100 marks

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4(a)Dynamic Equilibria Equilibrium ConstantsEasy1 mark

State what is meant by partition coefficient,

K_{p c}

4(b)Dynamic Equilibria Equilibrium ConstantsHard3 marks

Ethanedioic acid, H

_{2}

_{2}

_{4}

, is more soluble in water than in the organic solvent ethoxyethane. 2.70 g of ethanedioic acid is shaken with a mixture of 50 cm

^{3}

of ethoxyethane and 50 cm

^{3}

of water at 298 K and left until there is no further change in concentrations. The ethoxyethane layer requires 16.5 cm

^{3}

of 0.200 mol dm

^{- 3}

NaOH(aq) for complete neutralisation.

H_{2} C_{2} O_{4} + 2 N a O H \to N a_{2} C_{2} O_{4} + 2 H_{2} O

Calculate the partition coefficient,

K_{p c}

, for ethanedioic acid between ethoxyethane and water.

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4(c)Dynamic Equilibria Equilibrium ConstantsMedium2 marks

The formula of ethanedioic acid is HOOCCOOH. The formula of butanedioic acid is HOOCCH

_{2}

_{2}

COOH. Both acids are soluble in ethoxyethane and in water. Suggest how the value of

K_{p c}

of butanedioic acid between ethoxyethane and water compares to the value of

K_{p c}

for ethanedioic acid between ethoxyethane and water. Explain your answer.

Answer

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