Question

$500ml$ of ${NH}_3$ contains $6.00\times {10}^{23}$ molecules at S.T.P. How many molecules are present in $100ml$ of ${CO}_2$ at S.T.P?

• A. $6\times {10}^{23}$
• B. $1.5\times {10}^{23}$
• C. $1.2\times {10}^{23}$
• D. None of these

Answer 1

Answer: (C)

$1.2\times {10}^{23}$

$\frac{P{V}_1}{n_{1}RT}=\frac{P{V}_2}{n_{2}RT}$ or $\frac{V_1}{n_1}=\frac{V_2}{n_2}$
$\frac{500}{1}=\frac{100}{n_2}$
$n_2=1/5$
[$6.00\times {10}^{23}$ molecules of ${NH}_3=1$ mole]
$1$ mole of ${CO}_2$ contains $6.0\times {10}^{23}$ molecules
$\therefore$ $1/5$ mole of ${CO}_2$ contains $1.2\times {10}^{23}$ molecules