Elements, Compounds and Mixtures

Question 1

How to classify something as an element, compound or mixture

Answer 1

Element - One type of atom
Compound - Two or more elements chemically bonded
Mixture - Two or more substances not chemically bonded

Question 2

What is the difference between the boiling/melting point of a pure substance and a mixture?

Answer 2

Pure - set boiling/melting point (e.g. pure water 100 degrees)
Mixture - range of temp (e.g. water 97-102 degrees)

Question 3

Describe experimental techniques for simple distillation

Answer 3

Separate liquid from solution
Solution is boiled
Solvent evaporates and condenses in Liebig condenser
Collected in beaker
Solute left behind

Question 4

Describe experimental techniques for fractional distillation

Answer 4

Separate mixture of different liquids with different bp
mixture is boiled to lowest bp
that evaporates and condenses and is collected

Question 5

Describe experimental techniques for filtration

Answer 5

Separate insoluble solid from a liquid
Funnel and filter paper
collect solid in filter paper
collect liquid in beaker

Question 6

Describe experimental techniques for crystallisation

Answer 6

Obtain salt from salt solution
Slowly heat in evap. basin
until 1/3 has evap.
Leave to cool and crystallise
Filter to remove crystals
Dry in warm oven

Question 7

Describe experimental techniques for paper chromatography

Answer 7

Separate dyes
Pencil line
Dots
Solvent below pencil line
wait a few mins
solvent front
calculate Rf (distance dye/solvent front)

Question 8

How can chromatography give info on composition of mixture

Answer 8

Dyes that travel the same height, are the same
Separates colours

Question 9

How can Rf values identify components of a mixture

Answer 9

More soluble = higher Rf
Rf = 0 = insoluble