In the experiment add HNO3 , 6 M HNO3 to sample solution for breaking NaCl into ion and drop wise AgNO3 to catch ion with Cl then the sample solution will have precipitate and stirring during drop AgNO3 because stirring can help increasing of reaction from calling of electron and when we what the mixture solution for the precipitate are crowd as have kinetic energy to help quidely reaction that take solution in dark because light can make my product lost. After filtration we use HNO3 to wash the precept ate because HNO3 can defect a contaminate in analyte finally before weigh the precipitate from drying need to leave the precipitate to cool at room temperature for nearly true value g Cl when weigh.