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5 marksAcidic and Basic Character of Organic Compounds

CAPE Chemistry Unit 2 · 2005 · Paper 2 · Question 4(a)

Niacin (nicotinic acid) is a weak acid. A 0.020 mol dm-3 solution has a pH of 3.26 at 298 K.

By reference to the Bronsted-Lowry theory and the molecular structure of niacin, explain the statement, "Niacin is a weak acid".

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Other parts of this question

  1. 4(b)(i)Calculate the concentration of H+ ions in the 0.020 mol dm-3 solution of niacin at 298 K.[3 marks]
  2. 4(b)(ii)Calculate the concentrations of niacin and the conjugate base in solution at 298 K.[3 marks]
  3. 4(b)(iii)Calculate Ka for niacin at 298 K.[3 marks]
  4. 4(c)(i)What changes in the values of pH and Ka for niacin would be expected if the determination is carried out at 320 K? Suggest a reason based on molecular…[3 marks]
  5. 4(c)(ii)Comment on the suitability of using a weak base to determine the concentration of niacin in solution by titration.[3 marks]

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