Chemistry 5070/32 — October/November 2017

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

The composition of concentrated sulfuric acid can be determined by diluting a sample of the acid and then titrating aqueous sodium hydroxide of known concentration with the diluted acid.

P is dilute sulfuric acid. It has been prepared by adding $10.0\text{ cm}^3$ of the concentrated sulfuric acid to distilled water and then making the total volume of the solution up to $500\text{ cm}^3$ in a volumetric flask by adding distilled water.

Q is $0.586\text{ mol / dm}^3$ sodium hydroxide.

(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 the best titration results, the average volume of P required was ______ $\text{cm}^3$ .

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

12M

(b)

Q is $0.586\text{ mol / dm}^3$ sodium hydroxide.

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

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)

Using your answer from (b), calculate the number of moles of sulfuric acid in $10.0\text{ cm}^3$ of concentrated sulfuric acid.

moles of sulfuric acid in $10.0\text{ cm}^3$ of concentrated sulfuric acid = ______

(d)

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

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

(e)

Using your answer from (d), calculate the mass, in $\text{g}$ , of sulfuric acid in $1\text{ dm}^3$ of concentrated sulfuric acid.
[The relative formula mass of sulfuric acid is 98.]

mass of sulfuric acid in $1\text{ dm}^3$ of concentrated sulfuric acid = ______ $\text{g}$

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