Question

Exactly $1mol$ of $Pb{\left( {Cl{O_2}} \right)_2}$ contains how many moles of $Pb$, $Cl$, and $O$?

Answer 1

We need to understand the mole concept in order to calculate the number of moles of the constituent atoms in a given compound. Mole concept is a convenient concept for expressing the amount of a given substance. In chemistry, a mole is defined as the amount of a substance which contains Avogadro’s number of particles. Using this concept we can calculate the number of moles of $Pb$, $Cl$, and $O$ in one mole of $Pb{\left( {Cl{O_2}} \right)_2}$.

Complete step by step answer:
The number of moles of a substance we can calculated by the following formula given below:
$n = \dfrac{N}{{{N_A}}}$
Where $n$ is the number of moles of the substance $N$ is the total number of entities of the particular element in the sample, and ${N_A}$ is the Avogadro’s constant whose value is $6.022 \times {10^{23}}$.
Let us take the example of one mole of carbon-12 whose mass is 12 grams and contains $6.022 \times {10^{23}}$ number of atoms.
From the given chemical formula $Pb{\left( {Cl{O_2}} \right)_2}$, we can see from the subscripts that there is one mole $Pb$, two moles $Cl$ and four moles $O$. Since there is one mole of $Pb{\left( {Cl{O_2}} \right)_2}$ , its ratio with each constituent atom will calculate the total number of moles in one mole of its compound. Hence here ${N_A} = 1mole$ $Pb{\left( {Cl{O_2}} \right)_2}$ and ${N_{Pb}} = 1,{N_{Cl}} = 2,{N_O} = 4$.
Therefore, ${n_{Pb}} = \dfrac{{{N_{Pb}}}}{{{N_A}}} = \dfrac{1}{1} = 1mol$
${n_{Cl}} = \dfrac{{{N_{Cl}}}}{{{N_A}}} = \dfrac{2}{1} = 2mol$
${n_O} = \dfrac{{{N_O}}}{{{N_A}}} = \dfrac{4}{1} = 4mol$
Hence 1 mol of $Pb{\left( {Cl{O_2}} \right)_2}$ contains 1 mol of $Pb$, 2 mol of $Cl$ and 4 mol of $O$.

Note:
It must be noted that since there is only one mole of a compound, its constituent atoms will contain a number of moles which is equal to the number of atoms. The number of moles of a molecule may not always be equal to the number of moles of its constituent elements. For example, a mole of water contains NA number of H2O molecules. However, each water molecule contains 2 hydrogen atoms and one oxygen atom. Therefore, one mole of H2O contains 2 moles of hydrogen and one mole of oxygen.