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CAIE IGCSE Chemistry Hydrogen and Hydroxide Ions in Solution

CAIE IGCSE Chemistry Hydrogen and Hydroxide Ions in Solution
Cambridge IGCSE Chemistry 0620 syllabus for exams in 2026, 2027 and 20282026–2028

Practise identifying hydrogen ions as responsible for acidity and hydroxide ions as responsible for alkalinity in aqueous solutions.

How this is tested

  • identify hydrogen ions, H⁺, as the species responsible for acidity in aqueous solution
  • identify hydroxide ions, OH⁻, as the species responsible for alkalinity in aqueous solution

Question 4(f)(ii)

[Maximum number: 1]

A carboxylic acid reacts with an alcohol to produce an ester and water.
Under certain conditions, this reaction can be reversed so an ester reacts with water to produce a carboxylic acid X and an alcohol Y.

The reaction reaches an equilibrium.

CH3CH2COOCH3+H2O⇌X+Y\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOCH}_{3}+\mathrm{H}_{2} \mathrm{O} \rightleftharpoons \mathbf{X}+\mathbf{Y}

The forward reaction is endothermic.

At the beginning of the reaction between the ester and water, no carboxylic acid is present in the reaction mixture.

Identify the ion that causes the change in pH .