Universal Solvent Secrets
Why water dissolves salts and gases
What this lesson covers
Why it matters
Stir salt into oil and it just sits there. Stir it into water and it vanishes. Water dissolves so many things because its molecules are polar — tiny magnets that pull charged particles apart.
Predict first
Why does water dissolve salt while oil does not?
'Like dissolves like.' Polar water dissolves ionic and polar substances (salt, sugar, copper sulphate). Non-polar substances (oil, wax, petrol) don't dissolve in water — but dissolve in non-polar solvents.
- Water is polar, so it pulls apart the charged ions in salt; oil is non-polar — correct
- Water is thinner and runnier than oil
- Salt is simply lighter than oil
What you do
Sort each substance: does it dissolve in water, or not?
Check yourself
Why is water called the 'universal solvent'?
Water dissolves more substances than any other common liquid — but not non-polar things like oil, so not literally everything.
Oil would best dissolve in…
Like dissolves like — non-polar oil dissolves in non-polar solvents, not in polar water.
- Its polarity lets it dissolve a very wide range of substances — correct
- It can dissolve absolutely everything
- It is the only liquid that dissolves things
- a non-polar solvent like petrol — correct
- water, given enough stirring
- salt water