Purification Methods

Question 1

What equipment is required for a simple distillation?

Answer 1

1. Round bottom/pear shaped flask
2. Thermometer
3. Liebig Condenser
4. Conical flask

Question 2

What are anti bumping granules for?

Answer 2

To ensure that when heating a solution doesn’t boil to aggressively.

Question 3

How would you carry out a simple distillation?

Answer 3

1. Put the mixture in a pear shaped flask with anti-bumping granules.
2. Place the thermometer so the bottom is level with the side arm to the condenser.
3. Heat the mixture until the boils gently
4. When the mixture is 2oC below the boiling point of the desired product place the collection beaker in place.
5. Stop heating if the temperature rises above the boiling point of the desired product

Question 4

How would you change the method if you wanted to collect multiple fractions?

Answer 4

Just change the beaker at the appropriate temperature ranges

Question 5

Describe how to set up a TLC (Thin Layer Chromatography) or Paper Chromatography

Answer 5

1. Spot your samples 1cm from the base of the paper on a pencil line
2. Suspend in a beaker with solvent in the base and cover with a watch glass
3. Remove from the solvent when it reaches close to the top
4. Use iodine, ninhydrine, or UV light to detect and record the spots
5. Calculate the Rf values and compare to known values with the same solvent

Question 6

How could you determine the purity using chromatography?

Answer 6

Compare the pure samples and detect no additional spots

Question 7

How could you purify a crude organic solid?

Answer 7

Recrystallisation

Question 8

Describe how you recrystallise a solid product?

Answer 8

1. Use a solvent in which your product is very soluble so you can use the smallest amount possible (otherwise your yield will decrease)
2. Dissolve in the minimum quantity of hot solvent
3. Filter to remove impurities with a preheated filter funnel and flask (to prevent crystallisation).
4. Cool and collect the crystals by vacuum filtration
5. Dry in the oven

Question 9

Describe how to set up the vacuum filter

Answer 9

1. Connect to a vacuum pump via the side arm
2. Dampen a piece of filter paper and place in the buchner funnel
3. Carefully pour the mixture through with the vacuum pump on
4. Disconnect from the pump before turning the pump off to avoid ‘suck back’.