DP Chemistry (first assessment 2025)

Question 19M.2.SL.TZ2.a(ii)

Date	May 2019	Marks available	[Maximum mark: 1]	Reference code	19M.2.SL.TZ2.a(ii)
Level	SL	Paper	2	Time zone	TZ2
Command term	State	Question number	a(ii)	Adapted from	N/A

a(ii).

[Maximum mark: 1]

19M.2.SL.TZ2.a(ii)

The hydrogencarbonate ion, produced in Equilibrium (2), can also act as an acid.

State the formula of its conjugate base.

[1]

Markscheme

CO₃^2- [✔]

Examiners report

More than half the candidates were able to deduce that carbonate was the conjugate base but a significant proportion of those that did, wrote the carbonate ion with an incorrect charge.

Syllabus sections

Reactivity 3. What are the mechanisms of chemical change? » Reactivity 3.1—Proton transfer reactions » Reactivity 3.1.2—A pair of species differing by a single proton is called a conjugate acid–base pair. Deduce the formula of the conjugate acid or base of any Br.nsted–Lowry base or acid.

Question 19M.2.SL.TZ2.a(ii)

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