A liquid threat in the pipeline - Lead in tap water can harm children
1 a) In this article, it is implied that lead metal is present in the tap water. In fact the lead dissolves to form lead compounds in the water. Soft water is often slightly acidic. Which common acids might react with lead to form a soluble compound? (Hint: Look up the solubility of salts such as lead sulphate and lead nitrate in a data book.) Would the acids forming these salts be present in tap water? b) Use a list of redox potentials in a data book to suggest possible half-cells which might oxidise Pb (s) to Pb ++ (aq).
2 In one house, the test for lead recorded only 5 microgrammes per litre. Calculate the molarity of Pb ++ (aq) in the water (Pb = 207).
3 Given the extremely low molarity of the lead in tap water, do you think that simple tests for lead such as titration and precipitation of an insoluble lead compound from solution would be able to measure the amount present? Find out what other methods are available for detecting minute traces of an element in water. Make a short list of these.
4 Given a dye which forms a bright yellow compound when lead ions are present, the depth of colour being proportional to the concentration of lead ions, devise a simple portable test kit to estimate the quantity of lead in samples of water.
5 Water filters and ion exchange columns are used in some homes to purify tap water. Find out how these work, and discuss whether either of them would remove dissolved lead from the water.
