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Then run in the permanganate solution from a pipette or burette to determine roughly the amount required. Strong sulphuric acid also decomposes the oxalic acid. The excess of ferrous iron may also be determined by titration with potassium bichromate, if desired. The chlorine generated by the pyrolusite is passed into a solution of potassium iodide.
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.
From the corrected volume of the solution required, calculate the amount of oxalic acid undecomposed by the pyrolusite; subtract this from the total quantity of acid used, and calculate the weight of manganese dioxide which would react with the balance of the acid, and from this the percentage in the sample.
KMnO = 0.2004 gram Na C O . Calculate the percentage of sulphide sulphur in the sample. !Answer!: 0.050%. What weight of pyrolusite containing 89.21% MnO will oxidize the same amount of oxalic acid as 37.12 cc. of a permanganate solution, of which 1 cc. will liberate 0.0175 gram of I from KI? !Answer!: 0.2493 gram.
Pyrolusite, when pure, consists of manganese dioxide. Its value as an oxidizing agent, and for the production of chlorine, depends upon the percentage of MnO in the sample.
If the pyrolusite under examination is known to be of high grade, say 80 per cent pure, or above the calculation of the oxalic acid needed may be based upon an assumption that the mineral is all MnO . If the quality of the mineral is unknown, it is better to weigh out three portions instead of two and to add to one of these the amount of oxalic prescribed, assuming complete purity of the mineral.
!Answer!: 20.08 cc. !Answer!: 5.70 cc. A sample of pyrolusite weighing 0.6000 gram is treated with 0.9000 gram of oxalic acid. What is the percentage of MnO , in the sample? !Answer!: 84.47%. A solution contains 50 grams of KHC O .H C O .2H O per liter. In the analysis of an iron ore containing 60% Fe O , a sample weighing 0.5000 gram is taken and the iron is reduced with sulphurous acid.
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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