Water pipes, especially older ones, often contain lead. One example of lead prob

Question

Water pipes, especially older ones, often contain lead. One example of lead problems was in Flint, Michigan, where a change in the drinking water source led to a high concentration of lead ion in their drinking water. a. Solid lead is converted to lead (II) ion by oxidation with dissolved O_2 in the water. Write a complete balanced chemical reaction for the oxidation of lead to lead (II) in an acidic environment. b. The ratio of chloride to sulfate ions contributes to the quantity of lead ion in the water. Using the published K_sp values in Appendix C, would you want more chloride or sulfate ions present in the water to minimize the amount of dissolved lead (II) ion? Explain. c. Based on the K_sp value you calculated for PbI_2, would it be better to add iodide, chloride, or sulfate to a water supply to decrease the concentration of lead ions? Why?

Explanation / Answer

(a) The balanced reaction for oxidation of Pb to Pb^2+ in acidic medium is as follows:

2Pb(s) + O2 + 4H+ = 2Pb^2+ + 2H2O

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(b) Ksp of lead sulphate is 2.53*10^-8 and Ksp of Lead chloride is 1.70*10^-5

Lead sulphate has a higher Ksp value which means that it will precipitate from water easily than lead chloride. So, is disireable to have sulphate ions in water to minimise the lead concentration.

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(c) lead iodide has a Ksp value of the order 10^-9 which is smaller than both lead chloride and lead sulphate. Smaller the Ksp value easier it wil be to precipitate from water. So, it is better to add iodide ion in water

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