PAG 5 - Synthesis of an Organic Liquid (4.2.3a)

Question 1

Label all the Quickfit Apparatus

Answer 1

1. Pear-shaped flask (round-bottom flasks also used)
2. Still-head
3. (Liebig) Condenser
4. (Screwcap) Adapter
5. Receiver Adapter
6. Inlet tube (no one really needs to know that)
7. Dropping Funnel
8. Stopper
9. Thermometer

Question 2

What equipment is needed for a reflux and how is it set-up?

Answer 2

Equipment

• Round-bottom/pear flask
• Liebig condenser (vertically positioned)
• Rubber tubing
• Clamp/stand
• Heat source
  
  • Heating mantle if substance is volatile e.g. alcohol

Set-up

• Use anti-bumping granules to stop violent flash boiling
• Open top - otherwise pressure builds up and the bung shoots off
• Cold water in at the bottom
  
  • Water out the top
• Grease the joints to provide a good water-tight seal

Question 3

What equipment is needed to set up distillation?

Answer 3

Equipment

• Round-bottom/pear flask
• Condenser
• Rubber tubing (used as a water inlet, water enters at lowest point of condenser)
• Heat source
• Clamp & stand
• Screw-cap adaptor
• Receiver adaptor
• Still head (connects flask to condenser)
• Thermometer (blocks top of still-head by sitting on screw cap)

Question 4

What is a separating funnel used for?

Answer 4

• When preparing organic liquids, water may be obtained with the product
  
  • You will see 2 liquid layers (one aq layer and one organic)
  • Denser liquid will always sink to bottom (usually water)

Question 5

If there are 2 layers in your liquid when purifying organic products, how do you know which is the organic one?

Answer 5

Keep adding water, the layer that gets bigger is the aq layer

Question 6

What is the method for purifying an organic product?

(1st stage)

Answer 6

Separate, dry and distil

Separate

1. Ensure tap of separating funnel is closed
2. Pour mixture of liquids into funnel, add a stopper, invert to mix and allow layers to settle
3. Add water and check which is the aq layer
4. Place a conical flask underneath and open the tap until the whole lower layer has left the funnel

Question 7

What is the method for purifying an organic product?

(2nd stage)

Answer 7

Dry

There may be some water in the organic product so add a drying agent

CaCl₂ - drying hydrocarbons

CaSO₄/MgSO₄ - general drying

1. Add organic layer to conical flask
2. Add drying agent and swirl, place stopper on flask and leave for 10 minutes
3. If the solid is in a clump, it means there is still water, add more drying agent until the solid is dispersed
4. Decant the liquid from the solid into another flask, if the liquid is dry it is clear

Question 8

When preparing acids there may be acid impurities, how do you get rid of them?

Answer 8

• Add sodium carbonate to release CO_2(g) (in the separating funnel)
• Release the tap slowly whilst the funnel is inverted to release gas pressure
• Finally, when no more gas is released, remove the aq sodium carbonate layer

Question 9

What occurs if there are still some organic impurities after separating and drying?

Answer 9

• Redistil as the organic impurities may have similar boiling points
• Only collect the fraction distilling at the temperature of your desired product