Question

What is the number of atoms of hydrogen present in one dozen molecules of hydrogen gas? Convert the given number of hydrogen in terms of moles.

Answer 1

A molecule of hydrogen is formed when two atoms of hydrogen combine with each other. Hence, one molecule of hydrogen contains two atoms of hydrogen. Therefore,
One molecule of hydrogen = 2 atoms of hydrogen
12 molecules (one dozen) of hydrogen molecules $=12\times 12=24$ atoms of hydrogen
So, there are 24 atoms of hydrogen in one dozen of hydrogen molecules. Now, one mole of hydrogen contains $6.022\times {10}^{23}$ of hydrogen atoms, that is $6.022\times {10}^{23}$ atoms of hydrogen = 1 mole of hydrogen
So, 24 atoms of hydrogen $=\frac{24}{(6.022\times {10}^{23})}$ moles of hydrogen atom
$=3.985\times {10}^{-23}$ moles of hydrogen atom
Now the molar mass of hydrogen is 1 g. This means that there are $6.022\times {10}^{23}$ atoms of hydrogen in 1 g of hydrogen. As one mole of any substance contains $6.022\times {10}^{23}$ atoms, therefore
1g = 1 mole of H atom
Now as the molar mass of $H_2$ molecule is 2g, therefore
2 g of $H_2$ molecule = 1 mole of $H_2$ molecule
1 g of $H_2$ molecule $=\left(\frac{1}{2}\right)$ mole of $H_2$ molecule
24 g of $H_2$ molecule $=\left(\frac{24}{2}\right)$ mole of $H_2$ molecule
= 12 moles of $H_2$ molecule.