Calculated the mass of the dried precipitate. The mass of the crucible with dried precipitate, minus the mass of the crucible: 0.860g
Calculated the number if moles of precipitate:
Given the 1:1 ratio, there are also 0.00368 moles of sulfate ions in the precipitate.
Calculated the mass of the sulfate ions in the precipitate:
Calculated the theoretical percentage of sulfate content in the unknown sulfate sample:
Compared the properties of various sulfates of alkali and alkali earth metals, with the properties of the unknown sulfate:
The closest of these to the unknown sulfate is:
Calculated the percent error:
As such, we can conclude that the most likely molecular formula for the unknown sulfate is:
The goal of this experiment is to determine the molecular formula of an unknown alkali (or alkali earth) metal sulfate, via application of gravimetric analysis. This possible by the use of barium nitrate, due to the very low solubility of barium sulfate. All of the sulfate ions within the HCl solution reacts with the barium (which is added to excess, to ensure that all of the sulfate reacts), the solution is filtered (with ashless filter paper), rinsed thoroughly, the paper burnt to isolate the precipitate, and then the mass of the precipitate is measured.
Given the data gathered, and knowledge of the molar mass of barium sulfate (and its constituent ions) it is possible to calculate the mass of the sulfate, and from that, the percentage of sulfate within the unknown alkali (or alkali earth) metal sulfate.
The most likely molecular formula for the unknown sulfate is:
Percent error: 0.961%
Possible sources of error include:
- Incomplete precipitation (would result in lower experimental sulfate content than expected)
- Incomplete transfer of precipitate from the beaker to the funnel (would also result in lower experimental sulfate content than expected)
- Incomplete washing of the precipitate, and/or incomplete drying of the precipitate (would result in higher experimental sulfate content than expected)
- Failure to rinse the thermometer and beaker (would cause a lower experimental sulfate content, due to loss of precipitate)
- Human error is always in effect, given that the laboratory does not function under ideal conditions. As such, there is always the possibility of inaccuracies with measurement, perception of measurement, inaccuracies of equipment, and other such errors. (However, this is not likely to be the sole cause of the inaccuracies within this experiment, though it may contribute to it.)
A possible improvement to make to subsequent iterations of this experiment would be to carry out the entire experiment in a single session, and not divide it over two subsequent weekends. This reduces the possibility of human error, and the possibility that external factors can disrupt the solution.