the chemist adds 11mM silver nitrate solution to the sample until silver chlorid
ID: 701063 • Letter: T
Question
the chemist adds 11mM silver nitrate solution to the sample until silver chloride **(the answer is in mg/L)** O CHEMICAL REACTIONS Solving for a reactant in solution 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 iron(II) chloride, which would react with silver nitrate solution like this: FeCl 2(aq) + 2 AgNO3(aq) 2 AgCl (s) + Fe(NO3) 2(aq) The chemist adds 11.0 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 6.4 mg of silver chloride. Calculate the concentration of iron(!I) chloride contaminant in the original groundwater sample. Round your answer to 2 significant digits. 00-10Explanation / Answer
FeCl2 + 2AgNO3 2AgCl + Fe(NO3)2
Moles of AgCl = mass/molecular weight
= 6.4 mg/ 143.32 mg/mmol
= 0.04465 mmol
From the stoichiometry of the reaction
2 mmol of AgCl formed from = 1 mmol of FeCl2
0.04465 mmol of AgCl formed from = 1*0.04465/2
= 0.02232 mmol of FeCl2
Mass of FeCl2 = moles x molecular weight
= 0.02232 mmol x 126.751 mg/mmol
= 2.83 mg
Concentration of FeCl2 = mass of FeCl2/volume of solution
= 2.83 mg/0.250L
= 11.32 mg/L
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