Chemistry 5070/32 — October/November 2020

Put P into the burette.

Pipette $25.0\text{ cm}^3$ of Q into a flask and titrate with P using three drops of thymolphthalein as the indicator.

The end-point is when the solution remains colourless for 30 seconds.

Record your results in the table.

Repeat the titration as many times as necessary to achieve consistent results.

Results

Burette readings

Summary

Tick (✓) the best titration results in the table.

Using the best titration results the average volume of P required is ______ $\text{cm}^3$.

Q is $0.100\text{ mol / dm}^3\text{ NaOH(aq)}$.

Calculate the number of moles of $\text{NaOH}$ in $25.0\text{ cm}^3$ of Q.

Give your answer to three significant figures.

number of moles of $\text{NaOH}$ in $25\text{ cm}^3$ of Q = ______

Use your answer from (b) to calculate the number of moles of $\text{H}_3\text{X}$ in the average volume of P used.

$$3\text{NaOH} + \text{H}_3\text{X} \rightarrow \text{Na}_3\text{X} + 3\text{H}_2\text{O}$$

number of moles of $\text{H}_3\text{X}$ = ______

Use your answers from (a) and (c) to calculate the concentration of $\text{H}_3\text{X(aq)}$ in P in $\text{mol / dm}^3$.

concentration of $\text{H}_3\text{X(aq)}$ = ______ $\text{mol / dm}^3$

Use your answer from (d) to calculate the mass of $\text{H}_3\text{X}$ in $200\text{ cm}^3\text{ P}$.

[$M_r$: $\text{H}_3\text{X}$, 192]

mass of $\text{H}_3\text{X}$ = ______ $\text{g}$