Chemistry 5070/32 — October/November 2012

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

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Topics Observations and Measurements · Analysis, Conclusions and Evaluation · Experimental Contexts · Qualitative Analysis

Q117MObservations and MeasurementsExperimental ContextsAnalysis, Conclusions and EvaluationFree sample

P is an aqueous solution prepared by reacting a metal carbonate, $\text{MCO}_3$ , with an excess of dilute sulfuric acid, $\text{H}_2\text{SO}_4$ . In preparing P, $5.04\text{ g}$ of the metal carbonate was completely reacted in $1.00\text{ dm}^3$ of $0.100\text{ mol / dm}^3$ sulfuric acid, an excess.

\text{MCO}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{MSO}_4 + \text{H}_2\text{O} + \text{CO}_2

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

Q is $0.0800\text{ mol / dm}^3$ 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 $0.0800\text{ mol / dm}^3$ sodium hydroxide, $\text{NaOH}$ .

Using your results from (a), calculate the concentration, in $\text{mol / dm}^3$ , of sulfuric acid in P.

2\text{NaOH} + \text{H}_2\text{SO}_4 \rightarrow \text{Na}_2\text{SO}_4 + 2\text{H}_2\text{O}

concentration of sulfuric acid in P = ______ $\text{mol / dm}^3$

(c)

Before reaction with the metal carbonate, $1.00\text{ dm}^3$ of the acid contained $0.100\text{ mole}$ sulfuric acid. Using your answer from (b), calculate the number of moles of acid that reacted with $5.04\text{ g}$ of the metal carbonate, $\text{MCO}_3$ .

moles of sulfuric acid that reacted with the metal carbonate = ______

(d)

Using your answer to (c), deduce the number of moles of metal carbonate, $\text{MCO}_3$ , that reacted with the sulfuric acid.

moles of metal carbonate that reacted with the sulfuric acid = ______

(e)

Using your answer to (d) and the mass of metal carbonate, $5.04\text{ g}$ , calculate the relative atomic mass of metal M in the metal carbonate, $\text{MCO}_3$ .
[Relative formula mass of carbonate, $\text{CO}_3$ , is 60.]

relative atomic mass of M = ______

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