Chemistry 5070/31 — May/June 2012

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

questions

marks

minutes

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

Q118MExperimental ContextsUse of Techniques, Apparatus and MaterialsObservations and MeasurementsAnalysis, Conclusions and EvaluationFree sample

Ethanedioic acid, $\text{H}_2\text{C}_2\text{O}_4$ , forms crystals which are hydrated and have the formula $\text{H}_2\text{C}_2\text{O}_4 \cdot x\text{H}_2\text{O}$ .

P is a solution containing $9.45\text{ g}$ of $\text{H}_2\text{C}_2\text{O}_4 \cdot x\text{H}_2\text{O}$ in $1.00\text{ dm}^3$ of solution.
Q is $0.150\text{ mol / dm}^3$ sodium hydroxide, $\text{NaOH}$ .

You are to determine the value of $x$ in the formula $\text{H}_2\text{C}_2\text{O}_4 \cdot x\text{H}_2\text{O}$ by titrating Q with P.

(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 $0.150\text{ mol / dm}^3$ sodium hydroxide.
Using your results from (a), calculate the concentration, in $\text{mol / dm}^3$ , of the ethanedioic acid, $\text{H}_2\text{C}_2\text{O}_4$ , in P.

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

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

(c)

Using your answer from (b), calculate the concentration, in $\text{g / dm}^3$ , of ethanedioic acid, $\text{H}_2\text{C}_2\text{O}_4$ , in P.
[The relative formula mass of ethanedioic acid is 90.]

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

(d)

Using your answer from (c), calculate the mass of water in $9.45\text{ g}$ of hydrated ethanedioic acid, $\text{H}_2\text{C}_2\text{O}_4 \cdot x\text{H}_2\text{O}$ .

mass of water = ______ $\text{g}$

(e)

Calculate the value of $x$ in the formula $\text{H}_2\text{C}_2\text{O}_4 \cdot x\text{H}_2\text{O}$ .
[The relative formula mass of $\text{H}_2\text{O}$ is 18.]

value of $x$ = ______

The rest of this paper

1 more questions

Q2Experimental Contexts · Qualitative Analysis22M

Loading the full paper…