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You have tested materials in water and seen that some dissolve and some do not. Mia stirs a spoonful of salt into a glass of water. The white grains vanish and the water looks clear.
What happened to the salt?
Dissolving & Solutions
Understand that some materials dissolve in liquid to form a solution, and describe how to recover a substance from a solution by evaporation
What a learner can do afterwards
- Explain that dissolving means a solid mixes completely into a liquid to form a solution
- Describe how to recover a dissolved substance by evaporating the liquid
- Distinguish between a mixture (can see separate parts) and a solution (looks clear, fully dissolved)
1 · Read
You already know that dissolving mixes a solid completely into a liquid. Look closer now at what that mixture becomes. When sugar dissolves in tea, you cannot see the sugar anymore, but it is still there. The tea stays clear, with no solid bits floating in it. This kind of mix is called a solution.
Try it together
Mia stirs a spoonful of salt into a glass of water. At first she sees small white grains. After stirring, the grains vanish and the water looks clear. Mia has made a salt solution.
Good to know
A mixture with visible bits, like sand in water, is not a solution. A true solution looks clear and smooth all the way through, even though something is dissolved inside it.
You can get the dissolved solid back. Leave the solution somewhere warm and let the liquid evaporate. As the liquid turns to vapor and drifts away, the solid stays behind. Evaporate the water from salty water, and solid salt is left in the container.
Not every mix is a solution. If you can still see bits, like sand sitting at the bottom of a glass, the solid never dissolved and you have a mixture, not a solution. A filter can catch those undissolved bits, but a dissolved solid slips right through the filter with the water. To get a dissolved solid back, evaporate the liquid instead.
Dissolving mixes a solid completely into a liquid to make a clear solution, and evaporating the liquid brings the dissolved solid back.
The rewritten readings were written for this dataset. Readings 'Where did the sugar go?' and 'Getting salt back from salty water' are original to this dataset.
2 · Watch
3 · Play
Take it off screen
Print a worksheetA4 with an answer key page for grown-ups. No screen, no internet.
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
Then practise
24 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.