Question

Cyclopropane and oxygen at partial pressures 170 torr and 570 torr are mixed in a gas cylinder. What is the ratio of the number of moles of cyclopropane to the number of moles of oxygen?

• A. $\frac{170\times42}{570\times32}=0.39$
• B. $\frac{170}{42}\Bigg/\Bigg(\frac{170}{42}+\frac{570}{32}\Bigg)\approx0.19$
• C. $\frac{170}{740}=0.23$
• D. $\frac{170}{570}=0.30$

Answer 1

Answer: (D)

$\frac{170}{570}=0.30$

Answer 2

According to ideal gas equation,
$\, \, \, \, \, \, \, \, \, \, \, p_1 V=n_1 RT \, \, \, \, \, \, \, \, \, \, \, ...(i)$
$\, \, \, \, \, \, \, \, \, \, \, p_2 V=n_2 RT \, \, \, \, \, \, \, \, \, \, \, ...(ii)$
From Eqs. (i) and (ii)
$\frac{p_1 V}{p_2 V}=\frac{n_1\, RT}{n_2\, RT} \, \, \, \Rightarrow \frac{p_1}{p_2}=\frac{n_1}{n_2}$
$\frac{n_1}{n_2}=\frac{p_1}{p_2}=\frac{170}{570}=0.30$