organic synthesis and practical skills

Question 1

Describe how a quick-fit apparatus is connected

Answer 1

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

Question 2

In a distillation set up, 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 water to be distilled

Question 3

Name 2 drying agents

Answer 3

1. Magnesium sulphate

2. Calcium chloride

Question 4

How to use drying agents

Answer 4

1. Add a selected drying agent to the organic product
2. If the drying agent forms clumps add some more until they are moving freely
3. Use gravity filtration to collect the dry product
4. Filtrate the product

Question 5

What does re-distillation mean?

Answer 5

When a liquid is purified using multiple distillation s

Question 6

How can unsaturated hydrocarbons be tested? What are the observations?

Answer 6

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

Question 7

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

Answer 7

Reagents: silver nitrate, ethanol and water

Observations:

1. Chlorine - white precipitate
2. Bromine - cream precipitate
3. Iodine - yellow precipitate

Question 8

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

Answer 8

1. Acidified potassium dichromate
2. Fehlings solution
3. Tollens reagent

Question 9

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

Answer 9

Ketones - no change

Aldehyde - turns orange to green colour

Question 10

What are the observations when Fehlings solution reacts with ketones and aldehydes?

Answer 10

Ketones - no change

Aldehyde - dark red precipitate

Question 11

What are the observations when Tollen’s reagent reacts 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

Question 13

How do you test for alcohols

Answer 13

Warm with equal volume of carboxylic acid and a few drops of H2SO4, the sweet smell of an ester after a short time means its present