Buffer solutionsEdexcel International A Level Chemistry: Mind map

Exam questions on Buffer solutions

1. A technician prepares solutions containing ethanoic acid and sodium ethanoate. The Ka of ethanoic acid is 1.74 × 10⁻⁵ mol dm⁻³, so its pKa is 4.76.
   Explain how a buffer made from ethanoic acid and sodium ethanoate resists a change in pH when a small amount of hydrochloric acid is added.2 marks
2. Human blood is kept at a pH of about 7.4. This is maintained largely by a buffer system based on carbonic acid, H₂CO₃, and hydrogencarbonate ions, HCO₃⁻.
   Explain why it is important that the pH of blood remains almost constant, and how the buffer achieves this.2 marks
3. A technician needs 500 cm³ of a buffer solution of pH 5.00. The final buffer must contain ethanoic acid at a concentration of 0.500 mol dm⁻³, and the conjugate base is supplied by solid sodium ethanoate, CH₃COONa (M = 82.0 g mol⁻¹). The Ka of ethanoic acid is 1.74 × 10⁻⁵ mol dm⁻³.
   Calculate the mass of sodium ethanoate needed.3 marks