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3 marksPrinciples of Chemical Equilibrium

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

When a 0.218 mol sample of hydrogen iodide was heated in a flask of volume V dm³, the equilibrium 2HI(g) <=> H2(g) + I2(g) was established at 700 K. The equilibrium mixture contained 0.023 mol of hydrogen.

Calculate the number of moles of iodine and the number of moles of hydrogen iodide in the equilibrium mixture.

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  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)(ii)Write an expression for Kc for the equilibrium 2HI(g) <=> H2(g) + I2(g).[1 mark]
  7. 2(c)(iii)Calculate the value of Kc at 700 K for the equilibrium 2HI(g) <=> H2(g) + I2(g).[2 marks]
  8. 2(c)(iv)Calculate the value of Kc at 700 K for the equilibrium reaction H2(g) + I2(g) <=> 2HI(g).[1 mark]
  9. 2(d)(i)State the meaning of the term 'buffer solution'.[2 marks]
  10. 2(d)(ii)Identify a reagent which could be added to a solution of ammonia in order to form a buffer solution.[1 mark]
  11. 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]
  12. 2(d)(iv)Explain how the molecular structure of amino acids relates to their function as buffers in human blood.[3 marks]
  13. 2(e)(i)Identify TWO relevant pieces of apparatus and/or materials that may have been used by the students to carry out the experiment.[2 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]

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