Question

A glass tube of volume 112 ml containing a gas is partially evacuated till the pressure in it drops to $3.8\times {10}^{-5}$ torr at $0^{0}C$. The number of molecules of the gas remaining in the tube is

• A. 3 X 10¹⁷
• B. 1.5 X 10¹⁴
• C. 4.5 X 10¹⁸
• D. 1.5 X 10¹⁹

Answer 1

The correct option is B

1.5 X 10¹⁴

PV=nRT
$n=\frac{PV}{RT}=\frac{3.8\times {10}^{-5}\times 0.00131579\times 112\times {10}^{-3}}{.082\times 273}$

Since 1 atm is 0.00131579 torr
$=1.89\times {10}^{-8}mol$
No. of molecules = $0.02461\times {10}^{-8}mol$
$=1.5\times {10}^{14}$