A student performs a titration to find the concentration of a solution of barium hydroxide (Ba(OH)2\text{Ba(OH)}_2Ba(OH)2).
She uses this method:
(i) State what the student should do while adding the acid, to make sure that the indicator changes colour permanently.
The table shows the student's titration results.
| Titration | 1 | 2 | 3 | 4 |
|---|---|---|---|---|
| Volume of acid added in cm3\text{cm}^3cm3 | 22.35 | 21.65 | 21.85 | 21.75 |
Concordant results are volumes within 0.20 cm30.20\text{ cm}^30.20 cm3 of each other.
(ii) Identify which results are concordant.
(iii) Use the concordant results to calculate the average (mean) volume of acid added.
The table shows the titration results of another student.
| Parameter | Value |
|---|---|
| Volume of barium hydroxide used in cm3\text{cm}^3cm3 | 20.0 |
| Concentration of hydrochloric acid in mol/dm3\text{mol/dm}^3mol/dm3 | 0.0800 |
| Average volume of hydrochloric acid added from burette in cm3\text{cm}^3cm3 | 18.50 |
The equation for the reaction is:
Ba(OH)2+2HCl→BaCl2+2H2O \text{Ba(OH)}_2 + 2\text{HCl} \rightarrow \text{BaCl}_2 + 2\text{H}_2\text{O} Ba(OH)2+2HCl→BaCl2+2H2O(i) Calculate the amount, in moles, of HCl\text{HCl}HCl in 18.50 cm318.50\text{ cm}^318.50 cm3 of the hydrochloric acid.
(ii) Calculate the amount, in moles, of Ba(OH)2\text{Ba(OH)}_2Ba(OH)2 in the barium hydroxide solution.
(iii) Calculate the concentration, in mol/dm3\text{mol/dm}^3mol/dm3, of the barium hydroxide solution.
Describe how you could use the method of crystallisation to obtain a pure, dry sample of solid barium chloride from a dilute solution of barium chloride.
