Why Can You Get the Salt Back Out?

Step 1 of 5

Mixing is not joining.

Stir salt into water and the salt is still salt, just broken into pieces too small to see. Nothing new was made, so nothing has to be unmade.

Step 2 of 5

How you separate it depends on how it differs.

Pick the difference and there is a tool for it: size for a sieve, floating for a filter, and boiling point for a warm windowsill.

Step 3 of 5

Evaporating leaves the solid behind.

Water can escape into the air as a gas. Salt cannot, so as the water leaves, the salt is left sitting there in the dish.

Step 4 of 5

A magnet is just another difference to use.

Stir iron filings into sand and no chemistry has happened. Run a magnet over the top and the iron leaps out, still iron.

Step 5 of 5

Most things you meet are mixtures.

Air, seawater, milk, soil and steel are all mixtures. Genuinely pure substances are rare enough that making one is a job in itself.

Seawater holds so much dissolved salt that if you spread the salt from all the oceans over the land, it would bury it about 150 metres deep.