Question

The volume of a gas at ${21}^{o}C$ temperature and $71.8cm$ pressure is $1L$. If the density of the gas is $1.2g/L$ at NTP, then its mass will be

• A. $4g$
• B. $4.21g$
• C. $1.13g$
• D. $10g$

Answer 1

The correct option is C $1.13g$

We know that the gas follows Ideal gas law, which states

$\frac{P}{\rho T}=\text{constant}$ or

$\frac{P_1}{{\rho }_1{T}_1}=\frac{P_2}{{\rho }_2{T}_2}$

Given that Density at NTP is ${\rho }_2=1.2g/L$

$T_2={20}^{o}C=293.15K$ and $P_2=76$ cm of Hg

We have $T_1={21}^{o}C=294.15K$ and $P_1=71.8$ cm of Hg

Thus ${\rho }_1={\rho }_2\times \frac{T_2}{T_1}\times \frac{P_1}{P_2}=1.2\times \frac{293.15}{294.15}\times \frac{71.8}{76}=1.13g/L$

Thus mass of the gas = ${\rho }_2\times V_2=1.13g/L\times 1L=1.13g$