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Updated: May 14, 2025
For example, the amount of MnO in a sample of the mineral pyrolusite may be determined by dissolving the mineral in hydrochloric acid, absorbing the evolved chlorine in a solution of potassium iodide, and measuring the liberated iodine by titration with a standard solution of sodium thiosulphate.
Make a blank test for the amount of thiosulphate solution required to react with the iodine liberated by the iodate which is generally present in the potassium iodide solution, and deduct this from the total volume used in the titration.
The iodine liberated by the reaction 2FeCl + 2HI = 2HCl + 2FeCl + I is reduced by the addition of 50 cc. of sodium thiosulphate solution and the excess thiosulphate is titrated with standard iodine and requires 7.85 cc. 45 cc. I solution = 45.95 cc. Na S O solution; 45 cc. As O solution = 45.27 cc. I solution. 1 cc. arsenite solution = 0.005160 gram As O . !Answer!: 23.77%.
Add 5 cc. of bromine water and boil until the excess of bromine is expelled. Then add 1-2 cc. of freshly prepared starch solution, and add thiosulphate solution, drop by drop, until the blue color is discharged. From the data obtained, including the "blank test" of the iodide, calculate the relation of the thiosulphate solution to the normal.
The gastro-intestinal mucous membrane is bright red in colour, owing to the presence of cyanmethæmoglobin. Hands clenched, nails blue, jaws fixed, froth about mouth. Eyes prominent and glistening, odour of acid from body, venous system gorged. Treatment. Empty the stomach by the tube at once, and wash it out with a solution of sodium thiosulphate. Strong ammonia to the nostrils.
Weigh out 25 grams of sodium thiosulphate, dissolve it in water which has been previously boiled and cooled, and dilute to 1000 cc., also with boiled water. They should, therefore, be protected from light and heat. Iodine solutions are not stable for long periods under the best of conditions.
Although this process is well known, a short description of it may not here be out of place. The process depends on the reduction of indigo to indigo-white, or soluble indigo, by means of hyposulphite, or, as it is generally termed to avoid confusion with antichlore, rightly named thiosulphate of soda, hydrosulphite of soda.
As the reaction between sodium thiosulphate and iodine is not always free from secondary reactions in the presence of even the weakly alkaline bicarbonate, it is best to avoid the addition of any considerable excess of iodine.
The reactions involved are: MnO + 4HCl > MnCl + 2H O + Cl Cl + 2KI > I + 2KCl I + 2Na S O > 2NaI + Na S O Assuming that the weight of thiosulphate corresponding to the volume of sodium thiosulphate solution used is known, what is the corresponding weight of manganese dioxide? From the reactions given above, the following proportions may be stated: 2Na S O :I = 316.4:253.9, I :Cl = 253.9:71,
A sample of pyrolusite weighs 0.2400 gram and is 92.50% pure MnO . The iodine liberated from KI by the manganese dioxide is sufficient to react with 46.24 cc. of Na S O sol. What is the normal value of the thiosulphate? !Answer!:: 0.1105 N. !Answer!: 0.08339 N.
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