Precipitation of barium sulfate?? We had to determine the content of sulfate found in lawn food for a class prac. Anyway what we did was to dissolve the fertilizer in HCl and then add barium cholride to it in order to precipitate sulfate as barium sulfate. We later determined its concentration using gravimetric analysis. The results of my group was substantially different to the actual amount of sulfate present in the fertilizer. Our result was about 2% less than the actual value. Now I am trying to find some possible sources of error in the prac. I know that we spilled a couple of drops of the mixture but it was not that much. I was wondering if somehow impurities can impact upon the mass being less than it's supposed to be? I know impurities usually cause mass to be larger but I read somewhere that occulsions can causesul mass to be smaller than the actual value? Is this true?