Homogeneous Mixtures

Homogeneous Mixtures

A homogeneous mixture has a definite composition, and specific properties. In a homogeneous mixture, the different parts cannot be seen. A solution of salt dissolved in water is an example of a homogeneous mixture. When the salt dissolves, it spreads evenly through the water so that all parts of the solution are the same, and you can no longer see the salt as being separate from the water. Think also of coffee without milk. The air we breathe is another example of a homogeneous mixture since it is made up of different gases which are in a constant ratio, and which can’t be visually distinguished from each other (i.e. you can’t see the different components).

Did You Know?

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. For example steel is an alloy made up mainly from iron with a small amount of carbon (to make it harder), manganese (to make it strong) and chromium (to prevent rusting).

Definition: Homogeneous mixture

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

Example: Mixtures

Question

For each of the following mixtures state whether it is a homogeneous or a heterogeneous mixture:

1. sugar dissolved in water

2. flour and iron filings (small pieces of iron)

Step 1: Look at the definition

We first look at the definition of a heterogeneous and homogeneous mixture.

Step 2: Decide whether or not you can see the components

1. We cannot see the sugar in the water.

2. We are able to make out the pieces of iron in the flour.

Step 3: Decide whether or not the components are mixed uniformly

1. The two components are mixed uniformly.

2. In this mixture there may be places where there are a lot of iron filings and places where there is more flour, so it is not uniformly mixed.

Step 4: Give the final answer

1. Homogeneous mixture.

2. Heterogeneous mixture.

Optional Activity: Making mixtures

Make mixtures of sand and water, potassium dichromate and water, iodine and ethanol, iodine and water. Classify these as heterogeneous or homogeneous. Give reasons for your choice.

Make your own mixtures by choosing any two substances from

• sand

• water

• stones

• cereal

• salt

• sugar

Try to make as many different mixtures as possible. Classify each mixture and give a reason for your choice.

Potassium dichromate (top) and iodine (bottom)