Question

What is the mass of one molecule of oxygen?

Answer 1

Mole:

• One mole of a substance contains exactly $6.022\times {10}^{23}$ elementary entities. This number is called Avogadro's constant.
• The elementary entities may be an atom, a molecule, an ion, an electron, or any other particle.

Step 1: Molar mass of oxygen$\left({\mathrm{O}}_2\right)$:

• The molar mass of oxygen $=16\times 2=32{\mathrm{gmol}}^{-1}$.
• It means that 1 mole of oxygen has mass $=32\mathrm{g}$

Step 2: Mass of one molecule of oxygen:

• 1 mole of oxygen$=6.022\times {10}^{23}$molecules of oxygen
• The mass of $6.022\times {10}^{23}$ molecules of oxygen $=32\mathrm{g}$
• So, the mass of $1$ molecule of oxygen $=\frac{1}{6.022\times {10}^{23}}\times 32\mathrm{g}=5.314\times {10}^{-23}\mathrm{g}$

Therefore, the mass of one molecule of oxygen is $\mathbf{5}\mathbf{.}\mathbf{314}\mathbf{}\mathbf{\times }\mathbf{}{\mathbf{10}}^{\mathbf{-}\mathbf{23}}\mathbf{}\mathbf{g}$.