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2 marksAcid/Base Equilibria

CAPE Chemistry Unit 1 · 2008 · Paper 2 · Question 5(a)(i)

This section covers kinetics and equilibria, specifically focusing on buffer solutions. A buffer solution is prepared using 0.14 mol dm⁻³ lactic acid (HC₃H₅O₃) and 0.12 mol dm⁻³ sodium lactate (NaC₃H₅O₃). The acid dissociation constant (Kₐ) for lactic acid is 1.4 x 10⁻⁴. The equilibrium reaction for lactic acid is given: HC₃H₅O₃(aq) + H₂O(l) ⇌ H₃O⁺(aq) + C₃H₅O₃⁻(aq).

With reference to the Bronsted-Lowry theory, explain EACH of the following: Weak acid

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  1. 5(a)(ii)With reference to the Bronsted-Lowry theory, explain EACH of the following: Strong acid[1 mark]
  2. 5(b)Describe the significance of pH (- log [H⁺]) and Kₐ (acid dissociation constant) values.[2 marks]
  3. 5(c)Calculate the pH of the HC₃H₅O₃ / C₃H₅O₃⁻ buffer solution.[4 marks]
  4. 5(d)With the aid of balanced equations, explain how the HC₃H₅O₃ / C₃H₅O₃⁻ buffer works in maintaining its pH.[6 marks]
  5. 5(e)When preparing a buffer solution of a specific pH, state ONE consideration to be taken into account in selecting a suitable weak acid.[1 mark]

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