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 200. mL sample of groundwater known to be contaminated with nickel(II) chloride, which would react with
silver nitrate solution like this:
NiCl(aq) + 2 AgNO3(aq) → 2 AgCl(s) + Ni(NO3),(aq)
The chemist adds 73.0 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 6.7 mg of silver chloride.
Calculate the concentration of nickel(II) chloride contaminant in the original groundwater sample. Round your answer to 2 significant digits.