Oxidation of Alcohols

Alcohols Worksheet

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1. Naming & Classification

State the name of the following compounds, and state whether they are primary alcohols, secondary alcohols, or tertiary alcohols.

a) CH₃CHOHCH₂CH₃

Butan-2-ol

This is a Secondary alcohol (the carbon attached to the OH group is attached to two other carbons).

b) CH₃COH(CH₃)CH₃

2-methylpropan-2-ol

This is a Tertiary alcohol (the carbon attached to the OH group is attached to three other carbons).

c) CH₂OHC(CH₃)₂CH₃

2,2-dimethylpropan-1-ol

This is a Primary alcohol (the carbon attached to the OH group is attached to only one other carbon).

d) (CH₃)₂CHCH₂OH

2-methylpropan-1-ol

This is a Primary alcohol.

2. Oxidation of Secondary Alcohols

CH₃CHOHCH₂CH₃ is reacted with potassium dichromate with dilute sulfuric acid.

a) State the name of the organic product formed in the reaction.

Butanone

(Note: Secondary alcohols are oxidised to ketones. The name “butan-2-al” does not exist).

b) State what you would observe during the reaction.

Colour change from Orange (Cr₂O₇^2-) to Green (Cr³⁺).

c) Write a symbol equation for the reaction. You may use [O] to represent the oxidising agent.

CH₃CH(OH)CH₂CH₃ + [O] → CH₃COCH₂CH₃ + H₂O

d) Explain why the product can be separated using distillation.

Butan-2-ol (the alcohol) and Butanone (the ketone) have different boiling points due to their intermolecular forces.

Butan-2-ol has hydrogen bonds between molecules due to the O-H group, which are strong. Butanone cannot form hydrogen bonds with itself (it only has permanent dipole-dipole forces), meaning less energy is required to overcome the forces between molecules. Therefore, the ketone has a lower boiling point and can be distilled off.

3. Oxidation of Primary Alcohols

(CH₃)₂CHCH₂OH is reacted with potassium dichromate with dilute sulfuric acid.

a) State the reactants and conditions required to form (CH₃)₂CHCHO.

Acidified sodium/potassium dichromate.

Condition: Warm and Distil immediately (to prevent further oxidation to the carboxylic acid).

b) State the reactants and conditions required to form (CH₃)₂CHCOOH.

Acidified sodium/potassium dichromate (Excess oxidising agent).

Condition: Heat under reflux.

c) Write a symbol equation for the following reactions:

i. Alcohol to Aldehyde:
(CH₃)₂CHCH₂OH + [O] → (CH₃)₂CHCHO + H₂O

ii. Aldehyde to Carboxylic Acid:
(CH₃)₂CHCHO + [O] → (CH₃)₂CHCOOH

iii. Alcohol to Carboxylic Acid (Full Oxidation):
(CH₃)₂CHCH₂OH + 2[O] → (CH₃)₂CHCOOH + H₂O

4. Oxidation of Tertiary Alcohols

CH₃COH(CH₃)CH₃ is reacted with potassium dichromate with dilute sulfuric acid. State the name of the product of this reaction, and draw the skeletal formula.

There is no product.

The reactant is a tertiary alcohol. Tertiary alcohols cannot be oxidised using potassium dichromate because there is no hydrogen atom on the carbon attached to the OH group to remove.

5. Half Equations & Redox

The inorganic reactant for the reactions above is K₂Cr₂O₇.

a) State the role of the K₂Cr₂O₇.

Oxidising Agent

b) State the oxidation state of Chromium in K₂Cr₂O₇ and the oxidation state for the Cr³⁺.

In K₂Cr₂O₇: +6

In Cr³⁺: +3

c) Write a half equation for the reduction of the dichromate ions.

Cr₂O₇^2- + 14H⁺ + 6e^– → 2Cr³⁺ + 7H₂O

d) Write a half equation for the oxidation of ethanol to ethanal.

C₂H₅OH → CH₃CHO + 2H⁺ + 2e^–

e) Write a half equation for the oxidation of ethanol to ethanoic acid.

C₂H₅OH + H₂O → CH₃COOH + 4H⁺ + 4e^–

Mr Cole Chemistry