DRAFT: This module has unpublished changes.

Data Analysis

Table 3: Determination of the Amount of Sulfate in the Unknown

 Parameter Value Mass of the unknown sample (g) 0.3550 g Mass of the crucible and lid (g) 39.4156 g Mass of the crucible, lid and precipitate (g) 39.9819 g Mass of precipitate (g) 0.5663 g Number of moles of precipitate (mol) 2.426 x 10^-3 mol Number of moles of sulfate in precipitate (mol) 2.426 X 10^-3 mol Mass of sulfate in precipitate (g) 0.2331 g Percent of sulfate 65.66%

Table 43: Possible Unknowns

 Formula Formula Weight (g/mol) Sulfate content (%) Solubility in Water Li2SO4 109.95 g/mol 87% Yes Na2SO4 142.05 g/mol 68% Yes Na2SO4* H2O 160.066 g/mol 60% Yes K2SO4 174.27 g/mol 55% Yes CaSO4 136.15 g/mol 71% Slightly MgSO4 120.38 g/mol 80% Yes SrSO4 183.69 g/mol 52% Slightly

Calculations

1. Mass of dried precipitate

(mass of crucible with dried precipitate-mass of empty crucible = mass of dried precipitate)

39.9819 g - 39.4156 g = 0.5663 g of BaSO4

2. Number of moles in the precipitate

3. Number of moles of sulfate ions

Ba (aq) + SO4 (aq) = BaSO4 (s)

4. The mass of sulfate ions

5. Theoretical precentage of sulfate content in the unknown sample

6. Based on Table 2 above and the percent of sulfate content  the unknown is Na which makes the sulfate compound Na2SO4.

7. Calculate the percent error

Conclusion

The purpose of this lab was to use gravimetric analysis to obtain the formula of an unknown sulfate sample. This involves making the analyte into a water insoulable form which precipitates out of the solution and can be isolated by filtering and drying it. Then the mass is obtained and the number of moles and percentage of the sulfate content are able to be determined. Based on the findings of the experiment it can be determined that the unknown sulfate was Na2SO4. The percent of sulfate content in our experimental data was 65.66% and was closest to the actual sulfate content of 68% which is what it is for Na2SO4. The percent error was 3.4% which meant that the results obtained were very close to the percent of Na2SO4. Some sources of error in the experiment could have come from not heating the solution long enough and any residue left on the tongs or beakers could alter the results. If this experiment were to be performed again, more trials would be good to get a more precise result if a lot of time was given since this was a very long experiment. Also if the solution was heated for a longer time, the results might have been a little more accurate.

DRAFT: This module has unpublished changes.