DP Chemistry (first assessment 2025)
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Reactivity 3.1—Proton transfer reactions

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Reactivity 3.1.1—Brønsted–Lowry acid is a proton donor and a Brønsted–Lowry base is a proton acceptor. Deduce the Br.nsted–Lowry acid and base in a reaction.

Reactivity 3.1.2—A pair of species differing by a single proton is called a conjugate acid–base pair. Deduce the formula of the conjugate acid or base of any Br.nsted–Lowry base or acid.

Reactivity 3.1.3—Some species can act as both Brønsted–Lowry acids and bases. Interpret and formulate equations to show acid–base reactions of these species.

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Reactivity 3.1.4—The pH scale can be used to describe the [H+] of a solution: pH = –log10[H+]; [H+] = 10–pH. Perform calculations involving the logarithmic relationship between pH and [H+].

Reactivity 3.1.5—The ion product constant of water, Kw, shows an inverse relationship between [H+] and [OH–]. Kw = [H+] [OH–]. Recognize solutions as acidic, neutral and basic from the relative values of [H+] and [OH–].

Reactivity 3.1.6—Strong and weak acids and bases differ in the extent of ionization. Recognize that acid–base equilibria lie in the direction of the weaker conjugate. and are strong acids, and group 1 hydroxides are strong bases.

Reactivity 3.1.7—Acids react with bases in neutralization reactions. Formulate equations for the reactions between acids and metal oxides, metal hydroxides, hydrogencarbonates and carbonates.

Reactivity 3.1.8—pH curves for neutralization reactions involving strong acids and bases have characteristic shapes and features. Sketch and interpret the general shape of the pH curve.

Reactivity 3.1.9—The pOH scale describes the [OH–] of a solution. pOH = –log10[OH–]; [OH–] = 10–pOH. Interconvert [H+], [OH–], pH and pOH values.

Reactivity 3.1.10—The strengths of weak acids and bases are described by their Ka, Kb, pKa or pKb values. Interpret the relative strengths of acids and bases from these data.

Reactivity 3.1.11—For a conjugate acid–base pair, the relationship Ka Å~ Kb = Kw can be derived from the expressions for Ka and Kb. Solve problems involving these values.

Reactivity 3.1.12—The pH of a salt solution depends on the relative strengths of the parent acid and base. Construct equations for the hydrolysis of ions in a salt, and predict the effect of each ion on the pH of the salt solution.

Reactivity 3.1.13—pH curves of different combinations of strong and weak monoprotic acids and bases have characteristic shapes and features. Interpret the general shapes of pH curves for all four combinations of strong and weak acids and bases.

Reactivity 3.1.14—Acid–base indicators are weak acids, where the components of the conjugate acid–base pair have different colours. The pH of the end point of an indicator, where it changes colour, approximately corresponds to its pKa value. Construct equilibria expressions to show why the colour of an indicator changes with pH.

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Reactivity 3.1.15—An appropriate indicator for a titration has an end point range that coincides with the pH at the equivalence point. Identify an appropriate indicator for a titration from the identity of the salt and the pH range of the indicator.

Reactivity 3.1.16—A buffer solution is one that resists change in pH on the addition of small amounts of acid or alkali. Describe the composition of acidic and basic buffers and explain their actions.

Reactivity 3.1.17—The pH of a buffer solution depends on both: • the pKa or pKb of its acid or base • the ratio of the concentration of acid or base to the concentration of the conjugate base or acid. Solve problems involving the composition and pH of a buffer solution, using the equilibrium constant.