Drawing and naming the carboxylic acids
5 marks · HardVinegar is commonly used in food and cleaning products.
Name the main carboxylic acid found in vinegar.
State its molecular formula.
Draw the displayed formula for this acid.
Suggest one property of this carboxylic acid that makes it useful in cleaning products.
Explain why this acid is classified as a carboxylic acid, referring to its structure.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) ethanoic acid or acetic acid
(b) C2H4O2
(c) — · must show displayed formula with all bonds, COOH group drawn out
(d) it is a weak acid / reacts with limescale / can neutralise bases
(e) contains the carboxyl functional group (–COOH) attached to a carbon chain; this group has a C=O and an –OH on the same carbon
Must show: all C, H, and O atoms with bonds in displayed formula, COOH group shown correctly in drawing
Common mistakes: Giving 'acetic acid' instead of 'ethanoic acid' (accept as alternative name); Missing the carbon in COOH when naming or drawing formula
Show mark scheme and worked solution
Marking points
A1 (a) · 1 mark · Correct name: ethanoic acid (accept acetic acid).
A2 (b) · 1 mark · Correct molecular formula: C2H4O2
D1 (c) · 1 mark · Fully correct displayed formula: all bonds shown, correct COOH group.
I1 (d) · 1 mark · Property related to acids (e.g., reacts with limescale, neutralises bases, turns blue litmus red).
E1 (e) · 1 mark · Explanation refers to carboxyl group (–COOH) in structure.
Worked solution
a The main carboxylic acid in vinegar is ethanoic acid (accept acetic acid as correct alternative).
b Its molecular formula is C2H4O2.
c Displayed formula:
where all bonds are shown: H O | || H–C–C–O–H | | H H (Structure should clearly show the –COOH group and all bonds).
d One cleaning property is that ethanoic acid is a weak acid and can dissolve limescale (calcium carbonate) or neutralise alkaline substances.
e Ethanoic acid is classified as a carboxylic acid because it contains the carboxyl functional group (–COOH), which consists of a carbon atom double-bonded to an oxygen atom and bonded to an –OH group.