Methods of Purification

Question 1

Filtration

Answer 1

used to separate a mixture of liquid and an insoluble solid

insoluble solid is collected as the residue while the liquid is collected as the filtrate

Question 2

Evaporation

Answer 2

used to evaporate off the solvent from a solution to obtain the dissolved substance
only applicable for substances that do not decompose upon heating

Question 3

Crystallisation

Answer 3

used to recover a dissolved substance from its solution

useful for substances that decompose upon heating

carried out by heating a solution until it is saturated, saturated is left to cool allowing the substance to crystallise

when the solution is heated, the solubility of the solution increases, and the volume of the solution decreases due to boiling/evaporation
when the solution cools, the solubility of the solution decreases, hence crystals forms

Question 4

Sublimation

Answer 4

used to obtain a solid that sublimes from a solid mixture (e.g. iodine and naphthalene)

Question 5

Distillation

Answer 5

used to separate a liquid from a mixture

substances in the mixture must have large differences in boiling points for the pure liquid

Question 6

Fractional distillation

Answer 6

used to separate a mixture that contains two or more liquids that have relatively close boiling points

the vapour produced is a mixture of substances

fractionating column aids in separating the vapour into individual components, which allow for the collection of pure substances

Question 7

Separating Funnel

Answer 7

used to separate a mixture of liquids that have different densities

Question 8

Paper chromatography

Answer 8

used in the separation of small quantities of mixtures
the mixture is separated based on the difference in solubility of its components in a particular solvent
a locating agent is used to expose colourless spots in a chromatogram

Rf value = distance moved by component from starting line/distance moved by solvent from starting line