How Does Potassium Bromate React?
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.
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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
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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 –
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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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FAQs on Potassium Bromate: Structure, Preparation & Uses
1. What is potassium bromate?
Potassium bromate is an ionic compound with the chemical formula KBrO₃. It is the potassium salt of bromic acid and presents as white, crystalline powder or crystals. Chemically, it is classified as a strong oxidizing agent, a property that makes it useful in various industrial and laboratory applications.
2. What are the main industrial and chemical uses of potassium bromate?
The primary use of potassium bromate is as a flour improver in the baking industry, where it functions as a dough conditioner. Its oxidizing properties help strengthen the dough, leading to better volume and texture in bread. Other important uses include:
- As a primary standard in volumetric analysis (bromometry) due to its purity and stability.
- An oxidizing agent in analytical chemistry reactions.
- A component in some formulations for permanent-wave hair treatments, although this use is less common today.
3. How is potassium bromate prepared?
Potassium bromate is commercially prepared by passing bromine (Br₂) gas through a hot, concentrated solution of potassium hydroxide (KOH). In this disproportionation reaction, bromine is both oxidized and reduced, yielding potassium bromate and potassium bromide. The overall balanced chemical equation for the synthesis is: 3Br₂ + 6KOH → KBrO₃ + 5KBr + 3H₂O. The less soluble potassium bromate can then be isolated from the solution by crystallization.
4. What is the chemical structure of potassium bromate?
Potassium bromate (KBrO₃) is an ionic compound composed of a potassium cation (K⁺) and a bromate anion (BrO₃⁻). The bromate ion has a trigonal pyramidal geometry. The central bromine atom is covalently bonded to three oxygen atoms and possesses one lone pair of electrons. This structure, along with the high oxidation state of bromine (+5), is a key factor behind its strong oxidizing capabilities.
5. How does potassium bromate work to improve bread dough?
As a potent oxidizing agent, potassium bromate modifies the protein structure in flour, specifically the gluten. It oxidizes the sulfhydryl groups (-SH) present in the gluten protein chains, causing them to form disulfide bonds (-S-S-). This cross-linking creates a stronger and more elastic gluten network. This enhanced network is more effective at trapping the carbon dioxide gas produced during yeast fermentation, resulting in a bread loaf with better volume, a finer crumb, and improved texture.
6. Why is potassium bromate considered a health risk and banned in many countries?
Potassium bromate is classified as a Group 2B carcinogen by the International Agency for Research on Cancer (IARC), meaning it is possibly carcinogenic to humans. Animal studies have linked its consumption to tumors in the kidney and thyroid. During baking, KBrO₃ is supposed to decompose into harmless potassium bromide (KBr). However, if excessive amounts are used or if the baking time or temperature is insufficient, residual potassium bromate can remain in the final food product, posing a significant health risk. Consequently, its use as a food additive is banned in many regions, including the European Union, Canada, and India.
7. What is the difference between potassium bromate (KBrO₃) and potassium bromide (KBr)?
Despite their similar names, potassium bromate and potassium bromide are fundamentally different compounds with distinct properties and uses:
- Potassium Bromate (KBrO₃): Contains the bromate ion (BrO₃⁻) where bromine has an oxidation state of +5. It is a strong oxidizing agent used as a flour improver and is a potential carcinogen.
- Potassium Bromide (KBr): Contains the bromide ion (Br⁻) where bromine has an oxidation state of -1. It is a stable salt, not an oxidizer, and is used in medicine as a sedative or anticonvulsant. In baking, KBrO₃ is intended to convert into the much safer KBr.
8. What are some safer alternatives to potassium bromate in baking?
Due to the health concerns associated with potassium bromate, the baking industry has widely adopted safer alternatives to achieve similar dough-improving effects. The most common and effective alternative is ascorbic acid (Vitamin C). Ascorbic acid also functions as an oxidizing agent in the presence of oxygen during the dough mixing process, helping to form the necessary disulfide bonds in gluten without the associated health risks of bromate.
