2. 7 Alcohols and Carboxylic Acids

Question 1

What is the functional group of alcohols?

Answer 1

-OH

Question 2

What is the general formula for alcohols?

Answer 2

C(n)H(2n+1)OH

Question 3

What are the conditions for the industrial production of ethanol from ethene?

Answer 3

Hydration of ethene:
- Phosphoric acid catalyst (aqueous)
- Temperature of 300oC and high pressure

Question 4

Write the chemical equation for the hydration of ethene

Answer 4

Question 5

How can ethanol be produced from a renewable source?

Answer 5

Ethanol can be produced from the fermentation of sugars. In crops, enzymes break down starch into sugars which can then undergo fermentation to form ethanol.

Question 6

What conditions are required for the fermentation of glucose to form ethanol?

Answer 6

• Carried out with yeast
• 30-40oC temperature
• Anaerobic conditions (no oxygen)

Question 7

What is the chemical equation for the fermentation of glucose to form ethanol?

Answer 7

C(6)H(12)O(6) → 2C(2)H(5)OH + 2CO(2)

Question 8

After fermentation, how can ethanol be separated from the rest of the reaction mixture?

Answer 8

Distillation

Question 9

Why is the production of ethanol fuel from glucose said to be ‘carbon neutral’?

Answer 9

A process is carbon neutral if it contributes no net increase to the amount of carbon dioxide in the atmosphere.
Ethanol fuel, produced from glucose, is carbon neutral because the crops take in carbon dioxide during photosynthesis which balances out the amount of carbon dioxide that is released when the fuel is burned.

Question 10

Why might someone argue that the production of ethanol fuel from glucose is not carbon neutral?

Answer 10

Energy is required to power the machinery to make fertilisers for the crops and to harvest the crops, which releases carbon dioxide. Similarly, more carbon dioxide is released during the transportation of the ethanol.

Question 11

What is formed when alcohols undergo dehydration?

Answer 11

Alkenes

Question 12

How do alcohols undergo dehydration reactions?

Answer 12

Alcohols undergo dehydration reactions to form an alkene and a water molecule.
There are two ways to carry out dehydration:
- Heat with strong acid catalyst.
- Pass alcohol vapour over Al2O3 powder.

Question 13

What is the chemical equation for the dehydration of propan-2-ol to form prop-2-ene?

Answer 13

Question 14

Explain the classification of alcohols

Answer 14

Question 15

How are primary alcohols oxidised to carboxylic acids?

Answer 15

If a primary alcohol is heated under reflux with acidified potassium dichromate(VI), the alcohol will be oxidised form a carboxylic acid.
CH(3)CH(2)OH + 2[O] → CH(3)COOH + H(2)O
The acidified potassium dichromate(VI) will change colour from orange to green.

Question 16

How are secondary alcohols oxidised to ketones?

Answer 16

If a secondary alcohol is heated under reflux with acidified potassium dichromate (VI), the alcohol will be oxidised to form a ketone:
CH(3)CH(OH)CH(3) + [O] → CH(3)COCH(3) + H(2)O
The acidified potassium dichromate(VI) will change colour from orange to green.

Question 17

What qualitative test can be carried out to test for primary and secondary alcohols?

Answer 17

Add acidified potassium dichromate(VI):
The solution will change colour from orange to green if a primary or secondary alcohol is present.

Question 18

What qualitative test can be carried out to test for carboxylic acids?

Answer 18

Add sodium hydrogencarbonate (NaHCO3):
The solution will effervesce and carbon dioxide will be produced if a carboxylic acid is present. The gas released can be tested with limewater to identify it as carbon dioxide.

Question 19

What is produced when carboxylic acids react with bases?

Answer 19

Salt and water

Question 20

What is the chemical equation for the reaction of ethanoic acid with sodium hydroxide?

Answer 20

Question 21

What is produced when carboxylic acids react with carbonates?

Answer 21

Salt, carbon dioxide and water

Question 22

What is the chemical equation for the reaction of methanoic acid with sodium carbonate?

Answer 22

Question 23

What is produced when carboxylic acids react with hydrogencarbonates?

Answer 23

Salt, carbon dioxide and water

Question 24

What is the chemical equation for the reaction of ethanoic acid with sodium hydrogencarbonate?

Answer 24

Question 25

How do alcohols react with carboxylic acids?

Answer 25

Alcohols react with carboxylic acids to form esters. This process is called esterification and requires heating with a sulfuric acid catalyst.

Question 26

What is the chemical equation for the reaction between methanol and ethanoic acid? Give the name of the ester formed

Answer 26

Question 27

Explain how ethanol can be separated from water

Answer 27

Ethanol and water have different boiling points so they can be separated by distillation:
- The mixture is heated until the ethanol evaporates.
- The ethanol vapours enter the condenser where
they condense and run into a beaker.