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Name of the Experiment Estimation of copper in the supplied solution using standardized sodium thiosulphate solution. Theory When KI is added to a solution of copper sulfate, white cuprous iodide (Cuzl2) is precipitated and an equivalent amount of iodine is liberated. This free iodine is titrated against standard solution of sodium thiosulphate using starch as an indicator. As soon as all the liberated iodine has been reduced to iodide (Nal), the blue color of starch-iodine complex will disappear and the color of precipitation in conical flask will be white due to the formation of cuprous iodide. This indicates the end point. 2CUSO4 + 4KI = Cuzl2 (1) (white ppt.) + 2K2SO4 + 2 2Na2S2O3 + I2 = Na2S4O6 + 2Nal Therefore, 2 CuSO4 = I2 = 2Na2S2O3 1 mole CuSO4 1 mole Na2S2O3 So, 1000mL of 1M Naz2S2O3 solution = 63.54 g of copper Procedure In order to estimate the copper contained by the iodometric method at first we shall have to determine the strength of sodium thiosulphate solution. Then by using the standardized sodium thiosulphate solution we will determine the amount of copper by titration. Standardization of sodium thiosulphate solution a. Preparation of 0.02 (M) K2CR2O7 solution Make a 100 mL of this solution by dissolving the calculated amount of potassium dichromate in 100 mL of distilled water in a 100 mL volumetric flask. Use electronic balance very carefully to measure the amount of potassium dichromate. b. Standardization of sodium thiosulphate using standard potassium dichromate