Chapter 3- Separation and purification

Question 1

How does a mixture differ from a pure substance?

Answer 1

Mixtures are made of 2 or more substances not chemically combined.

Pure substances are made up of one single element or compound, unmixed with any other substances

Question 2

How do we separate solids from liquids?

Answer 2

Filtration: separate insoluble solid particles from liquids

Evaporation to dryness: Obtain soluble solid from solution by heating till liquid boils off

Crystallisation: Evaporation to dryness but for pure solid samples (Filtration + Evaporation to dryness)

Question 3

How do we separate solids?

Answer 3

Using a suitable solvent: Only 1 solid is soluble in used solvent

Sublimation: Where only 1 solid sublimes

Using a magnet

Question 4

How do we separate liquids from solutions?

Answer 4

Simple distillation: Separate pure solvent from solution (boiling a liquid and condensing the vapour)

Question 5

How do we separate immiscible liquids?

Answer 5

Using a separating funnel

Question 6

How do we separate miscible liquids?

Answer 6

Fractional distillation (simple distillation + fractioning column)
- Used to obtain pure gases from air and separate petroleum into useful fractions

Question 7

How do we separate 2 or more components that dissolved in the same solvent?

Answer 7

Paper chromatography. Use locating agent for colourless substances.

Question 8

How do you calculate Rf value?

Answer 8

Distance travelled by substance/Distance travelled by solvent

The value should usually be below 1

Question 9

What effects does purity have on solids and liquids?

Answer 9

Pure substances have fixed melting and boiling points

Impurities lower melting point and increase boiling point. These points also have a range instead of a specific temperature