Bromate estimations

Principle. An organic compound which contains chlorine is mixed with sodium peroxide and ignited in a closed metal bomb. The chlorine is thus converted to sodium chloride, and after acidification the chloride is estimated by the Volhard volumetric method. Bromine and iodine, when constituents of organic compounds similarly treated, are converted largely into sodium bromate and iodate respectively these ions are therefore subsequently reduced by hydrazine to bromide and iodide ions, and estimated as before. 

Theory Potassium bromate can be estimated by the addition of potassium iodide and dilute hydrochloric acid. Thus, we have ... 

A different approach is used in the estimation of phenols. Bromine is generated by reaction of potassium bromide with a defined volume of a standard solution of potassium bromate according to the following equation ... 

A modification of this method is to effect the oxidation by a known quantity of bromine (obtained by the addition of standard potassium bromate solution together with potassium bromide and hydrochloric acid) and subsequently add excess of potassium iodide the superfluous bromine liberates a corresponding amount of iodine, which can be estimated titrimetrically hence the bromine consumed and the hydrogen sulphide oxidised can be calculated.4 The chemical change in this case is ... 

Bromate near its detection limit gave the following chromatographic peak heights and standard deviations. The blank is 0 because chromatographic peak height is measured from the baseline adjacent to the peak. For each concentration, estimate the detection limit. Find the mean detection limit. 

Estimation Gravimetrically as Sulphide as Magnesium Pyroarsenate—Volu-metrically by Iodometric Methods with Potassium Bromate, etc.—The Marsh Test—The Gutzeit Test—Fleitmann s Test—Colorimetric Methods— Microohemioal Methods—Determination of Arsenic in Gases. 

Nascent chlorine or iodine can be generated from their corresponding salts in a similar manner. For the use of standard bromate in estimations, see p. 500. 

The corresponding sodium salts, which are cheaper, serve equally well. Excess of potassium bromide and hydrochloric acid is added to a solution of the substance to be estimated and the bromate, in the form of a volumetric solution (usually N/5), is run in. The end point (shown by the presence of free bromine) is detectable, quite sharply, by spotting on starch-iodide paper as external indicator. Alternatively the end point may be determined by adding a known amount of bromate in excess, then potassium iodide, and titrating the liberated iodine with thiosulphate. 

General Procedure.—Dissolve 0-2—0-5 gm. of the compound to be estimated in 200 c.cs. of water, using a slight excess of hydrochloric acid for amines or a similar excess of caustic soda in the case of phenols, carboxylic- and sulphonic-acids. To the solution thus prepared 10 c.cs. of a 20% solution of potassium bromide and 5—10 c.cs. of concentrated hydrochloric acid are added the mixture is brought to the required temperature and N/5 bromate solution run in slowly until a sample withdrawn gives a reaction on starch-iodide paper. The presence of free bromine should be again tested for after 5 minutes. 

Undecanoic acid, 32, 104 10-Undecynoic acid, 32, 104 Unsaturation, quantitative estimation by bromate-bromide titration method, 34, 86, 89 Urea, 30, 24 31, 11 Urea, I-(T -bromophenyl)-, 31, 8 1-(o-chlorophenyl)-2-thio-, 31, 21 1,1-dimethyl-, 32, 61 I-(P-phenetyl)-, 31,11... 

Bromate frequently occurs in appreciable proportions up to 0 per cent, and is to be avoided. It gives a blue colour with potassium iodide and starch in presence of dilute sulphuric acid chlorite and hypochlorite also react with starch iodide. Chlorate gives a similar coloration on longer standing. The bromate may be estimated quantitatively by addition of potassium iodide and dilute acid, and titrating back the free iodine with thiosulphate. Specification limits vary from 0 05 to o-15 per cent. 

For the estimation of diph4nytamim the powder may be saponified as above, and then distilled until all the diphen amtne has passed over. The distillate is extracted with ether, which is separated, dried with calcium chloride and evaporated. The diphenylamine may also be estimated by conversion to tetrabromo diphcnylamine. For this purpose the ethereal solution is evaporated with atcohalcoholic solution with stirring. The tetrabromo-diphenylamine separates out, and the supernatant liquor should be dear and should smell distinctly of bromine. Water is added and the whole is boiled to remove alcohol and bromine. The bromine compound is filtered oiF, washed with warm water and dried in a steam oven. The bromination may also be ejected by potassium bromate and bromide in acid solution. 

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