Question

One gram atom of an element contains $6.02\times {10}^{23}$ atoms.
(a) Find the number of oxygen atoms in 4g of $O_2$.
(b) Which is heavier, one oxygen atom or 10 hydrogen atoms?

Answer 1

(a) Molecular weight of Oxygen $\left(O_2\right)=32gm/mol$

Again $1$ molecule $O_2$ contains $2$ atoms of oxygen atoms.

$\therefore$ Number of oxygen atoms is $4g$ of $O_2$

$=\frac{4}{32}\times 2\times 6.02\times {10}^{23}$

$=1.505\times {10}^{23}$

(b) Atomic weight of oxygen and hydrogen are $16gm/mol$ and $1gm/mole$ respectively.

$\therefore 6.02\times {10}^{23}$ atoms of Oxygen have total weight= $16gm$

$1$ atom of oxygen has weight= $\frac{16}{6.02}\times {10}^{-23}gm=2.657\times {10}^{-23}gm$

Similarly, $10$ hydrogen atoms have weight

$=10\times \frac{1}{6.02}\times {10}^{-23}gm=1.66\times {10}^{-23}gm$

$\therefore$ Oxygen atom is heavier than $10$ hydrogen atoms.