Chemistry 0620 · IGCSE · Acid–base titrations

Acid–base titrations — practice question

A student prepares crystals of the salt sodium sulfate, $\mathrm{Na_2SO_4}$. The student reacts 0.200 mol/dm$^3$ dilute sulfuric acid, $\mathrm{H_2SO_4(aq)}$, with aqueous sodium hydroxide, $\mathrm{NaOH(aq)}$. The student follows these steps. step 1 The student puts 40.0 cm$^3$ of $\mathrm{NaOH(aq)}$ into a conical flask. This volume contains 0.0100 moles of NaOH. step 2 The student adds a few drops of methyl orange indicator to the $\mathrm{NaOH(aq)}$ in the conical flask. step 3 The student adds 0.200 mol/dm$^3$ $\mathrm{H_2SO_4(aq)}$ to the flask until the end-point is reached. step 4 The student pours the mixture from the conical flask into an evaporating basin and gets dry crystals.
(a)[2]

Complete the symbol equation for the reaction and add state symbols. $\mathrm{H_2SO_4(aq)+2NaOH(aq)\rightarrow Na_2SO_4(\,\,)+\dots(\,\,)}$

(b)[1]

State the type of exothermic reaction taking place.

(c)[1]

Calculate the concentration of $\mathrm{NaOH(aq)}$ used in step 1.

(d)[1]

Name the item of apparatus the student uses to add $\mathrm{H_2SO_4(aq)}$ in step 3.

(e)[2]

Calculate the volume of $\mathrm{H_2SO_4(aq)}$, in cm$^3$, added in step 3.

(f)[2]

State the colour change observed in step 3 from ____ to ____.

(g)[1]

Suggest what the student should do in this additional step to produce white crystals.

(h(i))[2]

Explain the term saturated solution.

(h(ii))[1]

Explain why crystals start to appear as the hot solution cools.

(h(iii))[1]

Suggest the effect, if any, on the mass of crystals collected in step 4 if the solution in the evaporating basin is allowed to dry without gentle heating.

Worked solution & mark scheme

This 14-mark question has a full step-by-step worked solution and mark scheme. One marking point: “M1 correct 2H2O” …

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