Since stoichiometry studies the relations between the quantities of reactants involved and products resulted by a chemical reaction, the law of conservation of mass is the base of stoichiometry.
Since the law of conservation of mass indicates that the matter changes from one form to another, hence, based on this principle, the mass of reactants used in a chemical reaction needs to be equal to the mass of products resulted from reaction.
The problems that request for you to find the certain amouns of reactants or products can use stoichiometry laws, the balanced chemical equations and mole ratios. to mass conversions
You may perform three types of stoichiometric calculations called conversions, such that: mass to mass conversion, mole to mole conversion, mole to mass conversion.