4.2.3: Organic synthesis

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 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 is 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
effervescence