[sciencenerd]

we mixed zinc sulfate heptahydrate adn calcium acetate monohydrate to get calcium sulfate, zinc acetate, and water...but when we measure the mass of the precipate (calcium sulfate) it is very low and the percent error is huge..why is that?

[cliverlong]

we mixed zinc sulfate heptahydrate adn calcium acetate monohydrate to get calcium sulfate, zinc acetate, and water...but when we measure the mass of the precipate (calcium sulfate) it is very low and the percent error is huge..why is that?

How about a balanced chemical equation, some data and calculations?

Calcium sulphate exists in different hydrated forms
http://en.wikipedia.org/wiki/Calcium_sulfate#Dehydration_reactions

Different sources give contradictory statements about the solubility of calcium sulphate

http://answers.yahoo.com/question/index?qid=20080206193419AAIRRC1
http://www.chemguide.co.uk/inorganic/group2/solubility.html
http://www.csudh.edu/oliver/chemdata/data-ksp.htm

If you took K_sp to be 10^-6 would this fit your data and calculations about the yield?

Maybe calcium sulphate coexists in various forms as a result of your reaction and some forms a precipitate until concentration drops and some remains in solution?

Clive