IB Chemistry HL 3.1.9 pOH scale Question Bank

Practise IB Chemistry HL 3.1.9 by applying poh scale to exam-style questions.

Exam points

identify the relevant chemical structure, process or evidence
apply the correct chemical model or equation
evaluate the result using chemical reasoning and data

[Maximum number: 2]

Methanoic acid is a monoprotic weak acid.

The concentration of methanoic acid was found by titration with a $0.200 \mathrm{~mol} \mathrm{dm}^{-3}$ standard solution of sodium hydroxide, NaOH(aq), using an indicator to determine the end point.

Calculate the pH of the sodium hydroxide solution.

$[\mathrm{OH^-}]=0.200\ \mathrm{mol\ dm^{-3}}$

Alternative 1:
$\mathrm{pOH}=-\log(0.200)=0.699$ $\mathrm{pH}=14.000-0.699=13.301$

Alternative 2:
$[\mathrm{H^+}]=\frac{1.00\times10^{-14}}{0.200} =5.00\times10^{-14}\ \mathrm{mol\ dm^{-3}}$ $\mathrm{pH}=-\log(5.00\times10^{-14})=13.301$

Award [2] for correct final answer.

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3.1.9 (HL)—pOH scale question 1