Solutions decinormal, salts

Uranous Salt. — The solution of 1 gm. of uranium nitrate in 20 cc. of water and 1 cc. of dilute sulphuric acid should be colored red on the addition of 0.1 to 0.2 cc. of decinormal potassium permanganate. 

About 2 gm. benzyl iodide are weighed into a flask and then 50 ml. 20% alcoholic potash solution are added and the mixture refluxed for about an hour. At the completion of the saponification the contents of the flask are allowed to cool and then transferred to a 500-ml. flask and made up to volume with water. 100 ml. of the resulting solution are placed in a distillation flask and distilled in steam after adding 10 gm. ferric ammonium alum and acidifying with sulphuric acid. By this treatment, the ferric salt is converted to the ferrous condition, liberating iodine which is distilled over into 5% potassium iodide solution. At the end of the distillation, the free iodine in the potassium iodide solution is titrated with a decinormal solution of sodium thiosulphate. From this, the amount of iodine and so the quantity of benzyl iodide in the sample may be calculated. 

Hence, particular precautions must be taken when we prepare permanganate solutions. The most often used solution contains 1/50 mol/L (decinormal solution). They must be standardized before use. For their standardization, we can use some standard reducing inorganic substances such as ferrous salts, arsenious acid, and sodium thiosulfate. We can also use reducing organic substances such as oxalic acid and its derivatives. 

In contrast with this, the overpotential in the region with b - 60 mV is almost independent of the solution composition, both in pure acids and in acidified salt solutions. In hydrochloric acid of different concentrations, the overpotential is the same to within 3-7 mV, and no regular connection with concentration is observed. In sulfuric acid, a slow increase of 8-10 mV is observed as the acid concentration is reduced from 0.1 to O.OIN. This increase is within the limits of the experimental error, and it is possible that it may arise due to some change in the state of the surface a tendency towards a slow rise in overpotential with time is observed in dilute solutions, while no such effect is observed in decinormal acid. In any case, it is clear that within the limits of the experimental error, the overpotential in this region is independent of the solution composition. 

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