# Hydrogen and oxygen combine in the ratio of 1:8 by mass to form water.

Question.
Hydrogen and oxygen combine in the ratio of 1:8 by mass to form water. What mass of oxygen gas would be required to react completely with 3 g of hydrogen gas?

Solution:
It is given that the ratio of hydrogen and oxygen by mass to form water is $1: 8$.
Then, the mass of oxygen gas required to react completely with $1 \mathrm{~g}$ of hydrogen gas is $8 \mathrm{~g}$.
Therefore, the mass of oxygen gas required to react completely with $3 \mathrm{~g}$ of hydrogen gas is $8 \times 3 \mathrm{~g}=24 \mathrm{~g}$.