One way the U.S. Environmental Protection Agency (EPA) tests for chloride contam
ID: 723701 • 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 sample of groundwater known to be contaminated with cadmium chloride, which would react with silver nitrate solution like this:
CdCl2 (aq) 2AgNO3 (aq) = 2AgCl (s) Cd(NO3)2 (aq)
The chemist adds M silver nitrate solution to the sample until silver chloride stops forming. He then washes, dries, and weighs the precipitate. He finds he has collected of silver chloride.
Calculate the concentration of cadmium chloride contaminant in the original groundwater sample. Be sure your answer has the correct number of significant digits.
Explanation / Answer
there are a few things that are not clear in this question 1)volume of sample analyzed 2)mass of silver chloride formed let us assume that the volume of sample analyzed be V liters (it is essential that V be in liters, if it is in any other units, plz convert it to liters) and the amount of silver chloride formed be x gms so moles of silver chloride = (mass of silver chloride/mol. wt of silver chloride) moles of silver chloride = (x/143.32) now 1 mol of silver chloride is formed by 0.5 mol of cadmium chloride so (x/143.32) moles of silver chloride will be formed by (x/286.64) moles of cadmium chloride. this (x/286.64) moles of cadmium chloride are in V liters of sample that was analyzed. so molarity of cadmium chloride contaminant = (x/286.64)/V = (x/286.64V) M so substitute x (in gms) which is the mass of silver chloride and V (in liters) which is the volume of sample analyzed to get the desired answer.
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