Classification of matter  (Page 3/11)

Homogeneous mixture

A homogeneous mixture is one that is uniform, and where the different components of the mixture cannot be seen.

An alloy is a homogeneous mixture of two or more elements, at least one of which is a metal, where the resulting material has metallic properties. Alloys are usually made to improve the properties of the elements that make them up. For example steel is much stronger than iron (which is the main component of steel).

Activity: classifying materials

Activity: making mixtures

Mixtures

1. Which of the following substances are mixtures ?
   1. tap water
   2. brass (an alloy of copper and zinc)
   3. concrete
   4. aluminium
   5. Coca cola
   6. distilled water
2. In each of the examples above, say whether the mixture is homogeneous or heterogeneous.
   

Pure substances: elements and compounds

Any material that is not a mixture, is called a pure substance . Pure substances include elements and compounds . It is much more difficult to break down pure substances into their parts, and complex chemical methods are needed to do this.

One way to determine if a substance is pure is to look at its melting or boiling point. Pure substances will have a sharply defined melting or boiling point (i.e. the melting or boiling point will be a single temperature rather than a range of temperatures.) Impure substances have a temperature range over which they melt or boil. We can also use chromatography to determine if a substance is pure or not. Chromatography is the process of separating substances into their individual components. If a substance is pure then chromatography will only produce one substance at the end of the process. If a substance is impure then several substances will be seen at the end of the process.

Activity: smartie chromatography

You will need filter paper (or chromatography paper), some smarties in different colours, water and an eye dropper.

Place a smartie in the center of a piece of filter paper. Carefully drop a few drops of water onto the smartie. You should see rings of different colour forming around the smartie. Each colour is one of the individual colours that are used to make up the colour of the smartie.

Elements

An element is a chemical substance that can't be divided or changed into other chemical substances by any ordinary chemical means. The smallest unit of an element is the atom .

Element

An element is a substance that cannot be broken down into other substances through chemical means.