Question

Compute the mass of one molecule and the molecular mass of ${C_6}{H_6}$ (Benzene).
(Atomic mass of C=12 u , H=1 u).

Answer 1

‘u’ unit stands for atomic mass unit. We can also take ‘u’ as g/mol. One mole of any species contains $6.022 \times {10^{23}}$ number of species. Molecular mass is the mass of 1 mole of any compound.

Complete Step-by-Step Solution:
We will calculate the molecular mass of benzene first and then we will find the mass of one molecule of benzene. We know that the molecular mass of benzene is the mass of one mole of benzene molecules. We are given the atomic masses of carbon and hydrogen atoms. ‘u’ unit stands for atomic mass unit. We can also take ‘u’ as g/mol. So, we can say that the weight of one mole of carbon atoms and hydrogen atoms is 12 g and 1 g respectively. Now, we will calculate the molecular mass of ${C_6}{H_6}$.
Molecular mass of ${C_6}{H_6}$ = 6(Atomic mass of C) + 6(Atomic mass of H)
Molecular mass of ${C_6}{H_6}$ = 6(12) + 6(1)
Molecular mass of ${C_6}{H_6}$ = 72 + 6 = 78 $gmo{l^{ - 1}}$
Now, we will calculate the mass of one molecule of benzene using its molecular weight,
- We already know that one mole of any species contains $6.022 \times {10^{23}}$ number of species.
-So, we can say that 1 mole of benzene molecules will contain $6.022 \times {10^{23}}$ molecules.
-Now, if weight of $6.022 \times {10^{23}}$ molecules of ${C_6}{H_6}$ is 78 g
Then weight of 1 molecule of ${C_6}{H_6}$ = $\dfrac{{1 \times 78}}{{6.022 \times {{10}^{23}}}} = 1.2952 \times {10^{ - 22}}$ g

Thus, we can conclude that the molecular weight of ${C_6}{H_6}$ is 78 $gmo{l^{ - 1}}$ and the weight of 1 molecule of ${C_6}{H_6}$ is $1.2952 \times {10^{ - 22}}$g.

Note: Atomic mass unit is the unit of mass to express the mass of atoms. The symbol of the atomic mass unit is Da or u. It is also called Dalton. 1 atomic mass unit is defined as $\dfrac{1}{{12}}$ of the mass of the carbon-12 isotope.