How to calculate percentage composition?

How do you calculate the percentage of an element in something?

for example....



hydrogen in NaH2PO4



hydrogen in CaSO4



Oxygen in NH4H2PO4



Oxygen in (CH3)2COHow to calculate percentage composition?
All numbers are in 3 sig figures.

Molar masses



NaH2PO4 = 120

CaSO4 = 136

NH4H2PO4 = 115

(CH3)2CO = 58.1



Molar Mass of Hydrogen in NaH2PO4 : 2

2/120*100 = 1.666...%



Molar mass of Hydrogen in CaSO4 : 0 (because there's no hydrogen)

0/136*100 = 0%



Molar mass of Oxygen in NH4H2PO4 : 64

64/115*100 = 55.7%



Molar mass of Oxygen in (CH3)2CO : 16.0

16/58.1*100 = 27.5%How to calculate percentage composition?
it's not too difficult



hydrogen in NaH2PO4

you have to calculate the atomic weight of the whole compound



23 + 2 + 31 + 4 x (16) = 120 (atomic weight of the compound)



then

there are two atoms of hydrogen in that compund so

the atomic weight of hydrogen is : 2 x 1 = 2.

so



% H = 2 x 100/120

= 200/120 = 1.6 % of hydrogen in NaH2PO4.