Isomers are special compounds that have the same chemical formula but are put together in different ways.

This difference in structure can change their physical and chemical properties, including something called molar mass.

But here’s a key point: the molar masses of isomers can be the same because they have the same types and amounts of atoms.

How to Calculate Molar Mass

To find out the molar mass of a compound, you add up the molar masses of all the atoms based on its molecular formula.

Let’s look at two isomers: butane (C₄H₁₀) and isobutane (C₄H₁₀).

• For Butane:

  • Carbon (C): $12.01 \, \text{g/mol} \times 4 = 48.04 \, \text{g/mol}$
  • Hydrogen (H): $1.01 \, \text{g/mol} \times 10 = 10.10 \, \text{g/mol}$
  • Total Molar Mass of Butane: $48.04 + 10.10 = 58.14 \, \text{g/mol}$

• For Isobutane:

  • It also has 4 Carbon atoms and 10 Hydrogen atoms.
  • Total Molar Mass of Isobutane: $58.14 \, \text{g/mol}$

In Summary

Even though butane and isobutane are arranged differently (butane is straight while isobutane has branches), they both have the same molar mass of $58.14 \, \text{g/mol}$.

This shows that while their structures can be different, the molar mass can still be the same because the amounts of each type of atom are identical.