DP Chemistry (first assessment 2025)

Question 21M.2.SL.TZ1.b(ii)

Date	May 2021	Marks available	[Maximum mark: 1]	Reference code	21M.2.SL.TZ1.b(ii)
Level	SL	Paper	2	Time zone	TZ1
Command term	Demonstrate	Question number	b(ii)	Adapted from	N/A

b(ii).

[Maximum mark: 1]

21M.2.SL.TZ1.b(ii)

Saturated aqueous hydrogen sulfide has a concentration of 0.10 mol dm⁻³ and a pH of 4.0. Demonstrate whether it is a strong or weak acid.

[1]

Markscheme

weak AND strong acid of this concentration/[H⁺] = 0.1 mol dm⁻³ would have pH = 1
OR
weak AND [H⁺] = 10⁻⁴ < 0.1 «therefore only fraction of acid dissociated» ✔

Syllabus sections

Reactivity 3. What are the mechanisms of chemical change? » Reactivity 3.1—Proton transfer reactions » Reactivity 3.1.4—The pH scale can be used to describe the [H+] of a solution: pH = –log10[H+]; [H+] = 10–pH. Perform calculations involving the logarithmic relationship between pH and [H+].

Reactivity 3. What are the mechanisms of chemical change? » Reactivity 3.1—Proton transfer reactions » Reactivity 3.1.6—Strong and weak acids and bases differ in the extent of ionization. Recognize that acid–base equilibria lie in the direction of the weaker conjugate. and are strong acids, and group 1 hydroxides are strong bases.

Question 21M.2.SL.TZ1.b(ii)

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