text: mass percent using two algebraic equations? a sample of a mixture containing only sodium chloride and potassium chloride has a mass of 6.4100g. when this sample is dissolved in water and excess silver nitrate is added, a white precipitate (silver chloride) forms. after filtration and drying, this precipitate has the mass 12.7559g. what is the mass percentage of sodium chloride in the mixture? your two basic algebraic equations are: moles na + moles k = moles cl  (g na+) + (g k+) + (g cl-) = 6.4100 g  the mass of the final precipitate means that there are 7.50921 x 10-2 mol of chloride ions present in the initial mixture. see: mol cl = mol agcl = g agcl/mw agcl = 12.7559/169.87 = 7.50921 x 10 -2 mol  the mass of the chloride component of the starting materials is then determined by:  g cl = mw cl x mol cl = (7.50921 x 10-2 mol) x (35.45 g/mol) = 2.662 g  plug that back into the second eqn and you get:  (g na+) + (g k+) + (2.662 g) = 6.4100 g or (g na+) + (g k+) = 3.748 g  convert back to moles and plug that into the first equation and you get:  moles na + moles k = 7.50921 x 10 -2 mol or moles na + ((g k+) / (39.1 g/mol)) = 7.50921 x 10 -2 mol or ((g na+) / (22.99 g/mol)) + ((3.748 - g na+) / (39.1 g/mol)) = 7.50921 x 10 -2 mol  and now solve for g na +   divide that by 3.748 g and you're there!