Question

How many molecules are there in $2.570\,moles$ of ${H_2}$ ?

Answer 1

In these types of questions where we have to convert some amount of moles into atoms keep in mind these three formulas as your main steps for finding answers any of these may be as direct relation or can be found out by those. First is molar mass, it is mass in one mole, second is the Avogadro number $6.022 \times {10^{23}}\,atoms$ and third is to convert atoms into mass and molar mass.

Complete solution:
Hydrogen is the element found in the top most position in periodic table having atomic number as $1$ and mass number also $1$ so by considering the main formula by which we can convert moles into atoms or molecules is a relation of Avogadro number. Now what Avogadro number is? It gives us the specific amount of a numeric value which is present in one mole. We know from our junior classes that $1\,mole = \,6.022 \times {10^{23}}\,atoms$ .
Multiply this amount into that number which we have to change in molecules. According to molar mass of hydrogen which is $1g\,mo{l^{ - 1}}$ , it means in $1\,mole$ there is $1g\,$ of hydrogen having $6.022 \times {10^{23}}\,atoms$ or we can say $6.022 \times {10^{23}}\,molecules$. Now as we know the relation between moles and molecules, read the question again and let’s start doing the remaining calculation.
$2.570\,mole = \,2.570 \times 6.022 \times {10^{23}}\,atoms$ = $15.5 \times {10^{23}}$ molecules.

Note: This is a standard conversion as we use for one dozen, as if we want one dozen any material it will contain $12\,items$ and if we want two dozen then $12 \times 2\,\,items$ . Similarly, there are $6.022 \times {10^{23}}\,atoms\,or\,molecules$ in one mole. So if we want to calculate it for $x\,mole$ we have to just multiply $x\,mole \times 6.022 \times {10^{23}}\,atoms\,or\,molecules$