Alcohols

Question 1

What happens to the solubility of alcohols as their carbon chain increases and why?

Answer 1

The solubility in water decreases as it requires more energy to overcome the hydrogen bonds between the alcohol molecules as the molecules are more tightly packed.

Question 2

What is a safe way of disposing of sodium metal?

Answer 2

React it with ethanol

Question 3

What is the first product in the oxidation of a primary alcohol?

Answer 3

An aldehyde and water

Question 4

What product do you get from the oxidation of a primary alcohol under reflux?

Answer 4

A carboxylic acid and water

Question 5

What is the preferred oxidising agent in the oxidation of alcohols?

Answer 5

Potassium Dichromate (Acidified) or Potassium Manganate (Acidified)

Question 6

What are the products you can obtain from the oxidation of a secondary alcohol?

Answer 6

A ketone and water

Question 7

What is the product from the oxidation of a tertiary alcohol?

Answer 7

No Reaction

Question 8

What is the reagent and the colour change when testing for a primary or secondary alcohol?

Answer 8

Potassium dichromate (acidified) turns from orange to green.

Question 9

What are the two tests for aldehydes and what are their colour changes?

Answer 9

Tollen’s reagent forms a silver mirror when aldehydes are present.

Fehling’s solution forms a red precipitate if aldehydes are present.

With ketones there is no reaction here.

Question 10

What are the two ways to make ethanol?

Answer 10

Fermentation of carbohydrates

Hydration of ethene

Question 11

What are the conditions needed for the fermentation of carbohydrates to form ethanol?

Answer 11

Temperature: 25-30 degrees
Catalyst: An enzyme in the yeast
Pressure: 1 atm
No oxygen

Question 12

What are the conditions needed for the hydration of ethene to make ethanol?

Answer 12

Temperature: 300 degrees
Catalyst: concentrated H₃PO₄ or H₂SO₄
Pressure: 60 atm

Question 13

What is the mechanism for the hydration of ethene?

Answer 13

Electrophilic addition at 300 degrees and 60 atm with an H₃PO₄ catalyst

Question 14

What is the test for a carboxylic acid?

Answer 14

If you add sodium carbonate it will fizz and produce carbon dioxide.

Question 15

Pros and cons of fermentation to make ethanol?

Answer 15

Pros: Uses renewable materials and takes place at lower temperatures.

Cons: slower than hydration gives less pure ethanol and is batch production.

Question 16

Pros and cons of hydration of ethene?

Answer 16

Pros: Is fast, is continuous, pure and has low labour costs.

Cons: Uses crude oil and requires lots of energy

Question 17

What is the functional group isomer of a secondary alcohol?

Answer 17

ether

Question 18

What is reflux?

Answer 18

When a mixture of liquids is heated to boiling point for a prolonged time under pressure and the liquid which vaporises is changed back into liquid.

Condenser is vertical

Question 19

What do you need to use to reduce a ketone back to a secondary alcohol?

Answer 19

Aqueous NaBH₄

or

NaBH₄ and then HCL