| 0.1M Sodium Thiosulphate |
| 1.0 Scope: This procedure is applicable for preparation and standardization of 0.1M sodium thiosulphate solution. 2.0 Apparatus: 2.1 1000 ml volumetric flask 2.2 250 ml glass-stoppered, conical flask 2.3 100 ml graduated burette 2.4 500 ml, 250 ml and 100 ml volumetric flask 2.5 50 ml volumetric pipette 3.0 Reagents: 3.1 Sodium thiosulphate AR grade 3.2 Potassium iodide AR grade 3.3 Sodium carbonate AR grade 3.4 Starch solution 3.5 Potassium Dichromate 3.6 Sodium Bicarbonate 4.0 Preparation: Dissolve 26.0 gm of sodium thiosulphate and 0.20gm or 200.0 mg of sodium carbonate in 1000.0 ml of recently boiled and cooled Purified water. To read this GTP click here Preparation and Standardization 0.1M Zinc Sulphate. 5.0 Standardization: Accurately weigh about 0.210gm or 210.0mg of Primary standard potassium dichromate(K2Cr2O7), previously dried at 120°C for 4 hours, and dissolve in 100 ml of water in a glass-stoppered, 500.0 ml flask. Swirl to dissolve the solid, remove the stopper, and quickly add 3.0 gm of potassium iodide, 2.0 gm of sodium bicarbonate(NaHCo3), and 5.0 ml of hydrochloric acid (HCl)Insert the stopper gently in the flask, swirl to mixed, and allow to standing in the dark for exactly about 10 minutes. Rinse the stopper and the inner walls of the flask with water, and titrate the liberated iodine with the sodium thiosulphate solution until the solution is yellowish green in color. By Adding 3.0ml of 1%w/v starch Test Solution, and continue the titration until the blue color is discharged. 6.0 Calculation: Wt. in mg of Potassium dichromate x potency M = —————————————————————————- 49.04 x Consume Burette Reading of sodium thiosulphate x 100 7.0 Storage: Preserve the solution in clean glass-screw bottles. |