Chemistry 5070/31 — October/November 2022

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

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

Q117MObservations and MeasurementsExperimental ContextsAnalysis, Conclusions and EvaluationFree sample

P is a sample of dilute sulfuric acid.

P is prepared by adding $5.0\text{ cm}^3$ of concentrated sulfuric acid to distilled water and making the total volume of the solution up to $250\text{ cm}^3$ with distilled water.

Q is $0.360\text{ mol / dm}^3$ sodium carbonate.

(a)

Put P into the burette.

Pipette $25.0\text{ cm}^3$ of Q into a flask and titrate with P using methyl orange indicator.

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 ( $\checkmark$ )

Summary

Tick ( $\checkmark$ ) the best titration results.

Using the best titration results the average volume of P required is ______ $\text{cm}^3$ .

12M

(b)

Q is $0.360\text{ mol / dm}^3$ sodium carbonate.

The equation for the reaction is shown.

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

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

Give your answer to three significant figures.

concentration = ______ $\text{mol / dm}^3$

(c)

P is prepared by adding $5.0\text{ cm}^3$ of concentrated sulfuric acid to distilled water and making the total volume of the solution up to $250\text{ cm}^3$ with distilled water.

Use your answer from (b) to calculate the number of moles of sulfuric acid in $5.0\text{ cm}^3$ of concentrated sulfuric acid.

______ $\text{mol}$

(d)

Use your answer from (c) to calculate the concentration, in $\text{mol / dm}^3$ , of concentrated sulfuric acid.

concentration = ______ $\text{mol / dm}^3$

(e)

Use your answer from (d) to calculate the mass, in $\text{g}$ , of sulfuric acid, $\text{H}_2\text{SO}_4$ , in $1\text{ dm}^3$ of concentrated sulfuric acid.

[ $M_r$ : $\text{H}_2\text{SO}_4$ , 98]

mass = ______ $\text{g}$

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Q2Qualitative Analysis · Experimental Contexts · Analysis, Conclusions and Evaluation · Observations and Measurements23M

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