DK Science & Technology: Chemistry
Chemicals are the basic types of matter. The elements, such as hydrogen and oxygen, are chemicals. So are the compounds, such as water, that are made when atoms of different elements join. Our bodies, food, and the clothes we wear are all made from chemicals.
The properties of a chemical describe what it does to other chemicals. Oxygen, for example, makes iron rust, or oxidize, so oxygen is an oxidizing agent.
Our bodies contain tens of thousands of chemicals that mix and react to give us energy and keep us alive. Toxic (poisonous) chemicals interfere with these reactions. Some chemicals are also corrosive—they eat through solid material.
A chemical reaction happens when two or more chemicals combine to make new chemical compounds. Many reactions release heat—for example, burning.
Acids are chemicals that react with metals. Strong acids, such as sulfuric, nitric, and hydrochloric acid, are very corrosive. A base is a chemical that neutralizes an acid. When acids and bases react, they form chemicals called salts. Alkalis are bases that dissolve in water.
The pH scale is a measure of acidity. Very strong acids have a pH of 1, neutral chemicals are pH 7, and strong bases, or alkalis, are pH 14.
Table 23. THE pH SCALE
|pH 14||Caustic soda (oven cleaner)||Caustic soda reacts with fat and grease marks, and destroys skin and flesh.|
|pH 11||Milk of magnesia||This alkali is used to cure indigestion—it neutralizes the acid in your stomach.|
|pH 9||Liquid soap||All cleaning products are bases. Like most bases, soap feels slippery.|
|pH 7.5||Blood||Medical injections contain chemicals called buffers to match the pH of blood.|
|pH 6–7||Pure water||Pure water is neutral—it is neither an acid nor a base.|
|pH 4||Oranges||Oranges are mildly acidic, which is why they taste slightly sharp.|
|pH 3||Vinegar||The acid in vinegar kills bacteria, so it is used in pickling to preserve food.|
|pH 2||Lemon juice||Lemons taste sour because they contain citric acid. Acid means “sour” in Latin.|
|pH 1||Hydrochloric acid||This is a strong, corrosive acid. It eats through most metals in a fizzing reaction.|
Biochemistry studies the molecules in living things, including plants, animals, and the human body. These molecules are all compounds of the element carbon.