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
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Molar Mass |
Molecular Mass |
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It is the mass of substance in one mole. |
It is the mass of a single molecule. |
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Its unit is gram/mol. |
Its unit is an atomic mass unit (amu). |
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For example: The molar mass of water is 18 grams. |
For example The molecular mass of water is 18 amu. |
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It represents the mole mass. |
It represents the molecule 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.