Potassium bromide (KBr) is a salt, used as an anticonvulsant and a sedative in the 1800s. Today it is used in photography and as a medication for dogs (see below). In a dilute aqueous solution, potassium bromide tastes sweet, at higher concentration it tastes bitter, and when most concentrated it tastes salty to humans. As it can be harmful, testing on oneself is discouraged.

Chemical properties

Potassium bromide is a typical ionic salt which is fully dissociated and pH7 in aqueous solution. It reacts as a source of bromide ions- this reaction is important for the manufacture of silver bromide for photographic film:

KBr(aq) + AgNO₃(aq) → AgBr(s) + KNO₃(aq)

It will also form complexes when reacted with some metal halides such as copper(II) bromide :

2 KBr(aq) + CuBr₂ (aq) → K₂[CuBr₄](aq)

Preparation

A traditional method for the manufacture of KBr is the reaction of potassium carbonate with a bromide of iron, Fe₃Br₈, made by treating scrap iron under water with excess Br₂:

4 K₂CO₃ + Fe₃Br₈ → 8 KBr + Fe₃O₄ + 4 CO₂

Uses

Potassium bromide is currently used as an anti-seizure medication for dogs. It is often used as a supplement to phenobarbital if seizures are not being successfully controlled with phenobarbital alone. Increasingly, however, it is being considered as a first-line treatment. Potassium bromide is not approved by the FDA for use in humans to control seizures. An advantage of potassium bromide over phenobarbital is that it does not carry a risk of liver damage over a long period of time. A disadvantage is that it can take 3-4 months before full effectiveness is achieved.

Potassium bromide is used extensively in photography (see "chemical properties"). It is also sometimes used as a bromide source in organic synthesis, since it is less hygroscopic than sodium bromide. In the laboratory it is commonly used in infrared spectroscopy. The sample to be tested is crushed up with a large excess of KBr, and then the mixture is crushed to form a tablet which is inserted into the spectrophotometer.

Precautions

During handling, gloves and goggles are commonly worn. Tasting or swallowing is discouraged, unless KBr is prescribed by a qualified doctor.

References

1. N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, Pergamon Press, Oxford, UK, 1984.
2. Handbook of Chemistry and Physics, 71st edition, CRC Press, Ann Arbor, Michigan, 1990.
3. The Merck Index, 7th edition, Merck & Co., Rahway, New Jersey, 1960.
4. H. Nechamkin, The Chemistry of the Elements, McGraw-Hill, New York, 1968.
5. Taylor, Rattray Gordon. The Natural History of the Mind. ISBN 0-525-16424-3, 1979 E. P. Dutton. pp.181

External Resources

• Suppliers/Manufacturers
  • Fisher
  • VWR
  • Strem
  • Alfa
  • Sigma-Aldrich
  • Spectrum
• Potassium bromide handout