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4 marksBuffers and pH

CAPE Chemistry Unit 1 · 2010 · Paper 2 · Question 5(d)

A buffer solution is made by adding 20.5 g of sodium ethanoate (CH3COONa) to 500 cm³ of 1.5 mol dm⁻³ ethanoic acid. (Ka = 1.7 x 10⁻⁵ at 25 °C for ethanoic acid).

Calculate the pH of this buffer solution. (Relative atomic mass: H = 1, C = 12, O = 16, Na = 23)

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Other parts of this question

  1. 5(a)(i)Define EACH of the following terms: pH[2 marks]
  2. 5(a)(ii)Define EACH of the following terms: Buffer solution[2 marks]
  3. 5(b)(i)Write an expression for the acid dissociation constant (Ka) of ethanoic acid.[1 mark]
  4. 5(b)(ii)Calculate the equilibrium concentration of ethanoic acid in a solution that has a pH of 5.[4 marks]
  5. 5(c)(i)State the effect, on the equilibrium position of a buffer solution, of adding small amounts of H+(aq)[1 mark]
  6. 5(c)(ii)State the effect, on the equilibrium position of a buffer solution, of adding small amounts of OH-(aq).[1 mark]

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