Question

What is the number of oxygen atoms present in 126 g of ${HNO}_3$?

• A. $36.132\times {10}^{23}$
• B. $9.033\times {10}^{23}$
• C. $120.44\times {10}^{23}$
• D. $16.132\times {10}^{23}$

Answer 1

The correct option is A $36.132\times {10}^{23}$

Molecular mass of $HN{O}_3$ = atomic mass of hydrogen + atomic mass of nitrogen + 3$\times$ atomic mass of oxygen = 1 + 14 + (3 $\times$ 16) = 63 u.

Number of moles = $\frac{Givenmass}{Grammolecularmass}$

Moles of $HN{O}_3$ = $\frac{126}{63}$ = 2 moles

$\bullet$ In 1 molecule of $HN{O}_3$ we have 3 atoms of oxygen.

$\bullet$ 1 mole of $HN{O}_3$ contains 3 moles of oxygen atoms. So, in 2 moles of $HN{O}_3$ we will have 6 moles of oxygen atoms.

$\bullet$ One mole of a substance contains $6.022\times {10}^{23}$ particles. So, the number of atoms in 126 g of $HN{O}_3$= $6\times 6.022\times {10}^{23}$ = $36.132\times {10}^{23}$ atoms.