Alcohols, Carboxlyic Acids and esters

Question 1

Preparation of ethanol:

a) Addition reaction of ethane with steam(hydration)

Answer 1

Condition: 300 degrees celcius, phosphoric Acid catalyst, 60atm

Question 2

Preparation of ethanol:

b) Fermentation of glucose

Answer 2

Fermentation is the process in which micro-organisms such as yeast act on carbohydrates like glucose in the absence of oxygen to produce ethanol and carbon dioxide.

Question 3

Precautions for fermentation of glucose:

a) temperature of fermentation set up must be kept at around 37 degrees celcius

Answer 3

What happens when the reaction proceeds beyond the optimal operating temp(37 degrees celcius)?
When the alcohol content exceeds 15%, the years catalysing the reaction will denature, preventing further fermentation.

Question 4

Precautions:

b) Fermentation can only take place in the absence of oxygen, hence the set up must be air tight

Answer 4

1) conical flask is tightly fitted with a rubber bung
2)Delivery tube submerged into limewater prevents air from entering apparatus.
Reason: In the presence of air, bacteria in the air can oxidise ethanol to ethanoic acid

Question 5

Why is fractional distillation required for the fermentation process?

Answer 5

To remove ethanol to lower the alcohol content, in order to allow the process to continue.

Question 6

b) List two advantages of fermentation of glucose over hydration if alkenes.

Answer 6

1) Sugar as a raw material, is a renewable resource whereas alkenes, from cracking of cruise oil is finite
2) Environmentally friendly industry as photosynthesis has to be carried out to obtain sugar

Question 7

What is one limitation of fermentation of glucose to produce alcohol

Answer 7

Only ethanol, and no other alcohol is produced

Question 8

Chemical reaction of alcohols

i) Combustion reactions

Answer 8

Alcohols combust readily to form carbon dioxide and water vapour

Question 9

ii) Oxidation reactions(using oxidising agent)

Answer 9

Alcohols undergo oxidation when heated with an oxidising agent such as acidified potassium mangante(VII) under reflux to form carboxlyic acid and water.
As ethanol is oxidised to ethanoic acid, acidified potassium manganate(VII) changes from purple to colourless.

Question 10

b) Oxidation reactions(using atmospheric oxygen)

Answer 10

Alcohols can also be oxidised using atmospheric oxygen to produce carboxlyic acids, although this is a far slower process

Eg: Ethanol, when exposed to air, oxidises to form ethanoic acid

Question 11

Uses of carboxlyic acids

Answer 11

• Ethanoic acid is used in food as a flavouring and preservative
• Amino acids are used by the body to make proteins

Question 12

General formula and properties of carboxlyic acids going down the homologous series:

Answer 12

General formula:CnH2n+1COOH

• Carboxlyic acid chain gets longer by a -CH2 unit
• Size or molecule increases( Mr increases by 14)
• Boiling points increases( higher than corresponding alcohol)
• Solubility in water decreases.

Melting points of carboxlyic acids do not necessarily increase going down the series.

Question 13

Chemical properties of carboxlyic acids

Answer 13

Carboxlyic acids are weak acids, undergoing only partial dissociation, in water, to produce H+- ions. They undergo the SMEs reactions as other acids
-reaction with reactive metals:
Ethanoic acid + magnesium——— magnesium ethanoate + hydrogen

• Reaction with carbonates:
  Ethanoic acid + sodium carbonate————— sodium ethanoate+ carbon dioxide + water

-Reaction with bases:
Ethanoic acid+ sodium hydroxide —————sodium ethanoate + water

Question 14

Magnesium ribbon is added to separate samples of hydrochloric acid and Ethanoic acid of equal concentrations. How would you expect the speed of the reaction to duffer for the two reactions

Answer 14

The speed of reaction for hydrochloric acid would be faster. Hydrochloric acid is a strong acid that undergoes complete dissociation . The number of H+ ions per unit volume would be higher. Thus, the frequency of effective collisions with Mg would be higher

Question 15

Esterfication

Answer 15

Alcohols also react with carboxlyic acids to produce an ester and water
Ethanoic acid + methanol——— methyl ethanoate + water

Conditions:
Heat under reflux
Concentrated sulfuric acid catalyst

Question 16

Esterfication

Answer 16

Alcohols also react with carboxlyic acids to produce an ester and water
Ethanoic acid + methanol——— methyl ethanoate + water

Conditions:
Heat under reflux
Concentrated sulfuric acid catalyst

Question 17

Apparatus for esterfication:

Answer 17

Condensation to allow mixture to reflux>prevents the escape of unreacted vapours
Water bath> to prevent direct heating, so that the reactants doesn’t not ignite

Question 18

Users of esters

Answer 18

Used to manufacture perfumes

Artificial food flavouring for sweets, drinks and cakes

Question 19

Physical properties of esters

Answer 19

• Esters are fairly soluble in water. However, solubility decreases as Mr increases
• Esters are also soluble in organic solvents and are themselves good organic solvents
• Esters are neutral to litmus tests
• Esters have relatively Low boiling points.

Question 20

Tips when drawing Esters

Answer 20

Always draw carboxlyic chain first then alcohol chain
When it comes to naming Esters, alcohol name comes first
Eg: Ethanoic acid +methanol———- methyl ethanoate + water