Question

A flask of methane $\left(C{H}_4\right)$ was weighed. Methane was then pushed out and the flask again weighed when filled with oxygen at the same temperature and pressure. The mass of oxygen would be :

• A. the same as the methane
• B. half of the methane
• C. double of that of methane
• D. negligible in comparison to that of methane

Answer 1

Answer: (C)

double of that of methane

Avogadro's Law : It states "equal volumes of any two gases at the same temperature and pressure contain the same number of molecules". (same no of moles)

So both have same no of moles in flask,

$n_1=n_2$

$\frac{{\omega }_{C{H}_4}}{M_{C{H}_4}}=\frac{{\omega }_{O_2}}{M_{O_2}}$

$\frac{{\omega }_{O_2}}{{\omega }_{C{H}_4}}=\frac{M_{O_2}}{M_{C{H}_4}}=\frac{32}{16}=2$

So mass of oxygen would be double of that of methane.