Organic Synthesis Practical Skills

Question 1

Describe how a Quickfit apparatus is connected.

Answer 1

Grease 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 important 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 mixture into a separating funnel and some distilled water
• add 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 water in lower layer, open stopper
• use another beaker to collect the desired organic layer
• shake liquid with some drying agent

Question 4

Name to drying agents

Answer 4

Magnesium sulphate
Calcium chloride

Question 5

How to use drying agents

Answer 5

• add a selected drying agent to the 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 hydrocarbons 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
- iodo — yellow

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 Tollens’ reagent is reacted with ketones and aldehydes?

Answer 11

Ketones — no silver mirror
Aldehydes — silver mirror

Question 12

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

Answer 12

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