Name Block: Date: Experiment 12C Determination of a Solubility Product Constant

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1 Name Block: Date: Experiment 12C Determination of a Product Constant Objectives 1. to prepare a number of solutions of each Pb 2+ and I - of differing concentrations 2. to mix combinations of the above solutions and note whether a precipitate occurs 3. to obtain an approximate value of K sp for PbI 2 at room temperature 4. to obtain an approximate value of K sp for PbI 2 at temperatures higher than room temperature Materials Please refer to Experiment 12C: Determination of a Product Constant in Essential Experiments for Chemistry, 2005 by D Morrison and D Scodellaro. Hazardous Chemical: o Lead (II) nitrate is very toxic. Do not get any in your mouth and do not swallow any. Avoid getting any on your skin since it can be absorbed. Wash away any spills or splashes with plenty of water. Report any spills to your teacher. Procedure Please refer to Experiment 12C: Determination of a Product Constant in Essential Experiments for Chemistry, 2005 by D Morrison and D Scodellaro. Disposal Instructions o Empty the contents of all test tubes into the designated waste container. Results Table 1: Initial observations of solutions Pb(NO 3 ) 2 KI Page 1 of 5 pages

2 Table 2: Precipitate formation of differing volumes of Pb(NO 3 ) 2 and KI at room temperature and while heated Test tube A B C D E F Vol M Pb(NO 3 ) 2 (ml) Vol. of water added Vol. of M KI (ml) Vol. of water added Precipitate or no precipitate at room temperature Temperature at which precipitate dissolves ( ) Additional observations: Page 2 of 5 pages

3 Questions 1. For each of the test tubes A to F, calculate the [Pb 2+ ] in the final mixed solution. In using the appropriate dilution factor, remember that the final volume in each case is the sum of the volumes of both the lead (II) nitrate and the potassium iodide and the water (ie. 20 ml). 2. Repeat for [I - ] in the final mixed solution in test tubes A to F. 3. Calculate the value of the trial ion product for each of the test tubes A to F (given by [Pb 2+ ][I - ] State the range of values in which your experimental K sp must lie. (This will be between the trial ion product of the last test tube giving a precipitate and the trial ion product of the first test tube not giving a precipitate. Page 3 of 5 pages

4 5. From the results of Step 12 in Table 1, fill in the following table. (Since in each situation the [I - ] was twice the [Pb 2+ ], the solubility of PbI 2 is given simply by the [Pb 2+ ] alone. Test tube D Test tube C Test tube B Test tube A Temperature ( ) K sp (M) 6. What is the trend in the solubility as the temperature is increased? 7. Plot a graph of solubility (moles per litre) against temperature. 8. If you were given a saturated solution of lead (II) iodide and asked to determine the K sp of PbI 2 from it, how would you proceed experimentally? (looking up Ksp on the table doesn t count!) 9. Will lead (II) iodide be more or less soluble in a solution of 0.10 M KI than it will be in pure water? Explain your answer. 10. After doing this experiment, a student finds that the test tubes have a coating of yellow lead (II) iodide on the inside which doesn t wash off easily. On the basis of your experimental results, suggest the best method for removing this coating. Page 4 of 5 pages

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