Mixing, dissolving and changing

For grown-ups: this lesson in words

Years 5 and 6 · Science

Mixing, dissolving and changing: I can tell what dissolves, separate mixtures, and spot changes that make new materials.

1. Here is a sugar cube. Sugar is a solid.

   The sugar is stirred into some water with a spoon.

   Soon we cannot see the sugar. It has dissolved: it has broken up into bits too tiny to see.

   The sugar is still there, mixed all through the water. Together they make a solution.

   Picture: A sequence called Dissolving with 3 stages, in order: Sugar cube, then Stirred into water (a picture of a spoon), then Sugar solution (a picture of a glass jar).

2. Some solids dissolve in water, and some do not.

   Sugar and salt dissolve. They seem to disappear and make a clear solution.

   Soil does not dissolve. The bits of soil stay in the water, and we can still see them.

   Pebbles and rice do not dissolve either. They stay as pebbles and grains of rice.

   Picture: Sorting into 2 groups: Dissolves in water, Does not dissolve. Dissolves in water: Sugar cube (cube), Spoonful of salt (spoon). Does not dissolve: Soil (pile of soil), Pebbles (rock), Rice (bowl of rice).

3. Your turn: Mei stirs a little of each one into a glass of water. Which one dissolves?

   Choose one:

   • Pebbles
   • Salt
   • Rice

   Answer

   The answer: Salt

   Salt dissolves. It breaks up into bits too tiny to see and makes a solution.

Words to know

dissolve:

When a solid mixes into a liquid and breaks into bits too tiny to see.

solution:

A liquid with a solid dissolved in it, like salt water.

evaporate:

When a liquid turns into a gas and goes into the air.

filter:

To pour a mixture through paper with tiny holes that catches solid bits.

reversible:

A change that can be undone, like melting ice.

irreversible:

A change that makes a new material and cannot be undone, like burning.