Module 6: Organic Synthesis (6.2.5)

Question 1

Separation of a Solid from Liquid

Answer 1

1. Connect 1 end of pressure tubing to vacuum outlet/pump and other end to rubber tubing on Buchner flask.
2. Fit Buchner funnel into flask using rubber bung.
3. Switch on pump or tap to which filter pump is attached.
4. Place filter paper inside Buchner funnel and wet with same solvent used to prepare the solid.
5. Pour reaction mixture from a beaker slowly down the funnel, aiming for the centre.
6. Rinse beaker with solvent so all crystals enter funnel.
7. Rinse crystals in funnel with more solvent and let them dry.

Question 2

Recrystallization

Answer 2

1. Pour chosen solvent into conical flask and warm.
2. If flammable, warm solvent over water bath.
3. Tip impure sample into second conical flask.
4. Slowly add minimum volume of solvent into impure sample until it dissolves.
5. Allow it to cool and crystals of desired product form in beaker.
6. Filter crystals under reduced pressure to obtain dry crystalline solid.

Question 3

Determination of Melting Point

Answer 3

• Melting range - Difference between temperatures at which a compound begins to melt and finishes melting.
1. Ensure sample is fully dry.
2. Hold one end of glass capillary tube in hot Bunsen flame until fully sealed.
3. Allow tube to cool and fill up to 3mm of crystals into the tube.
• Electric Apparatus.
1. Place tube into sample hole and 0-300°C thermometer into thermometer hole.
2.Using rapid heating setting, allow sample to heat and observe via magnifying window.
3. Record melting point, let apparatus cool and continue heating the sample.
4. As melting point approaches, raise temperature highly whilst observing.
• Oil Bath
1. Set up oil bath, attach capillary tube containing sample to thermometer using rubber band and clamp the thermometer.
2. End of thermometer and and of capillary tube should touch oil.
3. Slowly heat side of oil bath using micro-burner whilst observing solid.
4. Once it starts to melt, remove heat and record °C.
5. Slowly heat oil until solid completely melted.