Determine the number of moles of compound in each of the following samples.?

4.50g H2O

471.6g Ba (OH) 2

129.68g Fe3 (PO4) 2

For the answer to the question above, we have to use this formula

moles equal mass divided by the molar mass

a) 4.50 g divided by the molar mass of water

molar mass of water = 2x1.0 + 1x16.0 = 18

4.50 g / 18.0 g per mole = 0.25 moles

b) 471.6 g / Molar mass of Ba (OH) 2 = moles

c) 129.68 g / molar mass of Fe3 (PO4) 2 = moles

atoms of P in Mg3 (PO4) 2

2 atoms of P in each molecule of Mg3 (PO4) 2

247 g / molar mass of Mg3 (PO4) 2 = moles

moles of Mg3 (PO4) 2 x 6.022x10^23 = molecules of Mg3 (PO4) 2

I hope my answers gave you clarity on your question.