It is desired to know the % purity of CUSO4*5H2O in a sample of crystals obtained during the solar evaporation of a solution containing copper sulphate, zinc and magnesium sulfate. There are 18.2 g of crystals from here, 0.524 g of crystals are extracted and dissolved in distilled water, later the solution is placed in a measuring flask and 10 ml of aliquot are extracted to determine the copper content by iodometry, they are spent 4.5 mL of a 0.02 N Na2S2O3 solution to the end point of the test. Determines the % purity expressed as % CuSO4*5H20