How can we identify what is in a mixture and separate useful materials from one another?
By the end of this chapter, you should be able to:
Start with something you already know.
Imagine helping at home to prepare food. You put water into a bowl and add gari. Later, you prepare a drink and add sugar to water. At the market, a trader separates stones from beans. Someone filtering water removes unwanted particles.
What do all these activities have in common?
Build the ideas step by step.
A mixture is formed when two or more substances are combined physically without forming a new substance. The materials in a mixture retain their individual properties.
Sand remains sand and water remains water. They have simply been brought together.
A homogeneous mixture has a uniform composition throughout. A heterogeneous mixture is not uniform throughout and its components can often be distinguished.
Example: salt solution or sugar solution.
Example: oil and water or sand and water.
The substance that dissolves is the solute. The substance that dissolves the solute is the solvent. Together they form a solution.
A suspension contains relatively large particles dispersed in a fluid. The particles may settle when the mixture is left undisturbed.
Example: groundnut paste and water.
Leave the mixture undisturbed and some particles may settle.
A colloid contains particles larger than those in a true solution but small enough not to settle easily like suspension particles.
Colloidal particles can scatter light. This is called the colloidal effect (Tyndall effect).
| Feature | Colloid | Suspension |
|---|---|---|
| Particles | Intermediate size | Relatively large |
| Settle easily? | Usually no | Often yes |
| Example | Milk | Groundnut paste + water |
Mixtures can often be separated because their components have different physical properties.
Be the scientist.
Materials: 3 transparent cups, water, salt, sand, oil and a spoon.
Mix sand and gravel. Place the mixture into a sieve and shake it gently over a bowl.
Conclusion: sieving works because the particles have different sizes.
Use a clean cloth or filter paper, funnel, container, sand and water. Pour the mixture through the filter. Observe what passes through and what remains.
Reason, don't just recall.
A learner says: “If I cannot see a substance in a mixture, that substance is no longer there.”
Find science where you live.
Removing unwanted materials from harvested crops.
Working with mixtures during food and drink preparation.
Screening and separating materials according to particle size.
Removing unwanted particles from water.
Using separation processes when processing raw materials.
Find three examples of mixtures in a home, farm, market, school, workshop or food-processing activity.
Build your science vocabulary.
Test yourself. Questions increase in difficulty.
Design your own separation station.
Work in groups. Given a safe mixture, identify its components, identify different physical properties, choose a separation method, perform it, record observations and explain why it worked.
Apply what you have learned.
Design an investigation to separate sand and water. Include materials, procedure, observation, method, property used and conclusion.
“All mixtures can be separated using the same method.” Do you agree? Use at least three mixtures to support your answer.
What should stay in your mind?
Mixtures are made when substances are physically combined, and their different physical properties can help us identify, investigate and separate their components.