Preparation of potassium bromate
28 g of potassium hydroxide (free from potassium carbonate as possible) are dissolved in 100 ml of water. The solution is cooled to room temperature and 40 g (or 12.5 ml) of bromine are poured into potassium hydroxide solution, about 1 ml at a time. During the addition of bromine the reaction flask is stirred or rotated until the bromine has dissolved after each addition. When all the bromine is added, it should be in slight excess, which is shown by a distinct reddish tint in the solution, not merely a yellow color. The solution is heated to boiling and boiling is continued until the excess of bromine has been expelled. Then the solution is cooled to 10-15° C and obtained crystals of potassium bromate are collected by filtration. The filtrate contains a by-product crude potassium bromide, which could be used for the preparation of pure potassium bromide. The crystals of potassium bromate are dissolved in four times their weight of hot water and unless the solution is perfectly clear it should be filtered while hot. The solution is cooled below 15° C as before, and the crystals of potassium bromate are collect by filtration. If obtained potassium bromate gives silver bromide when treated with silver nitrate repeated recrystallization is required to obtain pure potassium bromate-free from potassium bromide.
Synthetic inorganic chemistry, by A. A. Blanchard, 245, 1936