One example of a mass-to-mass stoichiometry problem is using the formula LiOH + HBr --> LiBr + H2O to determine the amount of LiBr produced when beginning with 10 grams of LiOH. Mass-to-mass stoichiometry problems typically involve determining the mass of one compound given the mass of another.
A mass-to-mass stoichiometry problem requires a balanced chemical equation. For example, a problem using the equation FeS2 + O2 ? Fe2O3 + SO2 must be balanced as 4 FeS2 + 11 O2 ? 2 Fe2O3 + 8 SO2. Next, the value in grams must be converted to moles. For example, a problem using the formula K2O + H2O --> 2KOH where the number of grams of H2O is 5.72 must convert the 5.72 grams of H2O to 0.31 moles of H2O. Mass-to-mass stoichiometry problems use the coefficients of each compound to determine the ratio of moles. For example, the coefficients in the equation C3H8 + 5 O2 --> 3 CO2 + 4 H2O are 1:5:3:4.
Another example of a mass-to-mass stoichiometry problem is determining the amount CO2 produced by the combustion of 15 grams of propane, as in the equation C3H8 + 5 O2 --> 3 CO2 + 4 H2O. Another example is using the formula Fe2O3 + 6 HCl --> 2 FeCl3 + 3 H2O to determine the amount of HCl needed to produce 15.5 grams of FeCl3.