Required Practical 4 - Distillation

Question 1

Distillation

Answer 1

• Set up apparatus with a round bottom flask and a horizontal condenser coming off a side arm (thermometer in top)
• Gently heat mixture to a boil
• Volatile components evaporate and condense in cool condenser
• Liquid is collected

Question 2

Reflux

Answer 2

• Set up apparatus with a round bottom flask and a vertical condenser with an open top and anti bumping granules for smoother boiling
• Heat mixture to a boil
• Volatile components evaporate and condense in cool condenser and are returned to flask

Question 3

Suggest purpose of thermometer in distillation

Answer 3

• ensure temperature of vapours remains at or below boiling point of distillate
• only distillate vapours pass through condenser

Question 4

Suggest purpose of fractionating column in distillation

Answer 4

• only distillate vapours pass through

- separated from impurities which condense and return to flask

Question 5

Suggest purpose of condenser in distillation

Answer 5

Cool vapours and condense into liquid

Question 6

Suggest why a fractionating column must be vertical

Answer 6

• condensed liquid returns to flask by gravity

- vapours rise properly

Question 7

Explain when fractional distillation should be used over simple distillation

Answer 7

• boiling points between two liquids is small
• vapours travel a greater distance to condenser
• more surface area for heat exchange between vapours

Question 8

Suggest why the thermometer is placed above rather than inside the boiling flask

Answer 8

To ensure temperature of vapours is measured and not liquid being distilled

Question 9

Suggest why you should never stopper a reflux condenser

Answer 9

Pressure could build up and cause an explosion

Question 10

Suggest precautions taken during distillation

Answer 10

• never distil in an air tight system
• never distil to dryness
• do not fill flask more than two thirds

Question 11

Suggest purpose of anti-bumping granules

Answer 11

• smooth boiling

- provides a surface for bubbles to form (avoids sudden production is large bubbles = bumping)

Question 12

Suggest why it is important to reduce bumping

Answer 12

Severe bumping can lead to loss of product through vents or blow distillation apparatus apart

Question 13

Suggest why organic liquids are not boiled in an open beaker

Answer 13

• highly flammable
• toxic
• loss of organic liquid

Question 14

Suggest sources of error in a distillation

Answer 14

• loss of liquid if vapours escape through loose connectors
• improper thermometer positioning so not calibrated
• temperature variations

Question 15

Suggest why it is important never to distil to dryness

Answer 15

A dry flask will result in a rapid increase in temperature which could cause an explosion