Question

How many moles of aluminium, sulphur, and oxygen atoms are there in ${\text{7}}{\text{.00}}$ moles of aluminium sulphate, ${\text{A}}{{\text{l}}_2}{{\text{(S}}{{\text{O}}_4}{\text{)}}_3}$?

Answer 1

o determine the answer we should know that moles of atoms combines in a fix ratio to give a mole of molecule. We have the molecular formula of aluminium sulphate. From the molecular formula we can determine the moles of each constituting atom present in one mole of the molecule. So, as we have mole of an atom in one mole of molecule we can determine the moles of atoms in x mole of molecule.

Complete step-by-step answer: The given formula of aluminium sulphate is ${\text{A}}{{\text{l}}_2}{{\text{(S}}{{\text{O}}_4}{\text{)}}_3}$. From this formula we can say one mole of aluminium sulphate is made up of two moles of aluminium atoms, three moles of sulphur atoms and twelve moles of oxygen atoms.So, if one moles of aluminium sulphate contains two moles of aluminium atoms then seven moles of aluminium sulphate will contain,
$1$ mol ${\text{A}}{{\text{l}}_2}{{\text{(S}}{{\text{O}}_4}{\text{)}}_3}$ = $2$ mol Al
$7$ mol ${\text{A}}{{\text{l}}_2}{{\text{(S}}{{\text{O}}_4}{\text{)}}_3}$ = $14$ mol Al
So, seven moles of aluminium sulphate will contain fourteen moles of aluminium atoms.
Similarly, if one moles of aluminium sulphate contains three moles of sulphur atoms then seven moles of aluminium sulphate will contain,
$1$ mol ${\text{A}}{{\text{l}}_2}{{\text{(S}}{{\text{O}}_4}{\text{)}}_3}$ = $3$ mol S
$7$ mol ${\text{A}}{{\text{l}}_2}{{\text{(S}}{{\text{O}}_4}{\text{)}}_3}$ = $21$ mol S
So, seven moles of aluminium sulphate will contain twenty-one moles of sulphur atoms.
Similarly, if one moles of aluminium sulphate contains twelve moles of oxygen atoms then seven moles of aluminium sulphate will contain,
$1$ mol ${\text{A}}{{\text{l}}_2}{{\text{(S}}{{\text{O}}_4}{\text{)}}_3}$ = $12$ mol O
$7$ mol ${\text{A}}{{\text{l}}_2}{{\text{(S}}{{\text{O}}_4}{\text{)}}_3}$ = $84$ mol O
So, seven moles of aluminium sulphate will contain eighty-four moles of oxygen atoms.

Therefore, $14$moles of aluminium, $21$moles of sulphur, and $84$moles of oxygen atoms are there in ${\text{7}}{\text{.00}}$ moles of aluminium sulphate, ${\text{A}}{{\text{l}}_2}{{\text{(S}}{{\text{O}}_4}{\text{)}}_3}$.

Note: The subscript present after an atom shows the number of that atom. The subscript present after a bracket presents the number of all the atoms present inside the bracket. In ${\text{A}}{{\text{l}}_2}{{\text{(S}}{{\text{O}}_4}{\text{)}}_3}$, $3$ outside the bracket shows the three atoms of sulphur and three atoms of oxygen. The oxygen has subscript$4$, means four oxygen atoms, so the total number of oxygen atoms are ($3 \times 4$), twelve.