Calculate the number of moles for any compound in the balanced equation for which you know the mass. The masses of all other substances can be calculated from the mass of just one product or reactant. In the case of the balanced reaction Zn + 2AgN03 --- 2Ag + Zn(N03)2 the number of moles is given by dividing the mass of substance by the formula weight. Determine the number of moles needed to react by multiplying by moles of the known substance by the stoichiometric ratio of the unknown substance to the known substance.
FOR EXAMPLE; in Ca(OH)2 + 2 HCl → CaCl2 + 2 H2O, the stoichiometric ratio between HCl and Ca(OH)2 is 2:1 because the coefficients in front of the formulas in the balanced equation are 2 and 1, respectively. Continuing the example from the previous step, 0.13 moles of Ca(OH)2 corresponds to 0.13 x 2/1 = 0.26 moles of HCl. This represents the moles of HCl required to react with 10 grams of Ca(OH)2.
