Grow salt crystals in a KS3 evaporation and crystallisation virtual lab. Includes a printable pupil worksheet and answer sheet.

Which will produce larger salt crystals: a frozen slide or a warm slide? Pupils make a prediction, prepare a saturated salt solution and gently heat it until crystals appear at the edge of the evaporating basin. They then place a drop on each slide and use a virtual light microscope to see whether the evidence supports their prediction.

What pupils investigate

• Saturation. Measure the water, add salt and stir until no more salt dissolves.
• Evaporation. Transfer the clear solution to an evaporating basin. Watch for the first crystals at the edge and decide when to stop heating.
• Crystallisation. Compare the size, number and shape of the crystals on both slides. In the simulation, the frozen slide produces many small crystals, while the warm slide produces fewer, larger crystals.
• Fair comparisons. Focus the microscope on each slide using the same magnification. Explain why changing the magnification could make one sample appear to have larger crystals.

What’s included

The interactive online experiment comes with a one-page printable worksheet and a completed answer sheet. Pupils record their prediction, compare their microscope observations in a table, put six practical steps in order and explain what happens to the water and the dissolved salt.

Where it fits in your scheme of work

Use this alongside the White Rose Science Year 7 lesson on Crystallisation and evaporation in the separation techniques unit. For Exploring Science, including Exploring Science International, and AQA Activate, use it when teaching mixtures and how to recover a dissolved solid from a solution.

For a whole-class lesson, project the lab and pause before revealing the microscope views. Pupils can sketch what they expect to see, then check their predictions against the crystals on each slide.