Chemistry 5070/31 — 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 · Experimental Contexts · Use of Techniques, Apparatus and Materials · Analysis, Conclusions and Evaluation · Qualitative Analysis

Q117MExperimental ContextsObservations and MeasurementsUse of Techniques, Apparatus and MaterialsAnalysis, Conclusions and EvaluationFree sample

P is an aqueous solution prepared by reacting a metal oxide, $\text{MO}$ , with an excess of hydrochloric acid, $\text{HCl}$ . In preparing P, $3.36\text{ g}$ of the metal oxide was completely reacted in $1.00\text{ dm}^3$ of $0.200\text{ mol / dm}^3$ hydrochloric acid, an excess.

\text{MO} + 2\text{HCl} \rightarrow \text{MCl}_2 + \text{H}_2\text{O}

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

Q is $0.0640\text{ mol / dm}^3$ 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 $0.0640\text{ mol / dm}^3$ sodium hydroxide, $\text{NaOH}$ .

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

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

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

(c)

Before reaction with the metal oxide, $1.00\text{ dm}^3$ of the acid contained $0.200\text{ moles}$ of hydrochloric acid. Using your answer from (b), calculate the number of moles of acid that reacted with $3.36\text{ g}$ of the metal oxide, $\text{MO}$ .

moles of hydrochloric acid that reacted with the metal oxide = ______

(d)

Using your answer to (c), deduce the number of moles of metal oxide, $\text{MO}$ , that reacted with the hydrochloric acid.

moles of metal oxide that reacted with the hydrochloric acid = ______

(e)

Using your answer to (d) and the mass of metal oxide, $3.36\text{ g}$ , calculate the relative atomic mass of the metal $\text{M}$ in the metal oxide, $\text{MO}$ .
[Relative atomic mass of oxygen, $\text{O}$ , is $16$ .]

relative atomic mass of $\text{M}$ = ______

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