Chemistry 5070 · O Level · Acid–base titrations

Acid–base titrations — practice question

Limestone is calcium carbonate that is not pure. A student carries out an experiment to determine the percentage by mass of calcium carbonate in a limestone sample. The limestone is put into a container that has already been weighed, and the container is weighed again. mass of container + limestone = $10.22\text{ g}$ mass of empty container = $5.72\text{ g}$
(a)[1]

Calculate the mass of limestone taken for the experiment.

(b)[1]

Name the vessel that should be used to prepare solution $T$.

(c)[1]

What colour change is seen for the methyl orange at the end-point?

(d)[4]

Use the diagrams to complete the results table and find the mean volume of $0.100\text{ mol dm}^{-3}$ sodium hydroxide.

(e)[1]

Calculate the amount in moles of sodium hydroxide in the average volume of $0.100\text{ mol dm}^{-3}$ sodium hydroxide in (d).

(f)[1]

Using the equation $\text{NaOH} + \text{HCl} \rightarrow \text{NaCl} + \text{H}_2\text{O}$ and your answer to (e), deduce the amount in moles of hydrochloric acid in $25.0\text{ cm}^3$ of $T$.

(g)[1]

Calculate the amount in moles of hydrochloric acid in $250\text{ cm}^3$ of $T$.

(h)[1]

Calculate the amount in moles of hydrochloric acid present in the original $50.0\text{ cm}^3$ of $2.00\text{ mol dm}^{-3}$ hydrochloric acid.

(i)[1]

Using your answers to (h) and (g), calculate the amount in moles of hydrochloric acid that reacted with the calcium carbonate in the sample of limestone.

(j)[1]

Using the equation $\text{CaCO}_3 + 2\text{HCl} \rightarrow \text{CaCl}_2 + \text{CO}_2 + \text{H}_2\text{O}$ and your answer to (i), calculate the amount in moles of calcium carbonate that reacted with the hydrochloric acid.

(k)[1]

Calculate the relative formula mass for calcium carbonate. $[A_r: \text{Ca}, 40; \text{C}, 12; \text{O}, 16]$

(l)[1]

Using your answers to (j) and (k), calculate the mass of calcium carbonate in the sample of limestone.

(m)[1]

Using your answers to (a) and (l), calculate the percentage by mass of calcium carbonate in the sample of limestone.

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