One way the U.S. Environmental Protection Agency (EPA) tests for chloride contam
ID: 943589 • Letter: O
Question
One way the U.S. Environmental Protection Agency (EPA) tests for chloride contaminants in water is by titrating a sample of silver nitrate solution Any chloride anions in solution will combine with the silver cations to produce bright white silver chloride precipitate. Suppose an EPA clients t tests a 250 mL sample of ground water known to be contaminated with calcium chloride, which would react with nitrate solution like this: CdCl_2(aq) + 2 AgNO_3(aq) implies 2 AgCl(s) + Cd(NO_3)_2(aq) The chemist adds 72.0 mM silver nitrate solution to the sample until silver chloride stops forming. He then washes, dries, and weighs the precipitate He finds. he has collected 3 1 mg of silver chloride. Calculate the concentration of cadmium chloride contaminant in the original groundwater sample. Round your answer to 2 significant digits.Explanation / Answer
Molar mass of AgCl = 108 + 35.5 = 143.5 gm/mol
Number of moles of AgCl = 3.1 mg/143.5 = 0.021602 m moles of AgCl
Number of moles of CaCl2 = 1/2 * number of moles of AgCl = 0.010801m moles
Molar mass of CaCl2 = 40 + 2 * 35.5 = 111 gm/mol
Mass of CaCl2 present = 0.010801m * 111 = 1.1989 mg
Since 1.1989mg is present in 250 mL, hence the concentration of CaCl2 in 1L of solution = 1.1989/0.250 = 4.7956 mg/L
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