Chemistry 5070/31 — May/June 2015

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 and titrate with $\mathbf{Q}$, 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

Summary

Tick (✓) the best titration results.

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

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

$\mathbf{P}$ is $0.0984\text{ mol / dm}^3$ sodium hydroxide.

Calculate the number of moles of sodium hydroxide in the volume of $\mathbf{P}$ used.

moles of sodium hydroxide in the volume of $\mathbf{P}$ used = ______

$\mathbf{Q}$ is an aqueous solution of $\text{H}_3\text{PO}_3$ containing $5.04\text{ g / dm}^3$.

Calculate the concentration, in $\text{mol / dm}^3$, of $\text{H}_3\text{PO}_3$ in $\mathbf{Q}$.
The relative formula mass of $\text{H}_3\text{PO}_3$ is 82.

concentration of $\text{H}_3\text{PO}_3$ in $\mathbf{Q}$ = ______ $\text{mol / dm}^3$

Calculate the number of moles of $\text{H}_3\text{PO}_3$ in the average volume of $\mathbf{Q}$ used in the titration.

moles of $\text{H}_3\text{PO}_3$ = ______

Using your answers from (b) and (d), calculate the number of moles of sodium hydroxide which react with 1 mole of $\text{H}_3\text{PO}_3$.

moles of sodium hydroxide = ______

Using your answer to (e), write an equation for the reaction of the oxyacid of phosphorus, $\text{H}_3\text{PO}_3$, with sodium hydroxide.

______