Date: ……………. Page No. ….. Experiment No. 3 Name of Experiment: To find out percentage purity of a sample of hydrated ferrous sulphate FeSO4.7H2O, 31 g of which have been dissolved in 1 L of solution. M/50 solution of potassium permanganate is provided. Apparatus Required: Beaker, burette, pipette, conical flask, stand, funnel. Chemicals Required: Solution of ferrous sulphate, solution of KMnO4, sulphuric acid. Principle: Potassium permanganate oxidises ferrous ion of ferrous sulphate to ferric ion in acidic medium according to following ionic equation: πππ4− + 8 π»+ + 5e πΉπ 2+ → → ππ2+ + πΉπ 3+ + 4 π»2 π e }x5 --------------------------------------------------------------------------------------------------------------πππ4− + 5 πΉπ 2+ + 8 π»+ → ππ2+ + 5πΉπ 3+ + 4 π»2 π Procedure: Burette, pipette, conical flask and funnel were washed properly. The pipette was rinsed with ferrous sulphate solution. 20 mL of ferrous sulphate solution was taken in the conical flask with help of pipette. One test tube of dilute sulphuric solution was added to it. The burette was rinsed with given solution of potassium permanganate and then filled with this solution. Initial reading was noted. Now from the burette potassium permanganate solution was added to conical flask slowly and drop wise with regular shaking till the permanent pink colour was imparted to the solution. Final reading of burette was noted. Difference was calculated. The steps were repeated 4-5 times to get a set of three concordant readings. Observations: Volume of ferrous sulphate solution taken for each titration = 20 mL S. No. Initial Burette reading Final Burette reading 1 5 mL 25.2 mL Volume of KMnO4 solution used 20.5 mL 2 20.5 mL 40.5 mL 20 mL 3 8 mL 28 mL 20 mL 4 28 mL 48 mL 20 mL Concordant volume = 20 ml Colour change at end point = Colourless to pink (Permanganate solution was taken in the burette) Indicator used = KMnO4 acts as self-indicator Calculations: ππΎπππ4 . ππΎπππ4 ππΉπππ4 . ππΉπππ4 = 1 5 ππΎπππ4 = Molarity of πΎπππ4 = M/50 = 0.02 M ππΎπππ4 = Volume of πΎπππ4 = 20 mL 0.02 × 20 π πΉπππ4 × 20 = π πΉπππ4 = Molarity of ferrous sulphate = ? ππΉπππ4 = Volume of ferrous sulphate = 20 mL 1 5 π πΉπππ4 = 0.02 x 5 = 0.1 M Strength (g/ L) = Molarity x molecular mass = 0.1 x 278 = 27.8 g/L Percentage purity of the sample = 27.8 31 x 100 = 89.67 % Precautions: 1. The conical flask should not be rinsed. 2. Reading of upper meniscus of permanganate solution should be noted. 3. Permanganate solution should be added to conical flask only drop wise with regular shaking. 4. Correctness of end point should be checked.