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Acids and bases

Concentrated sulphuric acid is highly corrosive. It acts as a dehydrating agent: it removes water from any substance it comes...Read More >>Concentrated sulphuric acid is highly corrosive. It acts as a dehydrating agent: it removes water from any substance it comes into contact with. This cotton towel is made from cellulose, which contains carbon, hydrogen and oxygen. When sulphuric acid is poured on the cotton, it quickly removes the water (hydrogen and oxygen), leaving behind the black carbon.Many acids and bases are highly reactive chemicals: they easily combine with other substances in chemical reactions to form new ones. Most bases do not dissolve in water; those that do are called alkalis. A weak alkali has a bitter taste, such as the caffeine in coffee. A weak acid usually has a sharp or sour taste, like the citric acid in citrus fruits such as lemons. Strong, or concentrated, acids and alkalis are so reactive that they are corrosive: they dissolve substances—including human skin—to cause severe chemical burns. Examples are the sulphuric acid in a car battery and the alkali sodium hydroxide (caustic soda), which is used as a drain-cleaner.



Mono Lake is a large, shallow lake in California, USA. It has no outlet to the sea, which causes high levels of salts to build up...Read More >>Mono Lake is a large, shallow lake in California, USA. It has no outlet to the sea, which causes high levels of salts to build up in the lake. These salts make the lake water alkaline. Columns of tufa, a kind of limestone, are formed when waters rich in carbonates flow into the alkaline lake.

Donors and receptors

Acids are substances with hydrogen in their molecules. For example, sulphuric acid is H2SO4 and hydrochloric acid is HCl. In solution with water, the hydrogen forms a positive ion: an atom without its electron. An acid is reactive because it is always ready to give up, or donate, this proton in a chemical change in order to become neutral. Alternatively, the acid can accept an electron, which is negative, to achieve the same result. For this reason, acids are known as proton donors or electron receptors. An alkali does the opposite, and so is a proton receptor or electron donor.

Phosphoric acid is used as a rust remover—and also as a flavouring in cola drinks.

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