Organic 1 Section 3 - Unit 15: Alcohols

Question 1

Explain what is meant by the term dehydration (1 mark)

Answer 1

• Removal of water

Question 2

State the type of compound formed by dehydration of alcohols (1 mark)

Answer 2

• Alkenes

Question 3

Suggest suitable reagent(s) and condition(s) for the dehydration of alcohols (2 marks)

Answer 3

• Concentrated sulphuric acid/concentrated phosphoric acid
• High temperatures/150 – 200°C
• Catalyst - aluminium oxide

Question 4

State what must be added to an aqueous solution of glucose so that ethanol is formed (1 mark)

Answer 4

• Yeast

Question 5

Outline the essential conditions for hydration and fermentation. State the equation for the fermentation reaction. Compare the relative rates and the purity of the product obtained in each case by these two manufacturing processes. (5 marks)

Answer 5

Hydration reaction:
- Water
Fermentation reaction: 
- Yeast
- C6H12O6 → 2C2H5OH + 2CO2
Comparison of reactions:
- The rate of fermentation is slower than hydration
- The product of fermentation is less pure than the product of hydration

Question 6

Ethanoic acid can be formed from bromoethane in two steps. Give reagents and conditions for
each step. Include in your answer the name of the mechanism for the first step and an equation for
the second step (9 marks)

Answer 6

General Equation:
- CH3CH2OH + 2[O] → CH3COOH + H2O (1)

CH3CH2Br (1) to CH3CH2OH (1):

• NaOH (1)
• Aqueous or warm (1)
• Nucleophilic substitution (1)

CH3CH2OH to CH3COOH (1):

• K2Cr2O7 or H2SO4 (1)
• Reflux (1)

Question 7

State the equation and two necessary conditions for a fermentation reaction (3 marks)

Answer 7

• C6H12O6 → 2C2h5OH + 2CO2
• Yeast
• 30°C

Question 8

State the reagent that you would use in the laboratory to oxidise ethanol to ethanoic acid (2 marks)

Answer 8

• Acidified potassium or sodium dichromate

- Orange to green

Question 9

State the meaning of the term carbon-neutral (1 mark)

Answer 9

An activity which has no overall carbon emissions to the atmosphere

Question 10

State and explain the type of bond between H-C-H bond, its shape (3)

Answer 10

• 109.5°
• Tetrahedral
• 4 bonding pairs of electrons are repelling

Question 11

State and explain the type of bond between C-O-H bond, its shape (3)

Answer 11

• 104.5°
• Bent Line
• 2 bonding pairs and 2 lone pairs of electrons

Question 12

Explain why alcohols have high boiling points (3)

Answer 12

• They form hydrogen bonds between other alcohol molecules
• And this bond is strong
• So high amount of energy is needed to overcome it

Question 13

Partial oxidation of Primary Alcohols (5)

• Conditions
• Reagents
• Colour Change

Answer 13

• Aldehyde produced
• K2Cr2O7
• Dilute H2SO4
• Distillation
• Orange to green

Question 14

Full oxidation of Primary Alcohols (5)

• Conditions
• Reagents
• Colour Change

Answer 14

• Carboxylic Acid produced
• K2Cr2O7
• Dilute H2SO4
• Heat under reflux
• Orange to green

Question 15

Oxidation of Secondary Alcohols (4)

• Conditions
• Reagents

Answer 15

• Ketone produced
• K2Cr2O7
• Dilute H2SO4
• Heat under reflux

Question 16

Tollens Reagent (5)

• How it works (3)
• Colour changes (2)

Answer 16

• Contains silver nitrate in NH3
• So oxidises aldehydes
• Not ketones
• So in aldehydes a silver mirror forms
• No change in ketones
• [Ag(NH3)2]+ + e– → Ag + 2NH3

Question 17

Fehling’s Solution (4)

Answer 17

- Contains blue copper (II) ions (gentle oxidising 
agent)
- Reduced to Cu+ ions (brick red)
- Aldehydes - colour change to brick red
- Ketones - no visible change

Question 18

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

Answer 18

CH₃CH₂OH + H₂O –> CH₃COOH + 4H+ + 4e-