Question

$112.0$ mL of ${NO}_2$ at STP was liquefied, the density of the liquid being $1.15$ $g{mL}^{-1}$. Calculate the volume and the number of molecules in the liquid ${NO}_2$.

(Atomic weight of $N=14$ amu)

• A. $0.10$ mL and $3.01\times {10}^{22}$
• B. $0.20$ mL and $3.01\times {10}^{21}$
• C. $0.20$ mL and $6.02\times {10}^{23}$
• D. $0.40$ mL and $6.02\times {10}^{21}$

Answer 1

The correct option is B $0.20$ mL and $3.01\times {10}^{21}$

Moles of ${NO}_2=\frac{112}{22400}=5\times {10}^{-3}mol$

Mass of ${NO}_2=5\times {10}^{-3}\times 46g=0.23g$

Volume of ${NO}_2=\frac{Mass}{Density}=\frac{0.23}{1.15}=0.2mL$

Number of molecule $=5\times {10}^{-3}\times 6.023\times {10}^{23}=3.1\times {10}^{21}$.