Chemistry 2

Stoichiometry With Solutions

  1. As in all other stoichiometry problems, solutions problems also boil down to determining the moles of one substance, using the chemical equation to get the mole ratio between two substances, and determining the number of moles of the other substance.
  2. For example, we might need to calculate the concentration of silver thiosulfate in used photographic solutions to determine if it should be considered hazardous waste. To do that we could react the silver thiosulfate with sodium chloride in the following reaction:

    Ag2S2O3(aq) + 2 NaCl(aq) ---> 2 AgCl(s) + Na2S2O3(aq)

    1. If you got 15.8 g of AgCl from 250.0 mL of Ag2S2O3 solution, what was the concentration of that solution:
    2. First we must convert the grams to moles.

    3. Then, set up a mole ratio:
      x       0.244    
      Ag2S2O3 + 2 NaCl ---> 2 AgCl + Na2S2O3



    4. Then, convert the moles to molarity .

  3. There are lots of different ways molarity could be used in in stoichiometry. Try these problems as well:
  4. PbNO3(aq) + 2 Cl-1(aq) ----> PbCl2(s) + NO3-1(aq)
    1. Determine the concentration of chloride ion in a water sample if the sample volume was 25.0 mL and was reacted with 85.0 mL of 0.10M PbNO3 solution. Click here for answer.
    2. What volume of 0.50 M PbNO3 would be necessary to produce 1.34 grams of PbCl2?