Procedure: -
All absorbed moisture was removed from the crucible by heating over a Bunsen burner and then by cooling in a dessicator. The crucible was then weighed and approximately 3g of Hydrated Barium Chloride was added to the crucible (this was done wearing gloves and in a fume cupboard). The crucible and contents was then weighed on a balance. The crucible was then heated for 15 minutes using a Bunsen burner and tripod stand, with the lid partially covering the contents. The crucible was allowed to cool before being transferred to a dessicator using tongs. Once cooled, the crucible was reweighed. This process was repeated, heating for about 4 minutes each time, until two successive balance reading were within 0.002g of each other, at this point the contents were at constant mass, and all of the water had been removed.
Hazcon:-
Wear eye Protection and if any chemical splashes n your skin wash it off immediately.
Barium Chloride is harmful by inhalation and by ingestion or skin contact. Wear Gloves.
Hydrated Barium Chloride is crystalline, but the anhydrous salt that is produced is powdery. Avoid raising a dust.
Result:-
BaCl2.H2O BaCl2 + H2O
The hydrated Barium Chloride sample contained about 2.23mol of water molecules per mole.
BaCl2.H2O BaCl2 + H2O
The hydrated Barium Chloride sample contained about 2.05 mol of water molecules per mole.
Conclusion: - The calculated values of 2.23 and 2.05 mol of water of crystallisation were slightly higher than the actual value of 2 mol. The fact that in both attempts the final two mass readings are the same is indicative that the crucibles contents have reached constant mass, and the BaCl2 is therefore anhydrous.
Evaluation:-The slightly inaccuracy of the experiment could be attributed to soot forming on the crucible, this was minimised by using a blue flame from the Bunsen burner, which is less sooty than a yellow flame. If soot formed on the crucible its mess would be changed, making the results inaccurate.
Dirt could have been transferred from the tongs to the crucible while it was being lifted, again this would affect the mass of the crucible. This error would have been eliminated had clean tongs been used.
The Barium Chloride had to be heated to constant mass to ensure that all traces of water had been removed to reduce errors in the calculation. Gravimetric analysis is more accurate than volumetric analysis because the only error in gravimetry should be weighing error so the results are as accurate as the balance used.
Improvements could have been made by using a more accurate balance and also by calibrating the balance.
