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5 marksMixtures and Separations

CSEC Chemistry · May/June 2006 · Paper 2 · Question 1(a)(i)b)

A procedure is used to determine the solubility of substance X in water at various temperatures. In Experiment 1, 2g of X is added to 4 cm³ water in a boiling tube. The tube is heated with stirring until all solid X dissolves. The solution is then cooled, and the temperature at which crystals of X first reappear is noted. Experiments 2 to 5 use 2g of X with different volumes of water, and the temperatures at which crystals reappear are shown in Figure 1.

Complete Table 1 by filling in the corresponding solubilities of X (g/100 g water). Use the following equation to calculate the solubility of X at each temperature: Solubility of X (g/100 g water) = (mass of X / mass of water) × 100 (Equation 1). Assume 1 cm³ water = 1 g.

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Other parts of this question

  1. 1(a)(i)a)Complete Table 1 by filling in the temperatures at which crystals of X reappear in EACH experiment using the information in Figure 1.[5 marks]
  2. 1(a)(ii)Using the graph paper provided on page 4, plot a graph of solubility of X (g/100 g water) against temperature in °C.[4 marks]
  3. 1(a)(iii)What deduction about the solubility of X can be made from the graph drawn in Figure 2?[2 marks]
  4. 1(a)(iv)Using Equation 1 and the graph drawn in Figure 2, calculate the volume of water which is required to just dissolve 2 g of X at 60 °C.[3 marks]
  5. 1(a)(v)Based on the graph in Figure 2, calculate the mass of X which would be deposited when 100 g of a solution of X at 60 °C is cooled to 40 °C.[1 mark]
  6. 1(b)(i)Complete Table 2 for the test: To solid Q, add water, stir, filter and then divide the filtrate into four portions. Retain and dry the residue for test (vi)…[2 marks]
  7. 1(b)(ii)Complete Table 2 for the test: To the first portion of the filtrate from (i) above, add aqueous NaOH until in excess. The observations are: White precipitate…[2 marks]
  8. 1(b)(iii)Complete Table 2 for the test: To the second portion of the filtrate from (i) above, add aqueous KI. The observation is: Yellow precipitate formed. Provide the…[2 marks]
  9. 1(b)(iv)Complete Table 2 for the test: To the third portion of the filtrate from (i) above, add aqueous AgNO₃, followed by aqueous NH₃. The observation is: No…[1 mark]
  10. 1(b)(v)Complete Table 2 for the test: To the fourth portion of the filtrate from (i) above, add aqueous AgNO₃, followed by aqueous NH₃. Provide the ionic equation…[2 marks]
  11. 1(b)(vi)Complete Table 2 for the test: To the dried residue from (i) above, add dilute HNO₃, warm, filter and then divide the filtrate into two portions. The…[2 marks]
  12. 1(b)(vii)Complete Table 2 for the test: To the first portion of the filtrate from (vi) above, add aqueous NaOH until in excess. The inference is: Cu²⁺ ions present.…[2 marks]
  13. 1(b)(viii)Complete Table 2 for the test: To the second portion of the filtrate from (vi) above, add aqueous NH₃ until in excess. The inference is: Cu²⁺ ions present.[2 marks]

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