9701 · 16.1

Alcohols — practice questions

Practice and worked examples for 9701 Alcohols. Short previews only — attempt the full question in MarkScheme against the official scheme.

Worked example 1

Butan-1-ol is heated under reflux with an excess of acidified potassium dichromate(VI). (i) State the class of butan-1-ol. (ii) Identify the organic product formed. (iii) Write a balanced equation for the reaction. Use [O] to represent the oxidising agent.

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(i) Butan-1-ol is a primary alcohol because the carbon atom attached to the –OH group is bonded to only one other carbon atom.

(ii) Since butan-1-ol is a primary alcohol and it is heated under reflux with excess oxidising agent, it will be fully oxidised to a carboxylic acid. The product is butanoic acid.

(iii) The reaction involves the conversion of the $CH_2OH$ group to a $COOH$ group. This requires two atoms of oxygen from the oxidising agent. $CH_3CH_2CH_2CH_2OH + 2[O] \rightarrow CH_3CH_2CH_2COOH + H_2O$

Worked example 2

Ethanol is warmed with propanoic acid in the presence of a few drops of concentrated sulfuric acid. (i) Name the ester formed. (ii) Draw the displayed formula of the ester.

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(i) The name of the ester comes from the alcohol first, then the carboxylic acid. The alcohol 'ethanol' becomes 'ethyl'. The carboxylic acid 'propanoic acid' becomes 'propanoate'. So the ester is ethyl propanoate.

(ii) The structure is formed by removing a water molecule between the –OH of the propanoic acid and the H of the ethanol's –OH group. Propanoic acid: $CH_3CH_2COOH$ Ethanol: $CH_3CH_2OH$ The ester link is -COO-. The part from the acid is $CH_3CH_2CO-$ , and the part from the alcohol is $-OCH_2CH_3$ . Displayed formula:

    H   H     O    H   H
    |   |    //    |   |
H - C - C - C  - O - C - C - H
    |   |            |   |
    H   H            H   H

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