Chemistry 5070 · O Level · Acid–base titrations

Acid–base titrations — practice question

Sample A is an impure form of calcium carbonate. A student works out the amount in moles of calcium carbonate present in a sample of A.
(a)[1]

Calculate the number of moles of HCl added to the beaker when 100 cm^3 of 0.250 mol dm^-3 hydrochloric acid is used.

(b(i))[3]

Complete Table 2.1 by entering the initial and final readings for titration 1, working out the volume of NaOH used in each titration, and placing a tick (✓) next to the best titration results.

(b(ii))[1]

Use the titration results with ✓ to find the mean volume of NaOH used.

(c)[1]

Use your result from (b)(ii) to calculate the number of moles of 0.100\text{ mol dm}^{-3} NaOH that react with 25.0\text{ cm}^3 of B.

(d)[1]

Calculate the amount in moles of NaOH that react with 100\text{ cm}^3 of B.

(e)[1]

Use your answers to (a) and (d) to calculate the number of moles of HCl that react with the calcium carbonate in the sample of A.

(f)[1]

The reaction equation is $\text{2HCl} + \text{CaCO}_3 \rightarrow \text{CaCl}_2 + \text{H}_2\text{O} + \text{CO}_2$. Calculate the number of moles of calcium carbonate in the sample of A.

(g(i))[1]

Give a reason for stirring the reactants together.

(g(ii))[1]

Give a reason for waiting until the effervescence stops.

(h)[2]

Explain why a measuring cylinder gives an inaccurate volume of HCl used. Suggest an improvement.

(i)[1]

Explain why the burette is rinsed with sodium hydroxide after being rinsed with water.

Worked solution & mark scheme

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