Sodiumhypochlorite,NaClO,0.50M.PDFVIP

Finding the Ratio of Moles of Reactants in a Chemical Reaction A balanced chemical equation gives the mole ratios of reactants and products for chemical reactions. If the formulas of all reactants and products are known, it is relatively easy to balance an equation to fnd out what these mole ratios are. When the formulas of the products are not known, experimental measurements must be made to determine the ratios. This experiment uses the method of continuous variations to determine the mole ratio of two reactants. Several steps are involved. First, solutions of the reactants are prepared in which the concentrations are known. Second, the solutions are mixed a number of times using diferent ratios of reactants. Third, some property of the reaction that depends on the amount of product formed or on the amount of reactant that remains is measured. This property may be the color intensity of a reactant or product, the mass of a precipitate that forms, or the volume of the gas evolved. In this experiment the change of temperature is the property to be measured. The reactions are all exothermic, so the heat produced will be directly proportional to the amount of reaction that occurs. Since the experiment is designed so that the volume of solution is a constant for all measurements, the temperature change will also be proportional to the quantity of reactants consumed. In the method of continuous variations, the total number of moles of reactants is kept constant for the series of measurements. Each measurement is made with a diferent mole ratio of reactants. The optimum ratio, which is the stoichiometric ratio in the equation, should consume the greatest amounts of reactants, form the greatest amount of product, and generate the most heat and maximum temperature change. Chemicals Sodium hypochlorite, NaClO, 0.50 M Sodium thiosulfate, Na2S2O3, 0.50 M in NaOH, 0.20 M or Potassium iodide, KI, 0.50 M