UNIT 6 NATURAL SCIENCE: MATTER

What is matter?

Matter is made up of one or more substances which, in turn, consist of tiny particles, called atoms. Wood, plastic, air, water, oxygen and diamonds are examples of substances.

There are two types of matter:

• Pure substances. These contain only one type of component which cannot be separated into other substances. For example, water, oxygen, salt, diamonds, gold and other minerals are pure substances.
• Mixtures. These contain two or more pure substances. For example, sea water is made up of water and salts, and rocks are made up of two or more minerals.

o  Heterogeneous mixtures. In these mixtures, the different components can be distinguished.

o   Homogeneous mixtures or solutions. In these mixtures, the different components cannot be distinguished.

SEPARATION OF MIXTURES

PHYSICAL  CHANGES: CHANGES OF STATE

Matter exists in three different states: solid, liquid and gaseous. Heating or cooling can cause changes of state.

Melting and boiling points

 

Every substance changes from a solid to a liquid at a fixed temperature. This temperature is known as the melting point. For example, the melting point of water is 0 ºC, whereas gold has a melting point of 1,064 ºC and mercury has a melting point of -39 ºC.

In addition, every substance changes from liquid to gas at a fixed temperature. This temperature is known as the boiling point. For example, the boiling point of water is 100 ºC, whereas alcohol has a boiling point of 78 ºC and mercury has a boiling point of 357 ºC.

CHEMICAL CHANGES

Chemical changes happen when the original matter transforms into other new substances. These changes involve chemical reactions in which atoms react and group together differently. There are many types of chemical reactions, for example:

• Oxidation happens when some metal substances, such as iron, combine with oxygen in the presence of water. As a result, rust is produced.
• Combustion happens when objects or substances are burned. This type of reaction also needs oxygen and produces gases (usually carbon dioxide), light and heat. For example, burning wood produces light, heat, smoke (with carbon dioxide) and ashes.
• Fermentation is a chemical reaction that happens in some living things, such as yeast and bacteria. Some types of fermentation are used to produce yoghurt, wine or bread.