Percent Yield and Purity

From last class, we knew that in real chemical reactions, chemicals are not always able to be recoverd, or some reactants will not use up. In that case, we are not possible to get same amount of products as we want according to equations.
So that we have to calculate % Yield!!!
% Yield = (grams of actual product recoverd) / (grams of products expected for stoich) * 100%





We also know that not all the chemicals are pure, 
for instance, most of the metal in earth are exist in type of alloy.
 So that we have to calculate % Purity before we solve the problems
% Purity = (Mass of pure substance) / (Mass of Impure sample) * 100%

Example:   0.1g H2 appears when sufficient Iron react with 100g HCl which the purity is 12%, what is the % Yield?

First, balance equation: Fe + 2HCl = FeCl2 + H2
100g * 12% / (36.5g/mol) * (1 mol H2/ 2 mol HCl) * 2g/ mol = 0.33g H2
% Yield = 0.1g / 0.33g * 100% = 30.3%