How many moles are in 30 grams of H3PO4?

Mass = Moles x GFM

mass = 30g so;

30 = mol x GFM

To calculate the GFM, you require a data booklet or similar.

Mine tells me that the GFMs are:

H: 1 H₃ so 3 x 1 = 3

P: 31 P so 1 x 31 = 31

O:16 O₄ so 4 x 16 = 64

GFM = 64 + 31 + 3 = 98

30 = 98 x mol

mol = 30 / 98

mol = 0.31 mol