TEST OF PRACTICAL KNOWLEDGE QUESTION
All your burette readings (initial and final), as well as the size of your pipette, must be recorded but no account of experimental procedure is required. All calculations must be done in your answer book. A is a solution of HCl containing 7.30g dm\(^{-3}\), B is a solution of X\(_2\)CO\(_{3}\) containing 10.6 gdm\(^{-3}\)
(i) Put A into your burette and titrate readings against 20.0 cm\(^3\) or 25.0cm\(^3\) portions of B using methyl orange as indicator. Tabulate your burette reading and calculate the average volume of A used. The equation for the reaction involved in the titration is ;
X\(_2\)CO\(_{3(aq)}\) + 2HCl\(_{(aq)}\) \(\to\) 2XCl\(_{(aq)}\) + H\(_2\)O\(_{(l)}\) + CO\(_{2(g)}\)
(ii) From your results and the information provided above, calculate the (i) concentration or A in mol dm\(^{3-}\)
(i) Tabulating the burette readings
The burette readings (initial and final for at least three titrations) depend on the actual titration you perform in the laboratory, so a specimen table is shown. The rough titre is discarded and the concordant titres (within 0.10 cm3) are averaged.
| Burette reading (cm3) | Rough | 1st | 2nd |
|---|
| Final reading | 25.10 | 24.60 | 24.50 |
| Initial reading | 0.00 | 0.00 | 0.00 |
| Volume of A used | 25.10 | 24.60 | 24.50 |
Average volume of A (concordant titres only): \(\dfrac{24.60 + 24.50}{2} = 24.55\ \text{cm}^3\) (specimen value).
(ii)(i) Concentration of A in mol dm-3
This value does not depend on the titre; it is obtained directly from the mass concentration given.
Molar mass of HCl \(= 1.00 + 35.5 = 36.5\ \text{g mol}^{-1}\).
\[ \text{Concentration of A} = \frac{\text{mass concentration}}{\text{molar mass}} = \frac{7.30}{36.5} = 0.200\ \text{mol dm}^{-3} \]
Therefore the concentration of A (HCl) \(= 0.200\ \text{mol dm}^{-3}\).
(i) Tabulating the burette readings
The burette readings (initial and final for at least three titrations) depend on the actual titration you perform in the laboratory, so a specimen table is shown. The rough titre is discarded and the concordant titres (within 0.10 cm3) are averaged.
| Burette reading (cm3) | Rough | 1st | 2nd |
|---|
| Final reading | 25.10 | 24.60 | 24.50 |
| Initial reading | 0.00 | 0.00 | 0.00 |
| Volume of A used | 25.10 | 24.60 | 24.50 |
Average volume of A (concordant titres only): \(\dfrac{24.60 + 24.50}{2} = 24.55\ \text{cm}^3\) (specimen value).
(ii)(i) Concentration of A in mol dm-3
This value does not depend on the titre; it is obtained directly from the mass concentration given.
Molar mass of HCl \(= 1.00 + 35.5 = 36.5\ \text{g mol}^{-1}\).
\[ \text{Concentration of A} = \frac{\text{mass concentration}}{\text{molar mass}} = \frac{7.30}{36.5} = 0.200\ \text{mol dm}^{-3} \]
Therefore the concentration of A (HCl) \(= 0.200\ \text{mol dm}^{-3}\).
