Separating mixtures by physical properties: an interactive model where a mixture of sand, salt and iron filings is separated by a magnet, filtration and evaporation, and each component's percentage composition by mass is calculated.

To separate a mixture you make nothing new — you exploit its differences

Stir sand, salt and iron filings together and they are still three separate substances, each keeping its own physical properties. Pull them apart one property at a time, weigh what you recover, and the percentage composition of the mixture falls out. Pick a sample, then step the separation forward to run the magnet, the filter and the evaporating basin.