Question

$500\, mL$ of $NH _{3}$ contains $6.0 \times 10^{23}$ molecules at STP. How many molecules are present in $100 \,mL$ of $CO _{2}$ at STP?

• 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)

$\frac{ PV _{1}}{ n _{1} RT } =\frac{ PV _{2}}{ n _{2} RT }$
$\frac{ V _{1}}{ n _{1}} =\frac{ V _{2}}{ n _{2}} $
$\frac{500}{1} =\frac{100}{ n _{2}} $
$n _{2} =\frac{1}{5}$
As $1 $ mole of $CO _{2}$ contains $6.0 \times 10^{23}$ molecules.
So $\frac{1}{5}$ mole of $CO _{2}$ contains $1.2 \times 10^{23}$ molecules.