Question

What is the molar mass iron (III) oxide $F{{e}_{2}}{{O}_{3}}$ ?

Answer 1

Hint: The number in the subscript tells us the number of atoms of the element that are involved in that compound. Iron exists in two types of oxides, here the oxidation state of iron is +3.

Complete answer: We have been given a compound iron (III) oxide $F{{e}_{2}}{{O}_{3}}$. We have to find its molecular weight or molar mass.
The molar mass of any compound is the sum of the atomic masses of all the atoms of the constituent elements of that compound multiplied by the number of atoms of the constituent elements.
Iron (III) oxide $F{{e}_{2}}{{O}_{3}}$, as we can see, contains 2 iron atoms, $F{{e}_{2}}$ , and 3 oxygen atoms,${{O}_{3}}$, so the atomic mass of iron, 55.85 g/mol, and of oxygen, 16 g/mol, is to be multiplied by 2 and 3 respectively will give us their molar masses. This can be calculated as,
Molar mass of $F{{e}_{2}}$ = 2 $\times $ 55.85 g/mol = 111.7 g/mol
Molar mass of ${{O}_{3}}$ = 3 $\times $ 16 g/mol = 48 g/mol
Now we got the molar masses of the elements, to find the molar mass of iron (III) oxide, we will add the molar masses of iron and oxygen as,
Molar mass of $F{{e}_{2}}{{O}_{3}}$= Molar mass of $F{{e}_{2}}$+ Molar mass of ${{O}_{3}}$
Molar mass of $F{{e}_{2}}{{O}_{3}}$= 111.7 g/mol + 48 g/mol
Molar mass of $F{{e}_{2}}{{O}_{3}}$= 159.70 g/mol
Hence, the molar mass of Iron (III) oxide $F{{e}_{2}}{{O}_{3}}$is calculated as 159.70 gram per mole.

Note: The atomic mass of any element is written in gram per mole, because it is the mass of that element in 1 mole of the atoms of that element or we can say that in $6.022\times {{10}^{23}}$ particles of that element.