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 200.mL sample of groundwater known to be contaminated with iron(II) chloride, which would react with silver nitrate solution like this: FeCl2 (aq) + 2AgNO3 (aq) → 2AgCl (s) + FeNO32 (aq) The chemist adds 75.0m 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 6.0mg of silver chloride. Calculate the concentration of iron(II) chloride contaminant in the original groundwater sample. Be sure your answer has the correct number of significant digits.

Answer 1

first write balance chemical reaction

FeCl2 (aq) + 2AgNO3 (aq) → 2AgCl (s) + FeNO32 (aq)

we use 200 mL ground water and finally she collected 6.0 mg AgCl so,

according to balance chemical reaction 1 mole of FeCl2 react with 2 mole of AgNO3 and product will be 2 mole of AgCl and 1 mole of Fe(NO3)2

we need find moles of all compound

moles of AgCl = (0.006 g / 143.32 g/mol ) = 0.00004186 moles

so, moles of FeCl2 = 0.00004186 moles / 2 = 0.00002093 moles

concentration of FeCl2 = moles / volume = 0.00002093 moles / 0.2 L = 0.00001046 M