What is the percent composition of oxygen in the compound?
The percentage composition of oxygen in water can be calculated by dividing the mass of oxygen by the mass of water. 1 mole of water (which weighs 18.0153 g) contains 15.9994 gm of oxygen, hence the percentage composition of oxygen is:
% composition of oxygen in water = mass of oxygen / mass of water x 100
= `(15.9994)/(18.0153) xx 100 = 88.8101 %`
Thus water contains 88.8101% (or can be rounded off to 88.8%) oxygen.
We can similarly calculate the % composition of hydrogen in water, which is:
% composition of hydrogen in water = `(2.01588)/(18.0153) xx 100 = 11.1898 %`
This can also be calculated as 100%- % composition of oxygen ( = 100 - 88.8101 = 11.1899%), since oxygen and hydrogen together constitute water and hence their respective % compositions must add to 100% .
Hope this helps.