Science 8th grade
UNIT 8: Mixtures 8.1 Compounds and mixtures
Science 8th grade
UNIT 8: Mixtures 8.1 Compounds and mixtures
We have seen that, when atoms of elements bond tightly together to form compounds, the properties of the compound are completely different from those of the elements that it is made from.
For example, iron is a metal. It is hard, coloured grey, strong, conducts heat and electricity and is magnetic.
Sulfur is a non-metal. It is yellow, brittle, does not conduct heat or electricity and is not magnetic.
When these two elements are heated they combine together to form the compound iron sulfide. Iron sulfide is not magnctic and does not conduct heat or electricity.
.The sulfur, shown here as powder, is yellow and not hard
Activity 8.1A (Mixing iron and sulfur)
SE: Safety: Do not touch your face or eyes after touching the iron filings. The pieces have sharp edges and can damage your skin and eyes.
Wear safety glasses.
1) Place some iron filings in a beaker.
2) Add some yellow powdered sulfur.
3) Stir the mixture.
You now have a mixture of iron and sulfur. The iron and sulfur still have their properties. They have not been changed chemically in any way.
The different properties of the two elements can be used to separate them from the mixture.
4) Use a magnet to remove the iron filings from the sulfur.
Activity 8.1B (Making a compound from iron and sulfur)
SE: 1) Make a mixture of iron and sulfur.
Safety: Wear safety glasses. Carry this out in a well-ventilated room.
2) Heat some of the iron and sulfur mixture in a boiling tube, as in the photograph on the opposite page. Stop heating as soon as the mixture starts to glow. The iron and sulfur will combine together and form iron sulfide.
3) Leave the tube to cool.
4) Test with a magnet.
Questions
${A_1}$: Describe the appearance of:
a: a mixture of iron and sulfur.
b: the iron sulfide.
${A_2}$: Could you remove the iron from the iron sulfide using a magnet? Explain your answer.
Air is a mixture
When you mix iron and sulfur together, you are making a mixture of two elements.
Mixtures can also contain compounds. For example, air is a mixture of several different elements and compounds. Air contains nitrogen, oxygen, carbon dioxide, water vapour and small quantities of some other gases.
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Particle diagrams of some of the gases in air.
Questions
Look at the particle diagrams of the gases in air to answer these questions.
1) List the formulae of the four different gases shown in the diagrams.
2) Which of the gases in air are elements? Explain how you can tell.
3) Which of the gases in air are compounds? Explain how you can tell.
4) Explain why air is a mixture, not a compound.