Mixtures and Separation Techniques – JSS1 Intermediate Science Lesson Note (First Term)

WHAT IS A MIXTURE?

In our last lesson, we looked at pure substances. But in the real world, most things are mixed together.

Definition of a Mixture

A mixture is what you get when you put two or more substances together, but they do not chemically join. Because they are just “hanging out” together, we can usually separate them back into their original forms.

Examples of Mixtures:

• Garri and Sugar: You can still see the grains of sugar and garri.
• Saltwater: Even though the salt disappears, it is still there (you can taste it!).
• Air: A mixture of different gases like oxygen and nitrogen.

Why do we separate mixtures?

1. To remove dirt or impurities (like picking stones out of beans).
2. To get a useful substance (like getting salt from seawater).
3. To purify the water we drink.

SEPARATION TECHNIQUE 1 – DECANTATION

Decantation is the simplest way to separate a liquid from a heavy solid that does not dissolve.

How it works:

If you have a mixture of sand and water, you let it sit still for a while. The heavy sand will settle at the bottom (this is called sediment). You then carefully pour off the clear water into another cup without disturbing the sand at the bottom.

Where do we use this?

• At home, when you wash rice or beans, you pour off the dirty water carefully while the rice stays at the bottom. This is decantation!

The Downside: It is not 100% perfect. Sometimes a little bit of sand gets into the second cup, or you leave some water behind.

SEPARATION TECHNIQUE 2 – FILTRATION

Filtration is like a “super version” of decantation. We use it when we want to be very sure that no solid particles get into our liquid.

How it works:

We use a Filter Paper (which acts like a very fine sieve with tiny holes).

1. We fold the filter paper into a cone and put it in a funnel.
2. We pour the mixture (like muddy water) into it.
3. The liquid passes through the tiny holes and drops into a flask below. This clean liquid is called the Filtrate.
4. The solid dirt stays trapped on the paper. This is called the Residue.

Where do we use this?

• Using a “sieve” to get the chaff out of pap (Akamu/Ogi).
• Water treatment plants use big filters to make our tap water clean.

SEPARATION TECHNIQUE 3 – EVAPORATION

What if the solid has completely disappeared into the liquid? For example, salt in water. You cannot use a sieve or decantation because the salt is too tiny!

How it works:

We use heat! Since water turns into steam (gas) when heated, but salt does not, we can separate them using the boiling point.

1. Put the saltwater in an evaporating dish.
2. Heat it over a Bunsen burner.
3. The water boils away into the air as steam.
4. The white salt crystals are left behind in the dish.

Where do we use this?

• To get sea salt from the ocean.
• Drying clothes in the sun (the water evaporates, leaving the dry cloth).

Summary Table

Class Activity

1. If you accidentally drop your ring into a bowl of muddy water, which method would you use to get it back quickly?
2. Why can’t we use filtration to get salt out of water?
3. What is the name of the liquid that passes through the filter paper?