Chemistry 5070 · O Level · Acid–base titrations

Acid–base titrations — practice question

A student is working out the percentage by mass composition of a mixture made from two solids, sodium chloride, $\text{NaCl}$, and sodium carbonate, $\text{Na}_2\text{CO}_3$. This mixture is M.
(a)[1]

Calculate the mass of M that was used in the experiment.

(b)[1]

Name the apparatus in which solution Q should be made up to $250\,\text{cm}^3$.

(c)[1]

What is the colour of the solution in the conical flask before hydrochloric acid is added, and what colour is seen at the end-point?

(d)[4]

Use the diagrams to fill in the titration table and work out the average volume of hydrochloric acid needed.

(e)[1]

Calculate the number of moles of hydrochloric acid in the average volume of $0.100\,\text{mol dm}^{-3}$ hydrochloric acid in (d).

(f)[1]

Construct the equation for the reaction of sodium carbonate, $\text{Na}_2\text{CO}_3$, with hydrochloric acid.

(g)[1]

Using the information in (f) together with your answer to (e), determine the number of moles of sodium carbonate in $25.0\,\text{cm}^3$ of Q.

(h)[1]

Calculate the number of moles of sodium carbonate in $250\,\text{cm}^3$ of Q.

(i)[1]

Use your answer to (h) to work out the mass of sodium carbonate, $\text{Na}_2\text{CO}_3$, in the sample of M. [$A_r$: Na, $23$; C, $12$; O, $16$]

(j)[1]

Using your answers to (i) and (a), work out the mass of sodium chloride in the sample of M.

(k)[1]

Calculate the percentage by mass of sodium chloride present in M.

Worked solution & mark scheme

This 14-mark question has a full step-by-step worked solution and mark scheme. One marking point: The mass is 1.82 g.

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