Chemistry 5070 · O Level · Acid–base titrations

Acid–base titrations — practice question

A student carries out an experiment to study the reaction of dilute sulfuric acid with aqueous sodium hydroxide.
(a)[1]

Why was the aqueous sodium hydroxide left for a few minutes before the first portion of sulfuric acid was added?

(b)[1]

What kind of reaction is indicated by the temperature rise?

(c)[1]

Why does the temperature start to fall after $25.0\,\text{cm}^3$ of sulfuric acid has been added?

(d)[3]

Plot temperature against the volume of sulfuric acid added, then find the intersection point.

(e(i))[1]

From your graph, what volume of sulfuric acid is needed to react with all the aqueous sodium hydroxide?

(e(ii))[1]

What temperature does the mixture reach when this volume of sulfuric acid has been added?

(f(i))[1]

Write the equation for the reaction of sulfuric acid with aqueous sodium hydroxide.

(f(ii))[2]

From your equation in (f)(i) and your answer to (e)(i), calculate the concentration of the sulfuric acid used.

(g(i))[1]

Calculate the largest temperature change.

(g(ii))[1]

Calculate the total volume of liquid in the beaker when the temperature reaches its maximum.

(g(iii))[2]

Use the formula $\Delta H = \dfrac{\text{volume in (g)(ii)} \times 4.2 \times \text{temperature change in (g)(i)}}{1000 \times \text{moles of aqueous sodium hydroxide used}}$ to work out the enthalpy change, $\Delta H$, for the reaction.

(h)[3]

Describe how the student can prepare pure dry crystals of sodium sulfate from the solution.

Worked solution & mark scheme

This 18-mark question has a full step-by-step worked solution and mark scheme. One marking point: so that room temperature / a steady temperature could be reached

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