One way the U.S. Environmental Protection Agency (EPA) tests for chloride contam
ID: 499868 • 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 chemist tests a 250. mL sample of groundwater known to be contaminated with iron(III) chloride, which would react with silver nitrate solution like this: FeCl_3(aq) + 3 AgNO_3(aq) rightarrow 3 AgCl(s) + Fe(NO_3)_3 (aq) the chemist adds 77.0 mM silver nitrate solution to the sample until silver chloride stops forming. She then washes, dries, and weighs the precipitate. She finds she has collected 5.2 mg of silver chloride. Calculate the concentration of iron(III) chloride contaminant in the original groundwater sample. Be sure your answer has the correct number of significant digits.Explanation / Answer
Balanced equation:
FeCl3 + 3 AgNO3 ====> Fe(NO3)3 + 3 AgCl
5.2 mg of silver chloride = 5.2 / 143.32 = 0.03628 Milli Moles
Milli Moles AgCl produced over the reaction = 0.03628
Milli Moles FeCl3 was present in 250 ml solution = 0.03628 / 3 = 0.01209 Milli Moles
Concentration of FeCl3 solution = 0.1209 x 1000 /250 = 0.04837 mM
Concentration in mg /Liter = 0.04837 X 162.204 = 7.845 mg/Liter
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