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Hydrogen Peroxide

Hydrogen peroxide, H2O2, is a colorless liquid that mixes with water and is widely used as a disinfectant and a bleaching agent. It is unstable and decomposes (breaks down) slowly to form water and oxygen gas. Highly concentrated solutions of hydrogen peroxide are powerful oxidizing agents and can be used as rocket fuel.

Hydrogen peroxide is most widely found in homes in brown bottles containing 3% solutions (3% hydrogen peroxide and 97% water). The decomposition of hydrogen peroxide happens much faster in the presence of light so that an opaque bottle helps slow this process down. The decomposition of hydrogen peroxide can be summarized by the chemical equation:

which states that two molecules of hydrogen peroxide break down to form two molecules of water and one molecule of oxygen gas, along with heat energy. This process happens slowly in most cases, but once opened a bottle of hydrogen peroxide will decompose more rapidly because the built-up oxygen gas is released. A totally decomposed bottle of hydrogen peroxide consists of nothing but water. Old unopened bottles of hydrogen peroxide often bulged out from the pressure of the oxygen gas that has built up over time. Some bottles have been known to "pop" from that pressure of the oxygen gas.

The most common uses of hydrogen peroxide are as a bleaching agent for hair and in the bleaching of pulp for paper manufacturing, and as a household disinfectant. As a bleach, hydrogen peroxide is an oxidizing agent (a substance that accepts electrons from other molecules). It is becoming more widely used than chlorine bleaches in industries because the products of its decomposition are water and oxygen while the decomposition of chlorine bleaches produces poisonous chlorine gas.

As a disinfectant, hydrogen peroxide is widely used on cuts and scrapes, and produces bubbling (caused by the formation of oxygen gasmolecules). The bubbling is quite rapid on cuts because of the presence of an enzyme (a protein catalyst—or molecule that speeds up a reaction) in blood, known as catalase. A similar bubbling can be observed if a small amount of hydrogen peroxide is put on a raw sliced potato, as the enzyme catalase is also found in potatoes.

Additional topics

Science EncyclopediaScience & Philosophy: Hydrazones to Incompatibility