Mg3(PO4)2 - the molar mass would be 262g/mol, which is 100%
Atomic mass of Mg is 24, since we have 3Mg we multiply by 3 and get a mass of 72
262 : 100% = 72 : x%
x = 72*100 / 262
x = 27.5%
And do that for every element — get the molar mass of P and multiply by 2, use a ratio, and get the molar mass of O and multiply by 8 and use ratios :)
Negative because it'll have to gain an electron
The formula for mole is
n= Mass/Mol mass
Mol Mass: S=32
O2= 16(2)
—————
64 g/mol
N= 17.50 g
————— (cancel both g)
64 g/mol
= 0.27 mol is the answer