Solving for a reactant in solution One way the U.S. Environmental Protection Age

Question

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 200. ml sample of groundwater known to be contaminated with cadmium chloride, which would react with silver nitrate solution like this: CdC12(aq) + 2 AgNO3(aq) 2 AgCl(s) + Cd(NOs)2(aq) The chemist adds 87.0 mM silver nitrate solution to the sample until silver chloride stops forming. He then washes, dries, and weighs the precipitate. He finds he has collected 6.2 mg of silver chloride. Calculate the concentration of cadmium chloride contaminant in the original groundwater sample. Be sure your answer has the correct number of significant digits. ng MacBook Air

Explanation / Answer

volume of sample =200ml

let the concentration of cdcl2 in water be x M

so the moles of cdcl2 = molarity* volume (in liter)

the moles of cdcl2 = x*0.2

cdcl2 + 2Agcl =2Agcl + Cd(NO3)2

1mole of cdcl2 on complete reaction forms 2 moles of Agcl so, 0.2x moles of cdcl2 will form 0.4x moles of Agcl

so, mass of Agcl as a product=6.2mg (given).

mass of Agcl=moles of Agcl* molecular weight of Agcl

6.2*10-3=143.32 * 0.4x

x=1.0881*10-4 g/L

concentration of cdcl2 in water = 0.1081 mg/L

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