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CHEMISTRY

Chemistry is the science of matter. Scientists study chemicals, their properties, and REACTIONS. BIOCHEMISTRY is the chemistry of living things.

WHAT IS A CHEMICAL?

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.

WHAT ARE CHEMICAL PROPERTIES?

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.

WHY ARE SOME CHEMICALS DANGEROUS?

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.

STRONG REACTION

Chemists use experiments to find out how chemicals react when they are mixed in different ways. Some chemicals react strongly, bubbling, burning, or even exploding. Other chemicals do not react at all.

CHEMICAL REACTIONS

A chemical reaction happens when two or more chemicals combine to make new chemical compounds. Many reactions release heat—for example, burning.

WHAT ARE ACIDS AND BASES?

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

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 14Caustic soda (oven cleaner) Caustic soda reacts with fat and grease marks, and destroys skin and flesh.
pH 11Milk of magnesiaThis alkali is used to cure indigestion—it neutralizes the acid in your stomach.
pH 9Liquid soapAll cleaning products are bases. Like most bases, soap feels slippery.
pH 7.5BloodMedical injections contain chemicals called buffers to match the pH of blood.
pH 6–7Pure waterPure water is neutral—it is neither an acid nor a base.
pH 4OrangesOranges are mildly acidic, which is why they taste slightly sharp.
pH 3VinegarThe acid in vinegar kills bacteria, so it is used in pickling to preserve food.
pH 2Lemon juiceLemons taste sour because they contain citric acid. Acid means “sour” in Latin.
pH 1Hydrochloric acidThis is a strong, corrosive acid. It eats through most metals in a fizzing reaction.

BIOCHEMISTRY

Biochemistry studies the molecules in living things, including plants, animals, and the human body. These molecules are all compounds of the element carbon.

WHY IS LIFE BASED ON CARBON?

Carbon atoms can link to each other (and to other elements) in many, many ways, including rings and chains of any length. This enormous variety means carbon is the perfect main building block for the complicated molecules of life.

FIND OUT MORE

Elements
Materials
Matter

Copyright © 2007 Dorling Kindersley

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