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2 marksBuffers and pH

CAPE Chemistry Unit 1 · 2021 · Paper 2 · Question 2(e)(i)

Students are asked to determine the pH of a buffer made by adding measured quantities of ethanoic acid and sodium ethanoate.

Identify TWO relevant pieces of apparatus and/or materials that may have been used by the students to carry out the experiment.

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Other parts of this question

  1. 2(a)(i)Using the data from Experiment 1 in Table 1, calculate a value for the rate constant, k, and state its units.[3 marks]
  2. 2(a)(ii)Complete Table 1 by inserting the missing initial [Q], initial [R] and initial rate for the reaction between Q and R.[4 marks]
  3. 2(a)(iii)The order of the reaction with respect to R is 2. State the meaning of the term 'order of reaction' with respect to R.[1 mark]
  4. 2(a)(iv)Deduce the overall order of the reaction between Q and R.[1 mark]
  5. 2(b)A fixed mass of marble lumps is reacted with dilute hydrochloric acid at a constant temperature. Outline why the rate of the reaction would increase if the…[2 marks]
  6. 2(c)(i)Calculate the number of moles of iodine and the number of moles of hydrogen iodide in the equilibrium mixture.[3 marks]
  7. 2(c)(ii)Write an expression for Kc for the equilibrium 2HI(g) <=> H2(g) + I2(g).[1 mark]
  8. 2(c)(iii)Calculate the value of Kc at 700 K for the equilibrium 2HI(g) <=> H2(g) + I2(g).[2 marks]
  9. 2(c)(iv)Calculate the value of Kc at 700 K for the equilibrium reaction H2(g) + I2(g) <=> 2HI(g).[1 mark]
  10. 2(d)(i)State the meaning of the term 'buffer solution'.[2 marks]
  11. 2(d)(ii)Identify a reagent which could be added to a solution of ammonia in order to form a buffer solution.[1 mark]
  12. 2(d)(iii)Consider the equilibrium HA(aq) + H2O(l) <=> H3O+(aq) + A-(aq). Explain the effect on the buffer solution if the concentrations of hydrogen ions [H+] and…[2 marks]
  13. 2(d)(iv)Explain how the molecular structure of amino acids relates to their function as buffers in human blood.[3 marks]
  14. 2(e)(ii)Identify TWO relevant experimental steps that may have been taken by the students to determine the pH of the buffer.[2 marks]

More practice: the rest of this paper · more Buffers and pH questions · all CAPE Chemistry Unit 1 past papers