Chemistry 5070 · O Level · Acid–base titrations

Acid–base titrations — practice question

Solution K is an aqueous sodium hydroxide, $\text{NaOH}$, solution. A student finds the concentration of solution K by titration.
(a)[1]

Explain why a pipette is selected rather than a measuring cylinder for measuring $25.0\,\text{cm}^3$ of solution K.

(b)[1]

Name the vessel used to prepare solution L.

(c)[1]

Identify the liquid used to rinse the pipette.

(d(i))[1]

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

(d(ii))[1]

State the colour change shown by the methyl orange indicator at the end-point.

(e)[4]

Use the diagrams to fill in the table and work out the average volume of $\text{H}_2\text{SO}_4(aq)$ added.

(f)[1]

Calculate the amount of substance of $\text{H}_2\text{SO}_4$ present in the average volume of $0.100\,\text{mol dm}^{-3}$ $\text{H}_2\text{SO}_4(aq)$.

(g)[1]

Use $2\text{NaOH} + \text{H}_2\text{SO}_4 \rightarrow \text{Na}_2\text{SO}_4 + 2\text{H}_2\text{O}$ to find the number of moles of $\text{NaOH}$ in $20.0\,\text{cm}^3$ of solution L.

(h)[1]

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

(i)[1]

Deduce how many moles of $\text{NaOH}$ are in $25.0\,\text{cm}^3$ 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 $\text{H}_2\text{SO}_4(aq)$ becomes smaller, larger, or unchanged when 20 drops of methyl orange are used, and explain your answer.

Worked solution & mark scheme

This 16-mark question has a full step-by-step worked solution and mark scheme. One marking point: A pipette is more accurate ORA

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