One way the US. Environmental Protection Agency (EPA) tests for chloride contami
ID: 482080 • Letter: O
Question
One way the US. Environmental Protection Agency (EPA) tests for chloride contaminants in water is by titrating a sample of silver nitrate solution. Any anions in solution will combine with the silver to produce bright white silver chloride precipitate. Suppose an EPA chemist tests a 200. mL sample of groundwater known to be contaminated with nickel(II)chloride, which would react with silver nitrate solution like this: The chemist adds 82.0 mM silver nitrate solution to the sample until silver chloride stops forming. She then washes, and weighs the precipitate. she finds she has collected 8.0 mg of silver chloride.Explanation / Answer
NiCl2 (aq) + AgNO3 (aq) ----> AgCl(aq) + Ni(NO3)2 (aq)
Mass of AgCl formed = 8mg = 0.008 g
Moles of AgCl formed = 0.008g/143.32g/mol =5.58*10^-5 mol
According to the above balanced equation 1 mol of NiCl2 is formed from 1 mol AgCl.
Moles of NiCl2 present in 200mL = 5.58*10^-5 mol
Mass of NiCl2= 5.58*10^-5 mol * molar mass
= 5.58*10^-5 mol * 129.59g/mol = 7.23 *10^-3 g
= 7.23 mg
Mass of NiCl2 in 1000mL = 7.23mg * 5 = 36.17 mg
Concentration of NiCl2 in ground water is 36.17 mg/L
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