Question

The chemical formula for Magnesium Sulphate is $\text{Mgs}{{\text{o}}_{4}}$. What is the relative formula mass of the compound?

Answer 1

Hint: Relative formula mass is defined as the ratio of average mass of atoms of a chemical element to the atomic mass constant. This atomic constant is the one-twelfth of the mass of a carbon-12 atom. Relative formula mass is a dimensionless quantity.

Complete step by step answer:
The relative mass of denoted by ${{\text{M}}_{r}}$means mass of molecule and the ${{\text{M}}_{r}}$ is obtained by
${{\text{A}}_{r}}$ where ${{\text{A}}_{r}}$ is atomic mass of the atom from a molecule.
For the molecule of $\text{Mgs}{{\text{o}}_{4}}$ (Magnesium Sulphate)
We have
$\text{Mg}$ (magnesium) Atomic number $=12$
Atomic mass $\text{(}{{\text{A}}_{\text{r}}}\text{)}$ is just double (approximately) to the atomic number so the ${{\text{A}}_{\text{r}}}$for magnesium is $24.31$.
Similarly you sulphur to the Atomic number of Sulphur atoms is $16$. Hence the atomic mass ${{\text{A}}_{\text{r}}}$ will be $32.001$. And for the oxygen atom, it has atomic number $8$ and for $4$ oxygen atom the Atomic mass $\text{(}{{\text{A}}_{\text{r}}}\text{)}$ with $4\times 16=64.$The unit of mass will grams /moles in the molecule we have the all atomic mass of follows:
For magnesium $=24.31$ grams/mole
For Sulphur $=32.01$ grams/mole
For oxygen ($4$ oxygen atoms) $=64$ grams/mole
Conclusions: The total mass $=$ mass of magnesium $+$ mass of sulphur $+$ mass of oxygen
The total mass $=(24.30+32.001+64)$ grams/mole
$=120.38$ grams/mole
Above we have the molecular mass for the molecule of magnesium Sulphate
More Details: By the addition of relative mass of all the atoms which present in the molecules
\[{{\text{M}}_{r}}={{\text{A}}_{{{\text{r}}_{\text{1}}}}}+{{\text{A}}_{{{\text{r}}_{\text{2}}}}}+{{\text{A}}_{{{\text{r}}_{\text{3}}}}}+{{\text{A}}_{{{\text{r}}_{\text{4}}}}}+...\]
This is a very easy calculation to get the mass of a molecule if you don‘t have the exact Atomic mass then you can also apply which is just double to the atomic number most of the atoms have just double atomic numbers.

Note: For getting the individual atomic mass we should have the atomic number of including atoms, which are involved in molecule formation. With the help of relative mass of any molecule. We can calculate so many values of the molecule by which we have the many properties and characteristics of molecules.