Question

Calculate the number of atoms in $16g$ of oxygen molecules.

Answer 1

Hint: Avogadro’s law should be known for proving the answer of this question. The Avogadro’s number is $6.023\times {10}^{23}$. The atomic mass of oxygen is $16u$ and it is calculated by adding the number of protons and neutrons present in the nucleus of the cell.
Formulas used: Number of moles, $n={\displaystyle \frac{W}{M}}$
Where $W$ is the given mass and $M$ is the molar mass.

Complete step by step answer:
Firstly, we know that the molar mass of oxygen molecule is $32g$.
Therefore, $M=32g$
Now we know that the given mass is $16g$,
That is, $W=16g$
Now we find out the number of moles in an oxygen molecule,
Number of moles, $n={\displaystyle \frac{W}{M}}$ Where $W$ is the given mass and $M$ is the molar mass.
$\Rightarrow n={\displaystyle \frac{16}{32}}$
$\Rightarrow n=0.5moles$
Therefore, there are $0.5moles$ in a single oxygen molecule.
Now we look to find out the number of molecules in the $0.5moles$ of oxygen molecule,
Number of molecules is equal to the number of moles multiplied by the Avogadro’s number,
That is $\Rightarrow 0.5\times 6.023\times {10}^{23}$
$\Rightarrow 3.011\times {10}^{23}$ number of molecules are present in $0.5moles$ of oxygen molecules.
There are two oxygen atoms in a single oxygen molecule and this number of atoms is multiplied with the number of molecules.
So, the number of atoms, $n_a=2\times 3.011\times {10}^{23}$
$\Rightarrow n_a=6.023\times {10}^{23}$, hence the number of atoms present in $16g$ of oxygen molecule is $6.023\times {10}^{23}$.

Additional information: A diatomic molecule consisting of two oxygen atoms held together by a covalent bond is molecular oxygen. Molecular oxygen, as it is used by many species for respiration, is important for life. It's also important for the combustion of fossil fuels. At standard temperature and pressure, oxygen is a colorless, odorless, and tasteless gas with the molecular formula $O_2$ referred to as dioxygen.

Note:Molar mass of a compound is the mass of the compound which will have the number of molecules in that mass to be equal to the Avogadro number. As the measurable mass of a compound is only its molar mass, the Avogadro number helps us to find the masses of atoms and other small particles. Note that the SI unit of the Avogadro number is the inverse of mole, i.e., $mol{e}^{-1}$.