Question

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

• A. $3\times {10}^{17}$
• B. $1.5\times {10}^{14}$
• C. $112.5\times {10}^{20}$
• D. Name of the gas is required

Answer 1

Answer: (C)

$112.5\times {10}^{20}$

volume = 0.112 L

pressure = 3.75 atm

temp = 273K

gas law is PV=nRT

$n=\frac{3.75\times 0.112}{0.0821\times 273}$

n=0.01874 moles

A mole has $6.022\times {10}^{23}$ atoms or molecules of the pure substance being measured

no. of molecules $=0.01874\times 6.022\times {10}^{23}=112.5\times {10}^{20}$

Hence, the correct option is $\text{C}$