Question

You have \[1.45\] moles of hydrogen. How many atoms are present?

Answer 1

Hint: To answer this question we should know what is mole i.e. mole concept, Avogadro’sNumber, what type of hydrogen atom is whether monatomic or diatomic. Here hydrogen is diatomic i.e. it is a molecule with two atoms (\[{{{H}}_{{2}}}\]) and both are the same. Here both atoms being the same we can say that hydrogen is homonuclear. Similarly oxygen is also another example of a homonuclear with diatomic molecule. If a diatomic molecule has two different atoms then it is called as heteronuclear, for eg. \[{{CO}}\] .

Complete step by step answer:
We need to remember that mole is the SI unit for the amount of substance and can be denoted by mol. It can be defined as the amount of substance which contains the same number of particles (i.e. atoms or molecules) found in \[12\] grams of carbon -\[12\]. Here the number of particles represent Avogadro’s Number. It is denoted by \[{{{N}}_{{A}}}\] and its value is \[{{6}}{{.023 \times 1}}{{{0}}^{{{23}}}}\] .The number \[{{6}}{{.023 \times 1}}{{{0}}^{{{23}}}}\] indicates the number of atoms or molecules in one mole of a substance.
We know that in \[1\] mole of element there are \[{{6}}{{.023 \times 1}}{{{0}}^{{{23}}}}\] particles.
\[\therefore \] In \[1.45\] moles of hydrogen there are\[{{ 1}}{{.45}} \times {{6}}{{.023}} \times {{1}}{{{0}}^{23}}{{ = 8}}{{.7319}} \times {{1}}{{{0}}^{23}}\] particles.
Now here hydrogen is diatomic molecule,
So \[{{2 \times 8}}{{.7319 \times 1}}{{{0}}^{{{23}}}} = 1.74638 \times {10^{24}}\].
\[\therefore \] In \[1.45\] moles of hydrogen there are \[1.74638 \times {10^{24}}\] particles.

Note:
 We need to remember that the Avogadro’s Number is also known as Avogadro constant. As we know atoms or molecules are small entities which makes it difficult for chemists to work and find the result, the mole concept was introduced. It should be noted that there is a relation between mole, Avogadro’s Number and formula mass. With the help of this relation we can determine the composition of any substance. If we know the number of moles we can calculate the number of atoms and formula mass of the given substance.