Question

$100$ mL of any gas at NTP was heated with $Sn$. $Sn$ got converted into stannous sulphide and hydrogen was left. This hydrogen when passed over hot $CuO$ produced $0.081$ g of water. If the vapour density of the gas is $17$, then the number of atoms it contains in its formula is :

Answer 1

Since tin is converted into sulphide and hydrogen is left, this gas contains H and S say $H_a{S}_b$
$H_a{S}_b+bSn\to bSnS+\left(\frac{a}{2}\right)H_2\stackrel{CuO}{\to }\left(\frac{a}{2}\right)H_2$
The reaction suggests that
$\because$ Mole of $H_2$ formed = mole of $H_{2}O$ formed
and Mole of $H_a{S}_b=\left(a/2\right)$ mole of $H_2$
$=\left(a/2\right)$ mole of $H_{2}O$
$\therefore \frac{100}{22400}=\frac{a}{2}\times \frac{0.081}{18}$
$\therefore a=2$
$\because$ Molar mass of $H_a{S}_b=V.D\times 2=17\times 2=34$
$\therefore 1\times a+32\times b=34$
$1\times 2+32\times b=34$
$b=1$
Thus, the gas is $H_{2}S$
and it contains $2H+1S=3$ atoms in its formula.