Question

What is the composition of water (ratio of hydrogen to oxygen) (i) by volume (ii) by mass

Answer 1

By volume

• Two hydrogen atoms and one oxygen atom combine to form water (H₂O), thus volume ratio of hydrogen to oxygen is 2:1.

By mass

• The atomic mass of hydrogen is one and the atomic mass of oxygen is 16.
• Since we have two hydrogens, the mass of hydrogen becomes 2×1=2; whereas the mass of oxygen remains 16, since there is only one oxygen atom in H₂O.
• Thus its ratio by mass becomes 2:16. If simplified further, we get 1:8.