How many formula units are in 12.5 moles of calcium phosphate?

A formula unit is to an ionic compound as an atom is to an element. That is, for calcium phosphate, one formula unit contains 3 atoms of calcium and 2 ions of phosphate PO4, as shown in the chemical formula Ca3 (PO4) 2. To determine the number of formula units given the moles, we multiply the number of moles by Avogadro's number:

12.5 moles * (6.02x10^23 formula units/mole) = 7.525 x 10^24 formula units