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Dissolving Materials in Water
Objectives
- To understand that certain materials will dissolve when mixed with water.
- To recognise that certain materials do not dissolve in water - they are insoluble.
- To discover that some materials appear to dissolve, but simply mix with the water.
Resources
Cambridge Primary Science Book 3 | Salt crystals | Water | Plastic tray
Today's Lesson
Main Activity
Watch the video Why is Sea Water Salty?, watch as many times as you need to. Think about the process that is explained.
Discuss the difference between fresh water lakes and rivers and the salt water of the sea with your child. Ask your them why they think the sea is salty. The answer may be known already.
Talk about the amount of salt in the earth as rock salt and how this dissolves in rain, which flows into rivers and eventually finds its way into some lakes, but ultimately, the sea. When the water from the sea evaporates to create clouds in the sky, the salt does not evaporate with the water. It remains behind in the dissolved state.
Take a tea-spoon of salt and ask your child to dissolve it in a ¼ cup of water. Once the salt has ‘disappeared’ completely, ask them where they think the salt is now. It may not be visible but ask them to dip a finger in the liquid and to taste it. The salt is still very much there - it has dissolved, not disappeared. Salt is soluble in water. Explain this is called dissolving.
Next, place the liquid, from the experiment on a plastic tray and put it in the sun, or in a warm, dry area.
Read Cambridge Primary Science Book 3 pages 45 and 46 - Dissolving.
Discuss that they have completed the same experiment with sugar. Read page 46 and answer the questions.
After you have finished the questions, the water may have evaporated, leaving salt crystals behind. If not, leave it for longer. What has happened to the water? It has evaporated due to heat. What is left? Ask your child to create a series of diagrams to write up this experiment. They will also need to list the equipment required.
We will investigate this further in the next lesson.