[Chemistry Class Notes] on Molar Mass Formula Pdf for Exam

What is Molar Mass?

The mass contained in one mole of a substance is called molar mass. It can also be defined as the amount of substance in grams present in one mole of the substance. In one mole 6.023 × 1023 molecules are present. This number is called Avogadro’s number. Molar mass is the most important term used in physical chemistry. In this article, we will cover the molar mass, molar mass formula, molecular mass and its formula, the difference between the molar and molecular mass, and relative molar mass and its formula.

Difference Between Molar Mass and Molecular Mass

What is Relative Molecular Mass?

The relative molecular mass of a substance is the sum of the atomic masses of all the atoms in a molecule of the substance. It is measured in terms of u (unified mass).

Molar Mass Formula and Molecular Mass Formula 

Molecular Mass

Molecular mass (AB2) = atomic mass of A + 2 × atomic mass of B 

Molar Mass

Molar mass (AB2) = atomic mass (in grams) of A + 2 × atomic mass of B (in grams)

Solved Examples 

Example: Find the molecular of the water molecule.

Solution: The formula of the water molecule is H₂O.

The atomic mass of hydrogen = 1 amu

The atomic mass of oxygen = 16 amu

Molar mass of water = 2 *1 + 16 = 18 amu.

Example: What will be the relative molar mass of the hydrogen molecule.

Solution: Hydrogen molecule represented by H₂.

The relative molecular mass of hydrogen molecule = sum of the relative atomic masses of two atoms of hydrogen.

⇒ 1U + 1U = 2U.

Conclusion

Molar mass, molecular mass and relative molar mass are differ from each other in terms of the unit they express. Molar mass represents the weight of one mole molecule in g/mol, molecular mass represents the weight of one molecule in amu and relative molar mass represents the weight of a single atom in terms of ununified mass.