Chemistry
posted by John on .
Why is my actual percent of sulfate in alum a lot less than my theoretical percent of sulfate in alum?
Actual Percent SO4= 1.68%
Theoretical Percent SO4= 40.5%

I don't know without seeing all of your work. One possibility is that you lost some of the BaSO4 ppt. A second possibility is that you didn't ppt all of the sulfate in the sample due to the conditions; i.e., pH not right, not adding enough BaCl2, etc. Your calculations could be wrong.

Well the questions are confusing, the first question asks to find the mass of sulfate in my 1 gram sample of alum based off of the mass of BaSO4 (0.52g).
The second question then asks to calculate the percent sulfate in my alum, and I don't know if that means my sample of alum or the total mass of alum the reaction produced which was 11.28. 
I think the first question is % SO4 in your 1 grams sample.
That is 0.52 x (molar mass SO4/molar mass BaSO4)*100 = about 21% (The mass is about 0.21g)
I think the second question is to calculate the theoretical percent SO4 in your 1 g sample (or any mass sample) so you can compare your experimental value with the theoretical value.
The theoretical % SO4 in alum is about 40%. (96.064*2/474.39)*100 = ? 
That sounds right to me..thanks for all of your help.