Combining Half-Equations

Oxidation of alcohols Answers

1. Write an equation for each of the following reactions.

a) Ethanol is warmed with excess sodium dichromate solution in the presence of dilute acid.

2– + – 3+ Reduction: Cr2O7 + 14 H + 6 e → 2 Cr + 7 H2O

+ – Oxidation: CH3CH2OH + H2O → CH3COOH + 4 H + 4 e

2– + 3+ 3 CH3CH2OH + 2 Cr2O7 + 16 H → 3 CH3COOH + 4 Cr + 11 H2O

b) Butan-2-ol is mixed with acidified potassium permanganate solution.

– + 2+ – Reduction: MnO4 + 8 H → Mn + 4 H2O + 5 e

+ – Oxidation: CH3CH2CHOHCH3 → CH3CH2COCH3 + 2 H + 2 e

– + 2+ 5 CH3CH2CHOHCH3 + 2 MnO4 + 6 H → 5 CH3CH2COCH3 + 2 Mn + 8 H2O

c) Methanol is reacted with a limited amount of hydrogen peroxide solution at room temperature.

+ – Reduction: H2O2 + 2 H + 2 e → 2 H2O

+ – Oxidation: CH3OH → CH2O + 2 H + 2 e

CH3OH + H2O2→ CH2O + 2 H2O

d) Pentan-1-ol is heated with acidified potassium permanganate solution.

– + 2+ – Reduction: MnO4 + 8 H → Mn + 4 H2O + 5 e

+ – Oxidation: CH3(CH2)3CH2OH + H2O → CH3(CH2)3COOH + 4 H + 4 e

– + 2+ 5 CH3(CH2)3CH2OH + 4 MnO4 + 12 H → 5 CH3(CH2)3COOH + 4 Mn + 11 H2O

© WestOne Services 2010 SCIENCE1163 1 2. For each of the following situations write an equation for the reaction that would occur and predict observations. If no reaction occurs write ‘no reaction’ and explain your reasoning.

a) Methanol is warmed with excess sodium dichromate solution in the presence of dilute acid.

2– + 3+ Equation Cr2O7 + 3 CH3OH + 8 H → 2 Cr + 3 CH2O + 7 H2O

Observation orange solution becomes green

b) 2,2-dimethylbutan-3-ol is warmed with excess sodium dichromate solution in the presence of dilute sulfuric acid.

2– + 3 CH3C(CH3)2CHOHCH3 + Cr2O7 + 8 H → Equation 3+ 3 CH3C(CH3)2COCH3 + 2 Cr + 7 H2O

Observation orange solution becomes green

c) Methylpropan-2-ol is warmed with excess acidified potassium permanganate solution.

Equation No reaction. Methylpropan-2-ol is a tertiary alcohol.

Observation