Expert: Dr. Henry Boyter, Jr. - 3/16/2006

Question
Hello,

I am having trouble understanding how to calculate Gravitmetric Factors. For example:

An impure sample of CaSo4.2H20 was analyzed by gravimetric analysis of calcium. A 0.5449g sample was dissolved in water and the calcium was precipitated and weighed as Ca3(PO4)2. a 0.2735g precipiate was obtained. Calculte and GF to concert Ca3(PO4)2 to Calcium and the GF to concert Ca3(PO4)2 to CaSO4.

Thank You.

P.S This is not a HW question, since we got no school here right now in Ontario because of a strike .

Answer
GF is equal to the

MolWt of species 1 divided by MolWt of species 2 (or atomic weights)

so one GF of the Ca3(PO4)2 is
molwt of Ca3(PO4)2 / atwt of Ca

GFs are usually the compound over the element (so the number is greater than 1)

so Ca3(PO4)2 has a Ca GF, Ca(SO4) has a Ca GF, etc.

So you have the amount of Ca3(PO4)2 so to go to Ca you divide by that GF, to go to Ca(SO4) you multiply that Ca answer by that GF.