Chemistry 5070/31 — October/November 2015

Cambridge O-Level · Practical Test · worked solutions for every part, with the mark scheme

questions

marks

minutes

Topics Experimental Contexts · Observations and Measurements · Analysis, Conclusions and Evaluation · Use of Techniques, Apparatus and Materials · Qualitative Analysis

Q119MExperimental ContextsObservations and MeasurementsAnalysis, Conclusions and EvaluationUse of Techniques, Apparatus and MaterialsFree sample

Calcium carbonate tablets are often taken by people who have stomach pain caused by indigestion. They work by neutralising acid in the stomach and are called antacid tablets.

P is an aqueous solution prepared by reacting two of the antacid tablets with an excess of hydrochloric acid, $\text{HCl}$ . In preparing P, all the calcium carbonate in the two tablets reacted when they were added to $250\text{ cm}^3$ of $0.500\text{ mol / dm}^3$ hydrochloric acid, an excess.

\text{CaCO}_3 + 2\text{HCl} \rightarrow \text{CaCl}_2 + \text{H}_2\text{O} + \text{CO}_2

You are to determine by titration the amount of acid remaining in P.

Q is $0.336\text{ mol / dm}^3$ sodium hydroxide, $\text{NaOH}$ .

(a)

Put P into the burette.

Pipette a $25.0\text{ cm}^3$ (or $20.0\text{ cm}^3$ ) portion of Q into a flask and titrate with P, using the indicator provided.

Record your results in the table, repeating the titration as many times as you consider necessary to achieve consistent results.

Results

Burette readings

titration number	1	2
final reading / $\text{cm}^3$
initial reading / $\text{cm}^3$
volume of P used / $\text{cm}^3$
best titration results (✓)

Summary

Tick (✓) the best titration results.

Using these results, the average volume of P required was ______ $\text{cm}^3$ .

Volume of Q used was ______ $\text{cm}^3$ .

12M

(b)

Q is $0.336\text{ mol / dm}^3$ sodium hydroxide, $\text{NaOH}$ .

Calculate the number of moles of sodium hydroxide in the volume of Q used.

moles of sodium hydroxide in the volume of Q used = ______

(c)

Using the equation shown and your answer to (b), deduce the number of moles of hydrochloric acid that reacted with the volume of Q used.

\text{NaOH} + \text{HCl} \rightarrow \text{NaCl} + \text{H}_2\text{O}

moles of hydrochloric acid that reacted with the volume of Q used = ______

(d)

Using your answer to (c) and the average volume of P from the titration results, calculate the number of moles of hydrochloric acid in $250\text{ cm}^3$ of P.

moles of hydrochloric acid in $250\text{ cm}^3$ of P = ______

(e)

Calculate the number of moles of hydrochloric acid in $250\text{ cm}^3$ of $0.500\text{ mol / dm}^3$ hydrochloric acid.

moles of hydrochloric acid in $250\text{ cm}^3$ of $0.500\text{ mol / dm}^3$ hydrochloric acid = ______

(f)

Using your answers from (d) and (e), calculate the number of moles of hydrochloric acid that reacted with the calcium carbonate in the tablets.

moles of hydrochloric acid that reacted with calcium carbonate = ______

(g)

Using your answer to (f), calculate the mass of calcium carbonate in one tablet of the antacid.

The relative formula mass of calcium carbonate is 100.

mass of calcium carbonate in one tablet of the antacid = ______ $\text{g}$

The rest of this paper

1 more questions

Q2Qualitative Analysis · Experimental Contexts · Observations and Measurements · Analysis, Conclusions and Evaluation21M

Loading the full paper…