Question

$A,B$ and $C$ are three cylinders of volume 11.2 L each. $H_2,O_2$ and $N_2$ gases at STP are filled in $A,B$ and $C$ respectively.
(a) Find the number of moles of $H_2$ molecules in $A$.
(b) Calculate the number of molecules of $O_2$ present in $B.\left(c\right)Ifthevolumeof$N$,presentin$C$isdoubledatSTP,calculatethemassingramof$N_2$gas.[given:MolarvolumeatSTP$= 22.4$L,At.mass:$H = 1,\ O= 16,\ N = 14$]

Answer 1

The volume of one mole of any gas at STP is $22.4$ L and there are $6.022\times {10}^{23}$ molecules in it.
(a) The volume of $H_2$ at STP in cylinder $A$ is $11.2$ L
$\therefore$ The number of moles in $11.2$ L $=\frac{11.2}{22.4}=0.5$
The number of $H_2$ molecules $=0.5\times 6.022\times {10}^{23}$
(b) The number of moles of $O_2$ molecules in 11.2 L $=0.5\times 6.022\times {10}^{23}=3.011\times {10}^{23}$
(c) The number of moles of $N_2$ in $11.2$ L $=\frac{11.2}{22.4}=0.5$
Mass of $1$ mole of $N_2=28g$
$\therefore$ Mass of $0.5$ moles of $N_2=14g$
If the volume of $N_2$ at STP is doubled, it becomes $22.4$ L. It means $1$ mole of $N_2$.
Therefore, the mass of $N_2$ in grams when the volume is $22.4$ L is $28$ g.