Chapter 16 - Practical techniques

Question 1

What equipment is necessary to heat under reflux ?

Answer 1

• Pear shaped flask
• Condenser
• Rubber tubing
• Stand and clamp
• Heat source (bunsen burner, tripod and gauze OR heating mantle)

Question 2

Which method of heating is used when heating flammable liquids?

Answer 2

Heating mantle so there is no naked flame

Question 3

What is the purpose of heating under reflux ?

Answer 3

• Enables a liquid to be continually boiled whilst the reaction takes place
• Prevents volatile components from escaping and the flask from boiling dry

Question 4

What is the equipment necessary for distillation?

Answer 4

• Pear shaped flask
• Condenser
• Rubber tubing
• Heat source
• Stand and clamp
• Screw cap adaptor
• Receiver adaptor
• Still head
• Thermometer

Question 5

What is the purpose of distillation ?

Answer 5

To separate a pure liquid from its impurities

Question 6

How is an organic product purified?

Answer 6

• Ensure the tap of the separating funnel is closed,Pour the mixture of liquids, place a stopper in the top and invert to mix
• Allow the layers to settle.Add some water to see which layer will increase in volume (aqueous layer)Place a conical flask undeneath, remove the stopper and open the tap until the lower layer has left.Place a second flask underneath to collect the organic layer

Question 7

How can acid impurities be removed?

Answer 7

• Adding aqueous sodium carbonate and shaking the mixture in the separating funnel.
• Carbon dioxide gas is made and must be released via the tap (funnel upside down).
• Aqueous sodium carbonate layer is then removed and organic layer washed with water.

Question 8

How can water be removed from organic products?

Answer 8

• A drying agent is added (typically an anhydrous inorganic salt) and then mixed
• Place a stopper on the flask
• Leave for ten minutes
• Add more until some solid is dispersed as a fine powder
• Decant liquid into another flask.

Question 9

What is a target molecule?

Answer 9

The compound that is being prepared by organic synthesis.

Question 10

How would an aldehyde be formed from a halogenoalkane?

Answer 10

• Stage 1: Add NaOH under reflux to form an alcohol

- Stage 2: Oxidise with acidified potassium dichromate under gentle heat and distill off

Question 11

How would a ketone be formed from an alkene?

Answer 11

• Stage 1: Add steam with acid catalyst to form an alcohol

- Stage 2: Oxidise with acidified potassium dichromate under reflux

Question 12

What is ozonolysis?

Answer 12

A technique used to break open a C=C double bond. Useful for the preparation of aldehydes and ketones.