Topic 16: Hydroxy Compounds

Question 1

Definitions I:
(a) Alcohol
(b) Primary alcohol
(c) Dehydration

Answer 1

Definitions I:
(a) Organic compound with a hydroxyl group (-OH) on an alkyl chain.
(b) Alcohol with -OH on carbon bonded to one alkyl group.
(c) Removal of H₂O from an alcohol to form an alkene.

Question 2

Write equations for producing ethanol:
(a) From ethene [1 Mark]
(b) From ethanoic acid [1 Mark]

Answer 2

(a) CH₂=CH₂ + H₂O → CH₃CH₂OH (H₃PO₄, steam) (1 mark)
(b) CH₃COOH + 4[H] → CH₃CH₂OH + H₂O (LiAlH₄) (1 mark)

Question 3

Classify and predict the oxidation products of:
(a) CH₃CH₂OH with K₂Cr₂O₇/H⁺ [1 Mark]
(b) (CH₃)₂CHOH with KMnO₄/H⁺ [1 Mark]

Answer 3

(a) Primary, CH₃CH₂OH → CH₃CHO (distil), then CH₃COOH (reflux) (1 mark)
(b) Secondary, (CH₃)₂CHOH → (CH₃)₂C=O (distil) (1 mark)

Question 4

In a lab, propan-1-ol reacts with HBr(g). Write the equation and conditions. [2 Marks]

Answer 4

CH₃CH₂CH₂OH + HBr → CH₃CH₂CH₂Br + H₂O (1 mark)
Gas, room temp (1 mark)

Question 5

Describe the combustion of ethanol in a car engine and its products. [2 Marks]

Answer 5

CH₃CH₂OH + 3O₂ → 2CO₂ + 3H₂O (complete) (1 mark)
CO if incomplete, exothermic (1 mark)

Question 6

Show the esterification of ethanol with CH₃COOH, including catalyst and product name. [2 Marks]

Answer 6

CH₃CH₂OH + CH₃COOH → CH₃COOCH₂CH₃ + H₂O (H₂SO₄) (1 mark)
Ethyl ethanoate (1 mark)

Question 7

How does CH₃CH₂OH react with Na(s) in a fume hood? Include observations. [3 Marks]

Answer 7

2CH₃CH₂OH + 2Na → 2CH₃CH₂ONa + H₂ (1 mark)
Bubbles of H₂ gas (1 mark)
White solid (sodium ethoxide) forms (1 mark)

Question 8

Why is ethanol more acidic than water, and how does it compare? [2 Marks]

Answer 8

C-O-H bond weaker than H-O-H, more H⁺ release (1 mark)
Still weak acid, less acidic than phenols (1 mark)

Question 9

In a test, CH₃CH(OH)CH₃ with I₂/OH⁻ gives a precipitate. What’s formed, and why? [2 Marks]

Answer 9

CH₃CH(OH)CH₃ + 4I₂ + 6OH⁻ → CHI₃ + CH₃CO₂⁻ + 5I⁻ + 5H₂O (1 mark)
Yellow ppt (CHI₃), CH₃CH(OH)- oxidised (1 mark)

Question 9

Write the dehydration equation for butan-2-ol with Al₂O₃, heat. [2 Marks]

Answer 9

CH₃CH(OH)CH₂CH₃ → CH₃CH=CHCH₃ + H₂O (Al₂O₃, heat) (1 mark)
But-2-ene forms (1 mark)

Question 10

Predict the product when CH₃CH₂CH₂Cl reacts with NaOH(aq), heat, and classify the alcohol. [2 Marks]

Answer 10

CH₃CH₂CH₂Cl + NaOH → CH₃CH₂CH₂OH + NaCl (heat) (1 mark)
Primary alcohol (1 mark)

Question 10

Compare the oxidation of CH₃CH₂OH and (CH₃)₃COH with K₂Cr₂O₇/H⁺, reflux. [3 Marks]

Answer 10

CH₃CH₂OH (primary) → CH₃COOH, orange to green (1 mark)
(CH₃)₃COH (tertiary) no reaction, stays orange (1 mark)
Tertiary lacks H on C-OH for oxidation (1 mark)