Chemistry 5070/32 — May/June 2017

Put $\mathbf{Q}$ into the burette.

Pipette a $25.0\text{ cm}^3$ (or $20.0\text{ cm}^3$) portion of $\mathbf{P}$ into a flask.

Add $\mathbf{Q}$ from the burette until the red-brown colour fades to pale yellow, then add a few drops of the starch indicator. This will give a dark blue solution. Continue adding $\mathbf{Q}$ slowly from the burette until one drop of $\mathbf{Q}$ causes the blue colour to disappear, leaving a colourless solution.

Record your results in the table, repeating the titration as many times as you consider necessary to achieve consistent results.

Results

Burette readings

Summary

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

Using these results, the average volume of $\mathbf{Q}$ required was ______ $\text{cm}^3$.

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

$\mathbf{Q}$ is $0.0230\text{ mol / dm}^3$ sodium thiosulfate.

Calculate the number of moles of sodium thiosulfate in the average volume of $\mathbf{Q}$ used in the titration.

moles of sodium thiosulfate = ______

Using your answer from (b), deduce the number of moles of iodine in the volume of $\mathbf{P}$ used in the titration.

$$2\text{Na}_2\text{S}_2\text{O}_3 + \text{I}_2 \rightarrow \text{Na}_2\text{S}_4\text{O}_6 + 2\text{NaI}$$

moles of iodine = ______

Using your answer from (c), calculate the number of moles of iodine in $250\text{ cm}^3$ of $\mathbf{P}$.

moles of iodine in $250\text{ cm}^3$ of $\mathbf{P}$ = ______

Using your answer from (d), deduce the number of moles of chlorine in $50\text{ cm}^3$ of the chlorine water.

$$\text{Cl}_2 + 2\text{KI} \rightarrow 2\text{KCl} + \text{I}_2$$

moles of chlorine in $50\text{ cm}^3$ of the chlorine water = ______

Using your answer from (e), calculate the mass, in g, of chlorine in $1\text{ dm}^3$ of the chlorine water.
[$A_r$: $\text{Cl}$, 35.5]

mass of chlorine in $1\text{ dm}^3$ of the chlorine water = ______ $\text{g}$