Bromate potassium

Bromated flour bromic acid potassium salt 

Potassium bromate has been banned in several countries as a carcinogen. 

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Potassium bromate [7758-01-7] is much less soluble than the bromide and can mostly be removed by filtration the remaining bromate is reduced with iron. After filtration of the iron oxide, the KBr is crystallized. 

A similar procedure may also be used for the determination of antimony(V), whilst antimony (III) may be determined like arsenic(III) by direct titration with standard iodine solution (Section 10.113), but in the antimony titration it is necessary to include some tartaric acid in the solution this acts as complexing agent and prevents precipitation of antimony as hydroxide or as basic salt in alkaline solution. On the whole, however, the most satisfactory method for determining antimony is by titration with potassium bromate (Section 10.133). 

Potassium bromate is a powerful oxidising agent which is reduced smoothly to bromide ... 

The relative molecular mass is 167.00, and a 0.02M solution contains 3.34 g L1 potassium bromate. At the end of the titration free bromine appears ... 

Various substances cannot be oxidised directly with potassium bromate, but react quantitatively with an excess of bromine. Acid solutions of bromine of exactly known concentration are readily obtainable from a standard potassium bromate solution by adding acid and an excess of bromide ... 

Potassium bromate is readily available in a high state of purity the product has an assay value of at least 99.9 per cent. The substance can be dried at 120-150 °C, is anhydrous, and the aqueous solution keeps indefinitely. It can therefore be employed as a primary standard. Its only disadvantage is that one-sixth of the relative molecular mass is a comparatively small quantity. 

Dry some finely powdered potassium bromate for 1-2 hours at 120 °C, and allow to cool in a closed vessel in a desiccator. Weigh out accurately 3.34 g of the pure potassium bromate, and dissolve in 1 L of water in a graduated flask. 

Discussion. The antimony or the arsenic must be present as antimony(III) or arsenic(III). The reaction of arsenic(III) or antimony (III) with potassium bromate may be written ... 

To determine the purity of a sample of arsenic(III) oxide follow the general procedure outlined in Section 10.127 but when the 25 mL sample of solution is being prepared for titration, add 25 mL water, 15 mL of concentrated hydrochloric acid and then two drops of indicator solution (xylidine ponceau or naphthalene black 12B see Section 10.125). Titrate slowly with the standard 0.02M potassium bromate with constant swirling of the solution. As the end point approaches, add the bromate solution dropwise with intervals of 2-3 seconds between the drops until the solution is colourless or very pale yellow. If the colour of the indicator fades, add another drop of indicator solution. (The immediate discharge of the colour indicates that the equivalence point has been passed and the titration is of little value.)... 

Hence 1 mole of the oxinate of a double-charged metal corresponds to 4 moles of bromine, whilst that of a triple-charged metal corresponds to 6 moles. The bromine is derived by the addition of standard 0.02Af potassium bromate and excess of potassium bromide to the acid solution. 

Better results are obtained by oxidation with potassium bromate in the presence of hydrochloric acid ... 

The hydroxylamine solution is treated with a measured volume of 0.02M potassium bromate so as to give 10-30 mL excess, followed by 40 mL of 5M hydrochloric acid. After 15 minutes the excess of bromate is determined by the addition of potassium iodide solution and titration with standard Q.1M sodium thiosulphate (compare Section 10.134). 

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