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1 markAcid/Base Equilibria

CAPE Chemistry Unit 1 · 2007 · Paper 2 · Question 2(a)(i)

Methanoic acid, HCOOH, the irritant found in the sting of an ant, is a weak acid with an acid dissociation constant, Kₐ, of 1.6 x 10⁻⁴ mol dm⁻³. HCOOH(aq) + H₂O(l) ⇌ H₃O⁺(aq) + HCOO⁻(aq).

Explain what is meant by the term 'weak acid'.

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Other parts of this question

  1. 2(a)(ii)Write an expression for the dissociation constant, Kₐ, of methanoic acid.[1 mark]
  2. 2(b)(i)Using Bronsted-Lowry theory, explain what is meant by a strong base.[2 marks]
  3. 2(b)(ii)Calculate the pH of the standard NaOH solution.[2 marks]
  4. 2(b)(iii)The concentration of methanoic acid in Solution Y is found to be 6.0 x 10⁻³ mol dm⁻³. Calculate the pH of Solution Y.[2 marks]
  5. 2(b)(iv)Suggest a suitable indicator for the titration between methanoic acid and sodium hydroxide.[1 mark]
  6. 2(b)(v)Sketch a graph to illustrate the changes in pH that take place during the titration.[4 marks]
  7. 2(c)Ant stings can be treated with baking soda, NaHCO₃. Suggest, with the aid of an equation, how baking soda helps to relieve the effect of the sting.[2 marks]

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