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7 marksQualitative Analysis

CSEC Chemistry · January 2005 · Paper 2 · Question 1(b)(i)

A student carries out tests on Substance Z, with observations recorded in Table 1. The task is to complete Table 1 with inferences and equations.

Heat a small sample of solid Z gently in a dry test tube. Observation: Pungent gas evolves which turns damp red litmus blue. Inference: (equation required).

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Other parts of this question

  1. 1(a)(i)From the results shown in Figure 1 construct a table to show experiment number, volume of acid added from the burette, volume of water added to the acid, and…[4 marks]
  2. 1(a)(ii)Using the graph paper on page 4, plot a graph of time taken for the magnesium ribbon to disappear against volume of acid added from the burette.[4 marks]
  3. 1(a)(iii)Explain the shape of the graph.[1 mark]
  4. 1(a)(iv)Using the data from the graph determine the time it would take for 25 cm³ of the acid to react with the magnesium ribbon.[1 mark]
  5. 1(a)(v)Write a balanced equation for the reaction of magnesium with hydrochloric acid.[2 marks]
  6. 1(a)(vi)a)Calculate the number of moles of Mg in 0.12 g (Relative Atomic Mass of Mg = 24).[1 mark]
  7. 1(a)(vi)b)The volume of hydrogen gas produced at r.t.p. when all the magnesium ribbon reacts with the acid (1 mole of gas at r.t.p. occupies 24 dm³).[2 marks]
  8. 1(a)(vii)Explain why it is necessary, for each experiment, to make up the volume of acid to 50 cm³ by adding water.[1 mark]
  9. 1(b)(ii)Add approximately 2 cm³ of aqueous sodium hydroxide to a sample of solid Z and warm. Observation: A gas evolves which forms dense white fumes with hydrogen…[7 marks]
  10. 1(b)(iii)Dissolve a spatula full of solid Z in approximately 10 cm³ of deionized water. Divide the resulting mixture into 3 portions for tests iv - vi. Observation: A…[7 marks]
  11. 1(b)(iv)To one portion of solution Z from (iii) above, add aqueous sodium hydroxide dropwise until in excess. Observation: A green gelatinous precipitate forms. The…[7 marks]
  12. 1(b)(v)To another portion of solution Z from (iii) above, add dilute nitric acid followed by aqueous silver nitrate solution. Observation: No visible reaction seen.…[7 marks]
  13. 1(b)(vi)To another portion of solution Z from (iii) above, add barium nitrate followed by dilute nitric acid. Observation: A white precipitate insoluble in dilute acid…[7 marks]
  14. 1(c)(i)Write up the Aim.[1 mark]
  15. 1(c)(ii)Write up the Method or procedure.[2 marks]
  16. 1(c)(iii)Write up the Discussion of results: Data to be collected.[1 mark]
  17. 1(c)(iii) continuedWrite up the Discussion of results: Steps for doing calculations.[2 marks]
  18. 1(c)(iii) continuedWrite up the Discussion of results as it relates to aim.[1 mark]

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