Divide Grams by Grams per Mole Divide the number of grams of each reactant by the number of grams per mole for that reactant. 50.0 g of Na are used in this reaction, and there are 22.990 g/mol. 50.0 ÷ 22.990 = 2.1749. 2.1749 moles of Na are used in this reaction.