Required Practical 10 Flashcards
What is reflux?
The continuous boiling and condensing of a reaction mixture.
Why is reflux used?
It allows an organic reaction mixture to be heated without losing any reactants or products.
What method is used to purify an organic liquid?
Separation.
How does separation work?
The aqueous solution and the organic product have different densities and are immiscible.
This causes the liquids to separate into the aqueous layer at the bottom and the organic product at the top.
What are the steps for separation?
1) Put the distillate of the impure product into a separating funnel.
2) Wash the product in sodium hydrogencarbonate solution, shaking and releasing pressure from the CO₂ produced.
3) Allow the layers to separate in the funnel and then run and discard the aqueous layer.
4) Run the organic layer into a clean, dry conical flask and add a drying agent to remove water.
Why is sodium hydrogencarbonate solution added when separating liquids?
To remove acidic impurities by neutralisation.
Why is a drying agent used?
To ensure that there isn’t any water left.
What compounds can be used as drying agents?
MgSO₄ or CaCl₂
How would a solid organic product be purified?
Recrystallisation.
What are the steps for recrystalisation?
1) Dissolve crude product in hot water of a minimum volume.
2) Filter to remove insoluble impurities.
3) Cool to recrystallise.
4) Filter under reduced pressure with Buchner apparatus.
5) Wash with cold solvent and dry.
Why is a minimum amount of water used for recrystallisation?
To obtain a saturated solution which enables the maximum amount of crystals to be produced on cooling.
Why do the impurities not form crystals?
They are only present in small quantities so the solution is not saturated and will not form crystals.
Why are the crystals washed?
To remove soluble impurities.
Why are the crystals dried?
To remove the excess water which would affect the percentage yield.
What can cause a loss of yield in the recrystallisation process?
Crystals lost when filtering or washing.
Some product stays in solution after recrystallisation.
Other side reactions may occur.
