A 4.25 g sample of white crystals is known to contain NaCl and KNO3.The sample is fully dissolved in deionized water and an excess of AgNO3 is then added, forming a precipitate of AgCl. Upon being filtered, washed, and dried, the precipitate is found to have a mass of 3.13 g. What is the percentage by mass of NaCl in the mixture? [Na=23 g/mol, Cl=35.5 g/mol, Ag=108 g/mol]
NaCl(aq) + AgNO3(aq) --> AgCl(s) + NaNO3(aq)