Purifying Organic Compounds

Question 1

What are the 6 techniques used to purify compounds?

Answer 1

Separation + Solvent extraction
Drying Agents
Washing
Recrystallisation
Distillation + Redistillation
Testing Purity

Question 2

Describe how SEPARATION works?

Answer 2

Used if an organic product is insoluble in water
Used to remove any impurities that dissolve in water (e.g. salts)
The organic layer and aqueous layer DO NOT MIX
2 distinct layers forms
Organic layer is less dense
So the organic layer should float on the top
Then open stopper on separating funnel + run off the aq layer + collect product

Question 3

Meaning of immiscible?

Answer 3

The two liquids do not mix

Question 4

Describe how solvent extraction works?

Answer 4

This is used if products and impurities dissolve together –> Vigorously shake impure product with an immiscible solvent
They temporarily mix
Product needs to be more soluble in immiscible solvent than in original solvent (from separation)
The product dissolves in the added solvent + separates from impure solution
The solvent containing product can be run off using a separating funnel

Question 5

Describe how distillation works?

Answer 5

It separates liquids with different boiling points
Gently heat mixture in distillation apparatus
Substances evaporate out of mixture by different boiling points
Thermometer placed at neck of condenser –> shows boiling point

Question 6

Describe how redistillation works?

Answer 6

Mixtures that contain volatile liquids can be purified this way
If product and its impurities have different boiling points
Use same apparatus as distillation but this time heat an impure product
When the liquid that is the product you want boils - the thermometer shows its bp, place a flask at the end of the condenser, look at the thermometer and as soon as the temperature changes - change flask

Question 7

Explain how washing works?

Answer 7

The product of the reaction can be contaminated with unreacted reagents or side products - these can be removed by washing the product
e.g. Excess sodium hydrogencarbonate solution removes acid to give CO2 gas, H2O and salt
This leaves an aqueous solution of the excess aq sodium hydrogencarbonate + salt + water
Remove the organic product using a separating funnel assuming it is insoluble in the aqueous layer