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1 markMixtures and Separations

CSEC Chemistry · May/June 2013 · Paper 2 · Question 1(a)(iii)

Peter designed an experiment to investigate the solubility of potassium iodide (KI) at varying temperatures. The procedure involved measuring 100 cm³ of distilled water, weighing the beaker with water, adding solid potassium iodide until no more dissolved while maintaining temperature, and then weighing the beaker with the salt solution. This was repeated at 20 °C, 40 °C, 60 °C, and 80 °C. Table 1 provides the mass of the beaker with water and the mass of the beaker with salt solution at these temperatures.

From the graph, determine the solubility (in grams per 100 cm³) of potassium iodide at 70 °C.

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Other parts of this question

  1. 1(a)(i)For EACH temperature in Table 1, calculate the mass of potassium iodide that was dissolved in the beaker of water, and record the value in the space provided.[2 marks]
  2. 1(a)(ii)On Figure 1, plot mass of salt dissolved (solubility) against temperature, and draw a straight line through the points.[3 marks]
  3. 1(a)(iv)100 cm³ of distilled water is saturated with potassium iodide at 70 °C. Calculate the mass of potassium iodide that will be precipitated out from solution, if…[2 marks]
  4. 1(a)(v)Calculate the concentration (mol dm⁻³) of a saturated solution of potassium iodide at 30 °C. (RAM: K = 39, I = 127).[3 marks]
  5. 1(b)Explain why the statement above is true.[4 marks]
  6. 1(c)(i)A suggested list of apparatus and chemicals which you will use in obtaining the pure solid sample of EITHER of the two salts.[1 mark]
  7. 1(c)(ii)An outline of the steps for the procedure to be used.[3 marks]
  8. 1(c)(iii)List the MAIN observations that will be expected at EACH stage of the experiment.[2 marks]
  9. 1(d)Complete the table by inserting the appropriate inferences.[4 marks]

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