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 sample of groundwater known to be contaminated with cadmium chloride, which would react with silver nitrate solution like this: (aq) (aq) (s) (aq) The chemist adds M silver nitrate solution to the sample until silver chloride stops forming. He then washes, dries, and weighs the precipitate. He finds he has collected of silver chloride. Calculate the concentration of cadmium chloride contaminant in the original groundwater sample. Round your answer to significant digits.

Answer 1

Answer: Molarity of CdCl2 contaminant in the original groundwater sample = (m/286.64v) mol/L

so substitute m (in gms) which is the mass of silver chloride

and

v (in liters) which is the volume of sample analyzed to get the desired answer.

Explanation: The number of moles of AgCl formed = mass/(molar mass)

Molar mass of AgCl = 143.32 g/mol, mass of AgCl formed = m

Number of moles of AgCl formed = (m/143.32) moles

But, 2 moles of AgCl was produced from 1 mole of CdCl2 contaminant according to the chemical reaction;

So, (m/143.32) moles of AgCl would produce ((m/143.32)/2) moles of CdCl2 = (m/286.64) moles of CdCl2

To get the concentration of contaminant in the groundwater sample, we will need the molarity of CdCl2 contaminant in the groundwater

Molarity = number of moles/volume in litres

Molarity of CdCl2 = ((m/286.64)/v) mol/L

Molarity of CdCl2 = (m/286.64v) mol/L

so substitute m (in grams) which is the mass of silver chloride

and

v (in liters) which is the volume of sample analyzed to get the desired answer.