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

1. Pour the mixture into a separating funnel and some distilled water
2. Add the stopper and invert the flask to mix the mixture
3. Equalise the pressure by opening the stopper as required
4. Continue shaking until there is no ‘whistle’ sound
5. To collect the water in the lower layer, open the stopper and place a beaker under the spout
6. Use another beaker to collect the desired organic layer
7. 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 the organic product
If the drying agent forms clumps add some 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 hydrocarbon be tested? What are the observations?

Answer 7

Use bromine water
Add few drops of bromine water to the sample and mix well
Positive test - bromine water turns colourless

Question 8

What are the reagents used to test haloalkanes and what are the 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’ reagent

Question 10

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

Answer 10

Ketones - no change
Aldehyde - turns from orange to green colour

Question 11

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

Answer 11

Ketones - no change
Aldehyde - dark red precipitate

Question 12

What are the observations when Tollens’ reagent is reacted with ketones and aldehydes?

Answer 12

Ketones - no silver mirror
Aldehydes - silver mirror

Question 13

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

Answer 13

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