Question

What is the molar mass of $S{O}_3$ ?

Answer 1

Hint: Molar mass of a compound is the sum of the atomic weights of all the elements that constitute in the compound. The no. of atoms of each element in the compound is also considered and the total mass of the individual elements in the compound, are summed up to know the molar mass.

Complete answer:
The compound given to us is $S{O}_3$. One molecule of $S{O}_3$ consists of one atom of Sulphur and three atoms of Oxygen. To calculate the molar mass we must know the atomic mass of sulphur and oxygen.
Atomic weight of Sulphur $=32$
Atomic weight of Oxygen $=16$
No. of atoms of Oxygen present in $S{O}_3=3$
Molar mass of $S{O}_3$ = Atomic weight of sulphur $+3\times$ Atomic weight of Oxygen.
$S{O}_3=32+3(16)$
$S{O}_3=32+48=80g/mol$
Therefore, the molar mass of $S{O}_3$ is $80g/mol$.

Additional Information:
Sulphur trioxide is also known as sulfuric anhydride. It is colourless and forms fumes when exposed to air. It is a strong oxidising agent and is highly reactive. Thermodynamically, it is an unstable compound.

Note:
From above we have seen that the unit of molar mass is g/mol (gram per mole). From this we can say that the molar mass of any compound can be given as the mass of the compound (in grams) divided by the amount of that substance in moles. Alternatively, molar mass is also the mass or weight (in grams) of one mole of the compound. Remember that molar mass and molecular weight are two different concepts. Molecular weight is the mass of one molecule of that compound, whereas molar mass is the mass of one mole of that particular compound.