Chemistry 5070 · O Level · Acid–base titrations

Acid–base titrations — practice question

Solution K is dilute sulfuric acid, $\text{H}_2\text{SO}_4$. A student uses titration to find the concentration of solution K.
(a)[1]

Name a different item of apparatus that could replace a pipette and still measure $20.0\,\text{cm}^3$ of solution K accurately.

(b)[1]

Name the vessel used to prepare solution L.

(c)[1]

A pipette is used to transfer $25.0\,\text{cm}^3$ of solution L into a conical flask. Name the other piece of apparatus used together with the pipette.

(d(i))[1]

State which liquid should be used to rinse the burette out before it is filled with $\text{KOH}(aq)$.

(d(ii))[1]

Explain why the conical flask is put on a white tile.

(d(iii))[1]

State the colour change of the methyl orange indicator at the end-point. The colour changes from [BLANK] to [BLANK].

(e)[4]

Use the burette diagrams to fill in the table, tick the best titration results, and calculate the average volume of $\text{KOH}(aq)$ used.

(f)[1]

Calculate the number of moles of $\text{KOH}$ present in the average volume of $0.100\,\text{mol dm}^{-3}\,\text{KOH}(aq)$ used in (e).

(g)[1]

The reaction equation is $2\text{KOH} + \text{H}_2\text{SO}_4 \rightarrow \text{K}_2\text{SO}_4 + 2\text{H}_2\text{O}$. Use it to work out the number of moles of $\text{H}_2\text{SO}_4$ in $25.0\,\text{cm}^3$ of solution L.

(h)[1]

Calculate the number of moles of $\text{H}_2\text{SO}_4$ present in $250\,\text{cm}^3$ of solution L.

(i)[1]

Deduce the number of moles of $\text{H}_2\text{SO}_4$ in $20.0\,\text{cm}^3$ of solution K.

(j)[1]

Calculate the concentration of solution K in $\text{mol dm}^{-3}$.

(k)[2]

State whether the average titration volume of $\text{KOH}(aq)$ becomes smaller, larger or stays the same when 30 drops of methyl orange are used instead of 3 drops, and explain your answer.

Worked solution & mark scheme

This 17-mark question has a full step-by-step worked solution and mark scheme. One marking point: burette

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