AQA A-Level Chemistry Paper 3, 2023: Question 16

1 mark · Medium difficulty · Multiple Choice

Brønsted–Lowry Acid Behaviour This question tests the ability to identify which species can donate a proton (H⁺) in an aqueous solution, thereby acting as a Brønsted–Lowry acid.

Practise this question

Question

AQA A-Level Chemistry Paper 3, 2023: Question 16
Question text

16 Which species can behave as a Brønsted–Lowry acid in aqueous solution?

[1 mark]

A SO 2−

B HCO −

C BF3

D NH3

Mark scheme

Show the mark scheme Mark scheme for AQA A-Level Chemistry Paper 3, 2023: Question 16

16 B 1 (AO1) HCO −

How to answer it

Brønsted–Lowry Acids

Question

Which species can behave as a Brønsted–Lowry acid in aqueous solution?

  • A: SO42−
  • B: HCO3−
  • C: BF3
  • D: NH3

Correct Answer: B

The correct answer is HCO3−, as it can donate a proton (H+) in solution, acting as a Brønsted–Lowry acid.

Teacher Tip: Remember that a Brønsted–Lowry acid is defined as a species capable of donating a proton (H+). Always check if the species contains a hydrogen atom that can be released.

Explanation of Other Options

  • A: SO42− cannot donate a proton as it is already a fully deprotonated form of sulfuric acid.
  • C: BF3 is a Lewis acid, not a Brønsted–Lowry acid. It accepts electron pairs rather than donating protons.
  • D: NH3 is a Brønsted–Lowry base as it accepts a proton, forming NH4+.

Key Concept

A Brønsted–Lowry acid must contain a hydrogen atom that can be donated as H+ in solution. For example, HCO3− can act as an acid by donating a proton and forming CO32−.

Final Answer

The correct answer is:

B: HCO3−

Topics

Physical Chemistry · 3.1.12 Acids and Bases

Question and mark scheme from the AQA A-Level Chemistry examination, Paper 3, 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.