Science notes, unit 8

Mixture

Textbook Science Year 2 (DLP), pages 87–100

What this chapter covers

You know that a mixture has two or more materials mixed together (8.1.1)
You can separate a mixture by hand-picking, sieving, using a magnet, floatation and filtration (8.1.2)
You can say which materials dissolve in water and which do not (8.1.3)
You know that materials dissolve more quickly in hot water and when stirred (8.1.4)
You know that small pieces dissolve more quickly than big pieces (8.1.5)

Muruku and nuts, flour and raisins, sand and paper clips. When two or more things are together, we have a mixture. In this unit you will learn how to separate mixtures and how things dissolve in water.

8.1Mixtures

What is a mixture?

Mixture: two or more materials that are mixed together.

We can separate the materials in a mixture. We choose a method that suits the materials.

Ways to separate a mixture

Method	Use it to separate	Example
Hand-picking	Two big materials with different shapes	Muruku and nuts
Sieving	Fine materials from large materials	Flour and raisins
Magnet	Materials that a magnet attracts	Paper clips and sand
Floatation	Materials that float from materials that sink	Wood bits and sand
Filtration	Solid from liquid	Hibiscus petals and coloured water

Hand-picking

Hands picking nuts and muruku into separate plates — Nuts and muruku are big and have different shapes. We pick them by hand.

Sieving

A sieve over a bowl: fine flour falls through and raisins stay on the sieve — The fine flour goes through the sieve. The raisins stay on top.

Using a magnet

A magnet picking up paper clips from sand in three steps — The magnet attracts the paper clips. The sand stays behind.

Careful! A magnet only attracts some metals, such as iron. It cannot pick up sand, wood or plastic.

Floatation

Water poured into a fish bowl, then wood bits floating on top are lifted out — Pour in water and stir. The wood bits float. The sand sinks.

Filtration

A filter paper is folded into a cone and put into a funnel above a conical flask — Fold the filter paper and put it in the funnel.

Pink liquid is poured through a filter paper in a funnel into a conical flask — The pieces of petals stay on the filter paper. The coloured liquid goes into the conical flask.

Which method?

Green beans and flour: the beans are big and the flour is fine. Use sieving.

How do we separate iron paper clips from sand?

Show answerHide answer

Use a magnet.

8.2Dissolving

Dissolve or not?

Some materials dissolve in water. We cannot see them after we stir. Some materials do not dissolve. We can still see them.

Sugar and corn kernels added to water; after stirring only the corn kernels can be seen — The sugar dissolves. The corn kernels do not dissolve.

Dissolves in water	Does not dissolve in water
Sugar, salt	Corn kernels, green beans, rice

How can we dissolve things more quickly?

Use hot water. Sugar dissolves more quickly in hot water than in cold water.
Stir. Stirred sugar dissolves more quickly.
Use small pieces. Coarse sugar dissolves more quickly than a sugar cube.

Beaker A with cold water and beaker B with hot water; one teaspoon of sugar is added to each — Cold water in A, hot water in B. Sugar dissolves more quickly in B.

Sugar is added to two beakers and only beaker B is stirred — Only beaker B is stirred. The sugar in B dissolves more quickly.

Remember: hot water, stir, small pieces.

Name one way to make sugar cubes dissolve more quickly.

Show answerHide answer

Stir them, use hot water, or crush them into small pieces.

Figures: Science Year 2 (DLP) textbook, pp. 89 to 94 and 96 to 99, cropped for revision.

Summary

Idea	Remember
Mixture	Two or more materials mixed together
Separating	Hand-picking, sieving, magnet, floatation, filtration
Dissolve	Sugar and salt dissolve. Rice and beans do not.
Dissolve more quickly	Hot water, stirring, small pieces