gravimetric anaylsis help needed please

[Zahta]

Hey guys i need some help with a question on gravimetric analysis 


If you analysed a commerical fetilliser how does the result for the percentage of sulphur (as sulfate) present agree with your manufactures specification? try to account for any differences.The manufactures specification is
17.0%   and  my  precentage of sulphur is 15.0%

[mihir94]

Here are some errors that can lead to an underestimation:

1) Not enough of the precipitate forming chemical added- not enough of the precipitate will form as some of the ions (in this case sulfate) that are being analysed for will remain in solution.

2) Forming a precipitate that is too soluble- All ions have a certain degree of solubility. Resulting in loss of some analyte ions.

3) Rinsing the precipitate with a lot of water- too much water or solvent could cause some of the precipitate to redissolve.

Hope that helps