Topic 6.1: Proton Transfer Reactions Questions

Hydrogensulfate, HSO₄⁻, is amphiprotic.

Write an equation to show HSO₄⁻ acting as a Brønsted–Lowry base in water, and identify its conjugate acid. [2]

Hydrofluoric acid, HF, has K_a = 5.6 × 10⁻⁴ mol dm⁻³ at 298 K.

(a) Calculate the pK_a of HF.

(b) Calculate K_b and pK_b for the fluoride ion, F⁻, its conjugate base. [3]

For the equilibrium CH₃COOH + H₂O ⇌ CH₃COO⁻ + H₃O⁺, identify the two conjugate acid–base pairs and state which species is the Brønsted–Lowry acid on the left-hand side. [2]

Write a balanced equation for the reaction of zinc carbonate, ZnCO₃, with dilute nitric acid, HNO₃. [2]

A sample of rainwater is found to have a hydrogen-ion concentration of 2.0 × 10⁻⁵ mol dm⁻³.

Calculate its pH.

Dilute sulfuric acid is added to solid copper(II) oxide, CuO, and the mixture warms and turns blue.

(a) Name the type of reaction and the salt formed.

(b) Write a balanced equation for the reaction. [3]

Ethylamine, C₂H₅NH₂, is a weak base.

A student titrates 25.0 cm³ of 0.100 mol dm⁻³ hydrochloric acid with 0.100 mol dm⁻³ ethylamine.

(a) State, with a reason, whether the pH at the equivalence point is greater than, equal to or less than 7.

(b) Choosing from methyl orange (range 3.1–4.4) and phenolphthalein (range 8.3–10.0), identify the more suitable indicator and explain your choice. [4]

Solutions of hydrochloric acid (HCl) and propanoic acid (CH₃CH₂COOH) each have a concentration of 0.10 mol dm⁻³.

Explain why the propanoic acid solution has a higher pH, and state one other experimental observation that would confirm it is the weaker acid. [3]

Lactic acid, CH₃CH(OH)COOH, has K_a = 1.4 × 10⁻⁴ mol dm⁻³ at 298 K.

Calculate the pH of a 0.0080 mol dm⁻³ solution of lactic acid, stating the assumptions you make. [3]

A buffer solution is prepared by mixing 50.0 cm³ of 0.40 mol dm⁻³ methanoic acid, HCOOH (K_a = 1.8 × 10⁻⁴ mol dm⁻³), with 50.0 cm³ of 0.10 mol dm⁻³ sodium methanoate, HCOONa.

Calculate the pH of the buffer. [3]