AQA A-Level Chemistry Paper 3, 2021: Question 17
1 mark · Easy difficulty · Multiple Choice
This question focuses on the properties of carboxylic acids and asks you to evaluate several statements about the compound (CH₃)₂CHCH₂COOH. You're expected to use your knowledge of functional groups and molecular interactions to determine which behaviour or property is accurate — such as hydrogen bonding, reactivity, optical activity, or naming conventions.
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Question text
17 Which statement about (CH3)2CHCH2COOH is correct?
[1 mark]
In aqueous solution it reacts with magnesium to form carbon
A
dioxide.
B It can form hydrogen bonds.
C It has optical isomers.
D It has the IUPAC name 2-methylbutanoic acid.
Mark scheme
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17 B 1 It can form hydrogen bonds.
How to answer it
✔ B) It can form hydrogen bonds.
This is correct. The compound contains a -COOH group which has both a hydrogen bonded to oxygen (donor) and a lone pair on oxygen (acceptor), meaning it can form hydrogen bonds with itself or with other molecules.
✘ A) In aqueous solution it reacts with magnesium to form carbon dioxide.
Incorrect. It reacts with magnesium to form a salt and hydrogen gas, not carbon dioxide. Carbon dioxide would be released if it reacted with a carbonate, not a metal.
✘ C) It has optical isomers.
Incorrect. The compound does not have a chiral carbon (a carbon atom bonded to four different groups), so it cannot show optical isomerism.
✘ D) It has the IUPAC name 2-methylbutanoic acid.
Incorrect. The correct name is 3-methylbutanoic acid. The longest chain includes four carbon atoms with the methyl group on the third carbon relative to the carboxylic acid group.
Topics
Organic Chemistry · Physical Chemistry · 3.3.9 Carboxylic Acids and Derivatives · 3.1.3 Bonding
Question and mark scheme from the AQA A-Level Chemistry examination, Paper 3, 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.