O- Alcohols =)

Question 1

In industry, this fermentation reaction is carried out at 35oC rather than 25oC.
Suggest one advantage and one disadvantage for industry of carrying out the fermentation at this higher temperature. (2)

Answer 1

➕ faster prod. of ethanol
➖↑ energy required in the reaction

Question 2

A student carrued out fermentation of glucose in a beaker, resulting in ethanol being contaminated.
Suggest why. (1)

Answer 2

air gets in –> oxidation occurs

Question 3

Ethanol cab be produced from the hydration of ethene.
Deduce how an overall yield of 95% is achieved in this process without changing the operating conditions. (1)

Answer 3

recirculate unreacted ethene

Question 4

In order to ensure that the oxidation to ethanoic acid is complete, the reaction is carried out under reflux.
Describe what happens when a reaction mixture is refluxed and why it is necessary in this case. (3)

Answer 4

• mixture of liquids is heated to bp for a long time
• vapour formed escapes from liquid mixture –> converted back into liquid + returned to mixture
• any ethanol + ethanal evaporated ✔ oxidised

Question 5

Anti-bumping granules are placed in the flask when refluxing.
Suggest why these granules prevent bumping. (1)

Answer 5

prevent large bubbles

Question 6

State a simple chemical test that distinguishes the propanoic acid from the
propan-1-ol.
Give one observation for the test with each substance. (3)

Answer 6

• add sodium carbonate/ hydrogencarbonate
• acid: effervescence
• alcohol: x visible change

Question 7

What is the problem caused if the direction of water flowing through the condenser is wrong in distillation? (1)

Answer 7

• condenser x cool enough
• product may not condense

Question 8

What is the purpose of a closed system with a thermometer in distillation? (1)

Answer 8

• allow collection of product (propanone) only
• stay in suitable temp range

Question 9

Give a reagent (or combination of reagents) that could be added separately to each compound to distinguish between a ketone and an acid.
State observations. (2)

Answer 9

• sodium carbonate/ hydrogencarbonate
• no visible reaction vs effervescence

Question 10

Cyclohexene is prepared by the dehydration of cyclohexanol using concentrated phosphoric acid as a catalyst.
State how and explain why cyclohexene can be
separated from the reaction mixture. (2)

Answer 10

• separated by (fractional) distillation
• lowest bp

Question 11

There is a very low yield of butan-1-ol from but-1-ene.
Explain why. (2)

Answer 11

• formed via ↓ stable carbocation
• primary x secondary

Question 12

Give 2 ways of maximising the yield of propanal obtained by distillation of the reaction mixture containing propanal and propan-1-ol. (2)
{boiling point of propanal < propan-1-ol}

Answer 12

1. keep temp of mixture < bp of propan-1-ol
2. cool distillate

Question 13

Write a half-equation for the overall oxidation of ethanol into ethanoic acid. (1)

Answer 13

CH3CH2OH + H2O –> CH3COOH + 4H+ + 4e-