40 gms each of the methane and oxygen are mixed in an empty container maintained at 40°C. The fraction of the total pressure exerted by oxygen is_________________?

Question

Accepted Answer

1/3. According to Dalton's Law of Partial Pressures, the partial pressure is proportional to the moles. Since both gases have equal masses (40g) and their molar masses are different ($	ext{CH}_4=16 	ext{ g/mol}$, $	ext{O}_2=32 	ext{ g/mol}$), the mole ratio is $40/16 : 40/32 = 2.5 : 1.25$, or $2:1$. The fraction for oxygen is $1.25 / (2.5 + 1.25) = 1.25 / 3.75 = 1/3$.