chemists often have to carry out reactions and then separate the products from the initial reactants

when deciding which techniques to use the following must be taken into consideration

liquid or solid reagents

how long the reaction takes

amount of heat required and volatility of liquid reagents

preparation and separation techniques

• reflux

• distillation

• fractional distillation

• drying

• solvent extraction

• precipitation

• crystallisation

• filtration

• chromatography

apparatus

• condenser

• round bottomed flask

• heating mantle

• lab jack

• anti bumping granules

reflux

• allow organic substances with low boiling point to be heated for long periods without loss due to evaporation

• many organic reactions require heating for long periods in order to maximise the yeild

• the reaction mixture is places in a flask and a lie big condenser is attached

• the condenser cools the evaporating vapours returning them to the flask

precautions

• use a heating mantle for higher temperatures than boiling water

• use anti bumping granules to prevent formation of large gas bubbles in the reaction mixture

• water flow goes in at the bottom of the condenser and out at the top

distillation

• used to separate compounds out from a mixture of liquids

• relies on differences in boiling points

• liquids are heated until the vapour pressure equals that of atmospheric pressure where the compound starts to boil

• components of lower boiling point boil first and are collected first

fractional distillation

• used to separate several liquids from a mixture

solvent extraction

• a way of separating compounds based on their differing solubility in 2 immiscible liquids eg petroleum spirit and water

• a way of purifying a a substance eg chlorophyll extraction

• chlorophyll is more soluble in petroleum spirit than water.when it is extracted from pant leaves an acetone/water mixture is used