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3 marksAcid/Base Equilibria

CAPE Chemistry Unit 1 · May/June 2019 · Paper 2 · Question 2(b)(iii)

Determine the pKa of carbonic acid and compare its strength with an aqueous solution of hydrogen sulfide (Ka of hydrogen sulfide = 8.9 x 10^-8).

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  1. 2(a)(i)Using the Bronsted-Lowry theory, differentiate between a 'strong acid' and a 'weak acid'.[2 marks]
  2. 2(a)(ii)Carbonic acid forms a weak acidic solution in water. Write an equation to represent the change when carbonic acid is dissolved in water.[2 marks]
  3. 2(a)(iii)State TWO weak acids other than carbonic acid.[2 marks]
  4. 2(b)(i)Define EACH of the terms pH and pKa.[2 marks]
  5. 2(b)(ii)Calculate the pH of a 0.100 mol dm^-3 aqueous solution of carbonic acid (Ka of carbonic acid = 4.5 x 10^-7 at the experimental temperature).[2 marks]
  6. 2(b)(iv)Sketch a labelled graph to show the pH changes which occur during the titration of 25 cm^3 of 0.10 mol dm^-3 carbonic acid with 0.10 mol dm^-3 of sodium…[3 marks]
  7. 2(c)(i)Define the term 'buffer solution'.[1 mark]
  8. 2(c)(ii)State the components of TWO buffer systems in the blood.[2 marks]
  9. 2(c)(iii)Explain, using an equation, how ONE of the buffer systems in (c)(ii) operates to maintain the pH of blood when acid is added.[2 marks]
  10. 2(d)(i)Write the expression for the solubility product of calcium hydroxide.[1 mark]
  11. 2(d)(ii)Calculate the solubility of calcium hydroxide in g dm^-3 (Ksp Ca(OH)2 = 5.5 x 10^-6 mol^3 dm^-9).[3 marks]
  12. 2(d)(iii)Outline the experimental steps required to determine the solubility product of calcium hydroxide.[5 marks]

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