Question

The number of molecules present in 200 g of $N_2{O}_5$ is __________.

• A. $1.43\times {10}^{24}$
• B. $1.11\times {10}^{24}$
• C. $1.01\times {10}^{28}$
• D. $1.11\times {10}^{27}$

Answer 1

The correct option is B $1.11\times {10}^{24}$

Given mass of $N_2{O}_5$ = 200 g
Avogadro's number = $6.022\times {10}^{23}$

Gram molecular mass of $N_2{O}_5$ = (2$\times$ gram atomic mass of nitrogen) + (5$\times$ gram atomic mass of oxygen)
= 2 $\times$ 14 + 5 $\times$ 16 = 108 g

$No.ofmoles=\frac{Givenmass}{Grammolecularmass}$

Number of moles in 200 g of $N_2{O}_5$ = 200/108 = 1.85 moles.

Number of molecules present in 1 mole of $N_2{O}_5$ = $6.022\times {10}^{23}$

So, the number of molecules present in 1.85 moles = 1.85 $\times$ 6.022 $\times {10}^{23}$ = 1.11 $\times {10}^{24}$.