Calculate the concentration of tin(II) chloride contaminant in the original groundwater sample. Be sure your answer has the correct number of significant digits.

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 tin(II) chloride, which would react with silver nitrate solution like this:

SnCl2

(aq) +

 2AgNO3

(aq) →

 2AgCl

(s) +

 SnNO32

(aq)

The chemist adds 90.0m

M silver nitrate solution to the sample until silver chloride stops forming. She then washes, dries, and weighs the precipitate. She finds she has collected 8.0mg

 of silver chloride.Calculate the concentration of tin(II) chloride contaminant in the original groundwater sample. Be sure your answer has the correct number of significant digits.

Answer 1

The assumption is that the silver nitrate solution is in excess. So, the amount of precipitate is solely dependent on the amount of tin(II) chloride in solution:

.008g AgCl(1 mole/143.31 g) (1 mole SnCl₂/ 1 mole AgCl) = moles of SnCl₂

concentration in molarity is moles of SnCl₂/ .250 liters.

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