[Chemistry Class Notes] on Potassium Bromate Pdf for Exam

Potassium bromate is an ionic compound or salt which is formed of K+ and BrO3–. It is an inorganic compound. It is a strong oxidizing agent and in India widely used in making bread. 

According to a report 84% of various types of bread products contain potassium bromate. Using potassium bromate in breads is very harmful for us as potassium bromate is carcinogen. It is banned in japan, china, UK, Canada, Brazil, Australia and New Zealand. India has also limited its use in food products. Its legal limit in India is 50 parts per million. 

Thus, potassium bromate is a white crystalline powder which acts as a strong oxidizing agent and is a bromate of potassium. Potassium bromate is also known by other names such as bromic acid or potassium salt. 

Formula of Potassium Bromate 

Structure of Potassium Bromate 

It is an ionic compound which is formed by the ionic bond between potassium ion (cation) and bromate ion (anion). It shows hexagonal crystal structure. 

Properties of Potassium Bromate 

Properties of potassium bromate are listed below –

• It is found as white crystalline powder. 

• It is a strong oxidizing agent.

• Its molar mass is 167 g.mol-1.

• Its density is 3.27 g.cm-3.

• Its melting point is 350 ℃.

• Its boiling point is 370 ℃.

• It decomposes at higher temperatures. 

• It is soluble in water. As the temperature increases, its solubility in water also increases. For example, at 0 ℃ temperature, 3.1 gram of potassium bromate is soluble in 100 ml of water while at 40 ℃ temperature, 13.3 grams of potassium bromate soluble in 100 ml of water. It reacts violently with water. 

• It is insoluble in acetone. 

• Its crystal structure is hexagonal. 

• Its non – flammable substance. 

• Its 157 mg/kg oral dose can be lethal. 

• It is a carcinogenic substance. 

• Its pH is in the range of 5 – 9 at 25 ℃ temperature. 

Preparation of Potassium Bromate 

It is produced by using bromine gas and potassium hydroxide. When bromine gas is passed over the hot potassium hydroxide, it produces potassium hypobromite. Potassium hypobromite on disproportionation gives potassium bromate. Potassium bromide and water are produced as byproducts. Reaction is given below –

3Br2 + 6KOH 🡪 KBrO3 + 5KBr + 3H2O

Another method of preparation of potassium bromate includes electrolysis of potassium bromide solution. On electrolysis of aqueous solution of KBr, potassium bromate is obtained. As at 0 ℃ temperature, potassium bromide shows very much higher solubility than potassium bromate so, after the formation of potassium bromate, solution is cooled to 0 ℃ and all potassium bromate gets precipitated while all potassium bromide remains in the solution. 

These both the methods of production of potassium bromate are very much similar to the production of chlorates. 

Uses of Potassium Bromate 

Potassium bromate is used in baking as an additive. It has been used as an oxidizing agent and dough conditioner commercially for making breads since 1923. It improves baking properties of flours/ doughs by strengthening the wheat gluten network. Thus, it improves gas retention in baked foods and increases their volume. Till 1980s and 1990s, it was used at large scale by most of the countries but recently its usage has dropped due to its carcinogenic properties. 

Its oxidizing nature is the reason of its use as an additive in baking products. It oxidizes sulfhydryl groups of proteins and forms disulfide bridges by joining two molecules of protein. Thus, it helps in cross linking pf protein molecules. This cross linking of protein molecules helps in trapping the gas evolved during baking process more effectively. Action of potassium bromate in protein cross linking is shown below by a diagram –

Protein chain 1 and 2 become a larger protein molecule by cross linking.

If the baking of dough is not done completely at high enough temperature then a residual amount of potassium bromate will be left in the baked product and if it is consumed raw then being a carcinogen, it is very harmful for health. 

It can also be used in the production of malt barley but during its usage in malt production as well guidelines by food and drug administration must be followed. 

It has been banned by many countries to use it as a food additive after the report of its carcinogenic properties. According to a study in Japan, potassium bromate causes cancer in rats and mice so it can cause cancer in humans as well. Further studies are still going on. 

India has also given the guidelines for its limited use. According to FSSAI, the legal limit of potassium bromate as a food additive is 50 parts per million. Potassium bromate has been removed from the list of permissible additives by FSSAI. 

Potassium Bromate: Summary in Tabular Form 

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