Purifying organic compounds Flashcards
When can you use separation?
If an organic product is insoluble in water, separation can be used to remove any impurities that do dissolve in water.
How does separation work?
The organic layer and the aqueous layer don’t mix so you can then open the tap and run each layer off into a separate container
Out of the organic and aqueous layer, which one is usually less dense?
The organic layer so it will float on top of the aqueous layer and the aqueous layer can be tapped off
What does solvent extraction involve?
Vigorously shaking the impure product with an immiscible solvent so they temporally mix. The product will dissolve in the added solvent and separate from the solution with the impurities and therefore the solvent containing the organic product can be run off using a separating funnel
What is a drying agent and why is it used?
Drying agents bind to any water present to become hydrated
If separation is used to purify a product, the organic layer will end up containing trace amounts of water
What are some examples of drying agents?
MgSO4
CaCl2
When do you know all of the water has been removed by the drying agent?
When you can swirl the mixture and it looks like a snow globe as the solid drying agent can be removed
Why is washing done?
Remove any unreacted reactants or unwanted side products that might have contaminated the produce of a reaction
What is distillation?
Separating liquids with different boiling points as the substances will evaporate out of the mixture in order of increasing boiling points
Why is a thermometer used in distillation?
Placed at the neck of the condenser to show the boiling point of the substance that is evaporating at any given time
What can you do if the produce of a reaction has a lower boiling point than the starting materials?
The reaction mixture can be heated in distillation apparatus so that the product evaporates from the reaction mixture as it forms
When can you use redistillation?
If a product and it’s impurities have different boiling points
What is the process of recrystallisation?
1) add a very hot solvent to the impure solid until it just dissolves, giving a saturated solution of the impure product
2) Leave the solution to cool down slowly and crystals will start to form
3) The impurities will stay in the solution
4) filter out the crystals and wash them with an ice-cold solvent, then dry them
How can you test purity?
1) Pack a small sample of the solid into a glass capillary tube and place it inside the heating element
2) increase the temperature until the sample turns from solid to liquid
3) Measure a melting range - from when they start to melt to when they’re fully melted
4) Then look up the melting point of a substance in data books and compare it to your measurements
What will impurities in the sample do to the melting point and melting range?
Lower the melting point
Increase the melting range
