The solubility product, Ksp, of a sparingly soluble salt can be determined by measuring the cell potential of a cell known as a concentration cell. One of the half-cells uses a saturated solution of the salt as the electrolyte. The Ksp of silver chloride, AgCl, can be measured using the apparatus shown. [Figure X.X] The silver electrodes of the two half-cells were connected via a voltmeter, reading to three decimal places. This measured the cell potential of the concentration cell. The half-cells were kept at a temperature of 40 °C. Under these conditions, the relationship between cell potential, Ecell, and [Ag⁺(aq)] is 16.1Ecell = log Csat - log [Ag⁺(aq)] Csat is the concentration of the saturated solution of silver chloride

1. (a)(i)The solutions in the half-cells need to be kept at 40 °C. Explain how you would do this.[1]
2. (a)(ii)If the temperature was maintained at 40°C, over time the reading on the voltmeter would change. Suggest one reason why.[1]
3. (b)Complete the fourth and fifth columns of the table. Give each answer to two decimal places. experiment [Ag⁺(aq)] /mol dm⁻³ Ecell/V -log [Ag⁺(aq)] 16.1Ecell/V 1 0.00100 -0.097 2 0.00500 -0.140 3 0.0100 -0.159 4 0.0250 -0.171 5 0.0500 -0.202 6 0.100 -0.221 7 0.200 -0.239 8 0.500 -0.264 9 1.50 -0.294 [2]
4. (c)(i)On the grid on page 9, plot a graph of 16.1Ecell against -log [Ag⁺(aq)]. Draw a line of best fit.[2]
5. (c)(ii)Circle the single most anomalous point on the graph. The temperature of the half-cells was maintained at 40°C. Suggest what error in the experimental set-up may have caused the anomaly.[2]
6. (c)(iii)Use your graph and the equation to determine a value for log Csat. 16.1Ecell = log Csat - log [Ag⁺(aq)] log Csat = .................................[1]
7. (d)(i)For experiment 6, calculate the volume of 2.0 mol dm⁻³ Ag⁺(aq) needed to prepare exactly 250.0 cm³ of Ag⁺(aq) in a 250.0 cm³ volumetric flask.[1]
8. (d)(ii)Name a suitable piece of apparatus which could be used to measure the volume calculated in (i).[1]
9. (e)(i)The relationship between the solubility product, Ksp, and the concentration of the saturated solution of silver chloride, Csat, is shown. Ksp = Csat² Use this equation and your answer to (c)(iii) to calculate a value for Ksp. Give your answer to three significant figures. (If you have no answer for (c)(iii), use a value of –4.20 but this is not the true value.) Ksp = .................................[2]
10. (e)(ii)The solubility of AgCl increases with temperature. Using the axes below, sketch a graph to show how the Ksp of AgCl varies with temperature. Label both axes. [Figure X.X][1]
11. (f)The salt bridge in a concentration cell commonly contains a solution of one of the following compounds. potassium chloride potassium nitrate sodium chloride Identify which, if any, of these compounds would not be suitable for use in the salt bridge in this experiment. Explain your answer.[2]

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