preparation and separation techniques
- 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