Decinormal solutions

Two loo-ml. burettes are filled with the gas to be examined in one the chlorine is absorbed with a solution of potassium iodide and the iodine liberated is determined by titration with a decinormal solution of sodium thiosulphate in the second burette both the chlorine and the carbon dioxide are absorbed by sodium hydroxide solution, and the difference in the diminutions of volume in the two burettes gives the volume of the carbon dioxide. 

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. 

The solution for examination should not contain more than 0-05 gm. hydrocyanic acid. It is treated with a few ml. of sodium hydroxide solution and 0-5 gm. sodium bicarbonate, and is then titrated with a decinormal solution of iodine until a yellow colour persists. In this case it is unnecessary to use starch as indicator ... 

In carrying out this determination, a weighed quantity of cyanogen bromide is treated with an excess of hydriodic acid solution, which is prepared by dissolving 10 gm. potassium iodide in 100 ml. of a 5% solution of acetic acid. The iodine liberated is titrated with a decinormal solution of sodium thiosulphate. 

The contents of the flask are then boiled, being taken almost to dryness and taken up with water several times (generally twice) so as to remove the hydrogen peroxide completely. The residue is diluted once more with 50 ml. water and a solution of sodium carbonate added until a slight precipitate is formed, this being then redissolved with a few drops of dilute acetic acid. Excess potassium iodide is added and the liberated iodine is titrated with a decinormal solution of sodium thiosulphate. 

Determination of Chlorosulphonic Acid. About i gm. of the sample is introduced into a small glass bulb which is then sealed in the flame and weighed accurately. This bulb is then placed in a tall glass cylinder of about 150 ml. capacity, containing about 100 ml. water. The cylinder is stoppered tightly and shaken violently so as to break the bulb, and then allowed to stand until the cloud which first forms in the cylinder completely disappears. The contents are then transferred to a 500 ml. flask and made up to volume. 200 ml. of the solution are then titrated with a decinormal sodium hydroxide solution, to the methyl-orange end-point, so as to obtain the total hydrochloric and sulphuric acid content. In another 200 ml. the hydrochloric acid is titrated with a decinormal solution of silver nitrate in presence of a few drops of potassium chromate solution, after addition of excess of pure calcium carbonate. 

A sample of phenyl dichloroarsine is weighed accurately, treated with water and alcohol and then titrated, without adding any sodium bicarbonate, with a decinormal solution of iodine, until the yellow colour is permanent. The number of ml. of iodine solution employed multiplied by o>oiii5 gives the amount of phenyl dichloroarsine (in gm.) in the sample. 

Such a combination yields quite an appreciable emf, the electrode in contact with the decinormal solution being in this case the positive pole, i e current flows inside the cell from right to left The nett emf of this cell depends on the three single P D s, namely, the P D, Ag ... 

For each compound listed, the last column of this table gives the mass in grams which is contained in 1 liter of a solution whose amount-of-substance concentration divided by the equivalence factor of the compound equals 0.1 mol/L. In the older literature such a solution is often referred to as a decinormal solution (0.1 N). 

A standard solution containing in a litre of liquid a number of grams of the active substance, equal to its molecular weight, i,s a normal solution one containing that amount is a decinormal solution. 

A 6 per eent. solution of hydrochloric acid. (2.) A decinormal solution of sodium thiosulphate. 

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. 

Decimal equivalents of common fractions, A-2 Decinormal solutions... 

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