DP Chemistry (first assessment 2025)

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Question 21N.2.SL.TZ0.11b

Date	November 2021	Marks available	[Maximum mark: 1]	Reference code	21N.2.SL.TZ0.11b
Level	SL	Paper	2	Time zone	TZ0
Command term	Calculate	Question number	b	Adapted from	N/A

b.

[Maximum mark: 1]

21N.2.SL.TZ0.11b

(b)

The concentration of excess sodium hydroxide was 0.362 mol dm⁻³. Calculate the pH of the solution at the end of the experiment.

[1]

Markscheme

«pOH = –log(0.362) = 0.441»

«pH = 14.000 – 0.441 =» 13.559 ✔

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 3.1.5—The ion product constant of water, Kw, shows an inverse relationship between [H+] and [OH–]. Kw = [H+] [OH–]. Recognize solutions as acidic, neutral and basic from the relative values of [H+] and [OH–].