Separating Liquids

Why it matters

Pour cooking oil into water and it just floats on top in a clear layer, refusing to mix. Stir salt into water, though, and it vanishes completely. Two liquids, two very different problems to solve.

Predict first

Oil and water are poured together and settle into two separate layers that will not mix. What is the neatest way to separate them?

Liquids that do not mix (immiscible), like oil and water, form layers and are separated in a separating funnel by their density. Liquids that do mix or are dissolved, like salt in water, are separated by distillation.

• Boil the mixture and collect the steam
• Use a separating funnel and run off the lower layer — correct
• Pour it through filter paper
• Bring a magnet near it

What you do

Pick the right tool for each pair: a SEPARATING FUNNEL (they do not mix) or DISTILLATION (dissolved or mixed).

Check yourself

Two liquids that do not mix with each other are said to be:

Liquids that do not mix and instead form separate layers, like oil and water, are called immiscible liquids.

A separating funnel separates oil and water on the basis of their difference in:

Oil is less dense than water, so it floats on top. In a separating funnel the denser lower layer is run off first, separating the two.

To get pure water from sea water (which has dissolved salt), you would use:

The salt is dissolved, so distillation is used: the water is boiled to vapour, then the vapour is cooled and condensed back to pure water, leaving the salt behind.

• Immiscible — correct
• Miscible
• Soluble
• Magnetic
• Density, so the layers can be run off one at a time — correct
• Colour, so the funnel picks the brighter one
• Magnetism
• Taste
• Distillation: boil the water, then condense the vapour — correct
• A separating funnel to pour off a layer
• A magnet
• Filter paper