DP Chemistry (first assessment 2025)

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Question 22M.1A.HL.TZ2.27

Date	May 2022	Marks available	[Maximum mark: 1]	Reference code	22M.1A.HL.TZ2.27
Level	HL	Paper	1A	Time zone	TZ2
Command term	Apply	Question number	27	Adapted from	N/A

27.

[Maximum mark: 1]

22M.1A.HL.TZ2.27

Which species are both Lewis and Brønsted–Lowry bases?

I. CN⁻
II. OH⁻
III. NH₃

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

[1]

Markscheme

D

Examiners report

45% of candidates chose all three species as Lewis and Brønsted-Lowry bases. The most commonly chosen distractor excluded CN^-.

Syllabus sections

Reactivity 3. What are the mechanisms of chemical change? » Reactivity 3.4—Electron-pair sharing reactions » Reactivity 3.4.6—A Lewis acid is an electron-pair acceptor and a Lewis base is an electron-pair donor. Apply Lewis acid–base theory to inorganic and organic chemistry to identify the role of the reacting species.

Reactivity 3. What are the mechanisms of chemical change? » Reactivity 3.1—Proton transfer reactions » Reactivity 3.1.1—Brønsted–Lowry acid is a proton donor and a Brønsted–Lowry base is a proton acceptor. Deduce the Br.nsted–Lowry acid and base in a reaction.