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).
For each of the following mixtures state whether it is a homogenous or a heterogenous mixture:
- sugar and water
- flour and iron filings (small pieces of iron)
- flour and baking powder
- smarties, jelly tots and peppermints
- This is a homogenous mixture since we cannot see the sugar in the water. Also, the two components are mixed uniformly.
- This is a heterogenous mixture since we are able to make out the pieces of iron in the flour. 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.
- Homogenous mixture since there is no way to distinguish between the flour and the baking powder. The two components of the mixture are uniformly mixed.
- Heterogenous mixture since we can clearly see each of the components that make up the mixture. The three components of the mixture are not evenly distributed.
Activity: classifying materials
Look around your classroom or school. Make a list of all the different materials that you see around you. Try to work out why a particular material was used. Can you classify all the different materials used according to their properties? On your way to school or at home or in the shops, look at the different materials that are used. Why are these materials chosen over other materials?
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. Try to make mixtures using other substances. Are the mixtures that you have made heterogeneous or homogeneous? Give reasons for your choice.
Mixtures
- Which of the following substances are
mixtures ?
- tap water
- brass (an alloy of copper and zinc)
- concrete
- aluminium
- Coca cola
- distilled water
- 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.
