11. Alcohols

Question 1

Advantages of Direct Hydration:

Answer 1

• high purity ethanol made
• continuous production method
• fast (high rate of reaction)

Question 2

Disadvantages of Direct Hydration:

Answer 2

• crude oil = non-renewable
• high pressure + temp = expensive as it needs lots of energy
• high tech equipment needed = expensive

Question 3

Photosynthesis Equation:

Answer 3

6CO2 + 6H2O -> C6H12O6 + 6O2

Question 4

Fermentation Equation:

Answer 4

C6H12O6 -> 2CH3CH2OH + 2CO2

Question 5

Combustion Equation:

Answer 5

2CH3CH2OH + 6O2 -> 4CO2 + 2H2O

Question 6

Why isn’t bio-ethanol considered carbon neutral?

Answer 6

Process involved in the production and distribution of bioethanol require fossil fuels that release CO2 (e.g harvesting, transport, extracting)

Question 7

Advantages of Fermentation:

Answer 7

• uses renewable energy (glucose)
• lower temp = less energy = low cost
• low tech equipment = cheaper

Question 8

Disadvantages of Fermentation:

Answer 8

• land used to grow crops isn’t available for food production
• impure ethanol made needs distilling
• low yield
• slow rate of reaction

Question 9

Features and Purpose of a Condenser:

Answer 9

Features:
- open at both ends
- cold water flows around outside
Purpose:
- cools hot vapour + condenses back into liquid

Question 10

Purpose of Antibumping Granules:

Answer 10

Prevents formation of larger bubbles

Question 11

Reflux Steps:

Answer 11

1. aldehyde vapour rises and enters condenser
2. aldehyde vapour cools and condenses and drops back into reaction mixture

Question 12

Why is reflux used to oxidise a primary alcohol into a carboxylic acid?

Answer 12

Doesn’t allow any remaining reactant vapour to escape

Question 13

Describe what happens when reaction mixture is refluxed and why it’s necessary to complete oxidation for a carboxylic acid

Answer 13

• ethanol + acidified K2Cr2O7 are heated to bpt for prolonged period of time
• ethanal vapour is formed which escapes from liquid reaction mixture and is then condensed back into liquid and returned to reaction mixture

Question 14

Why is distillation used when forming an aldehyde from a primary alcohol?

Answer 14

allows aldehyde vapour to escape reaction mixture and prevents further oxidation

Question 15

Ethanol can be oxidised to ethanal or ethanoic acid. Describe how ethanal can be made in high yield as opposed to ethanoic acid:

Answer 15

• use distillation
• heat to bpt of ethanal
• collect ethanal as its distilled off