Mixtures and separation

One mixture of sand, iron filings and salt, in two equal portions. The steps show what happens, not exact amounts or times: the amounts are illustrative, the waits are shortened, and the grains are drawn far larger than real ones.

In a real filter some salt solution stays in the wet paper and sand, so a little salt is lost. The hotplate’s glow shows that it is on, not a measured temperature.

The close-up in the card is schematic: white circles for water particles and small purple squares for the dissolved salt’s particles, which are really ions. Real grains of sand and iron filings are millions of times larger than these particles.

The colours only tell things apart: real salt is white, and water and salt solution are colourless, although the water is drawn pale blue so that you can see it.

Never taste laboratory samples. Real heating needs a teacher-approved safety procedure: heat gently, and stop when the first crystals appear, because the last of the water can spit hot salt. The rest evaporates by itself.

With reduced motion, each step finishes at once.