4.2.3- Organic Synthesis Practical Skills

Question 1

Describe how a Quickfit apparatus is connected

Answer 1

Grease the joints using some petroleum jelly on the inside of the joints before connecting the pieces together

Question 2

In a distillation setup, why is it necessary to have a continuous water flow around the condenser?

Answer 2

So that the water remains cool in order for the mixture to be distilled

Question 3

Describe a method that can be used to separate immiscible liquids

Answer 3

• Pour the mixture into a separating funnel and some distilled water
• Add the stopper and invert the flask to mix the mixture
• Equalise the pressure by opening the stopper as required
• Continue shaking until there is no ‘whistle’ sound
• To collect the water in the lower layer, open the stopper and place a beaker under the spout
• Use another beaker to collect the desired organic layer
• Shake the liquid with some drying agent

Question 4

Name two drying agents

Answer 4

• Magnesium sulphate
• Calcium chloride

Question 5

How to use drying agents

Answer 5

• Add a selected drying agent to organic product
• If the drying agent forms clumps ass dome more until they are moving freely
• Use gravity filtration to collect the dry product
• Filtrate is the product

Question 6

What does re-distillation mean?

Answer 6

When a liquid is purified by using multiple distillations

Question 7

How can unsaturated hydrocarbons be tested? What are observations?

Answer 7

• Use bromine water
• Add a few drops of bromine water to sample and mix well
• Positive result: bromine water turns colourless

Question 8

What are the reagents used to test haloalkanes and what are observations?

Answer 8

Reagents- silver nitrate, ethanol and water
Observations: chloro- white precipitate, bromo- cream precipitate, iodo- yellow precipitate

Question 9

What are the 3 reagents that can be used to test carbonyls?

Answer 9

• Acidified potassium dichromate
• Fehling’s solution
• Tollens’ reagant

Question 10

What are observations when acidified potassium dichromate reacts with ketones and aldehydes?

Answer 10

Ketones- no change
Aldehyde- turns from orange to green

Question 11

What are observations when Fehling’s solutions is reacted with ketones and aldehydes?

Answer 11

Ketones- no change
Aldehyde- dark red precipitate

Question 12

What are observations when Tollens’ reagant reacts with ketones and aldehydes?

Answer 12

Ketones- no silver mirror
Aldehydes- silver mirror

Question 13

What are reagents that can be used to test carboxylic acid? What are observations?

Answer 13

• Universal indicator- pH of weak acid
• Reactive metal- hydrogen effervescence
• Metal carbonate- carbon dioxide effervescence