Molar Mass: Definition, Calculation, and Examples

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What is Molar Mass?

 Molecules and atoms are very minute, both in size and mass.

 The molar mass is defined as the weight of one sample mole.

 Relative molar mass is referred to as the smallest mass unit of a compound of one-twelfth of the mass of one carbon – 12 atoms.

 The amount of entities present in a particular substance such as atoms, molecules, ions, is defined as a mole.

 A mole of any substance is written as 6.022×1023 molecules.

 The molar mass of a substance which is also known as the molecular weight is defined as the sum of the total mass in grams of all the atoms that make up a mole of a particular molecule.

 The unit of this quantity is expressed in grams per mole.

How to Find the Molar Mass for Compounds?

Compounds are defined as substances that are made up of more than one element. For instance, some general compounds include salt, glucose and acetic acid (or vinegar), etc.

For instance; the compound sodium chloride comprises of two elements which are, sodium and chlorine.

Molar Mass Formula

The molar mass of a compound is defined as the mass of an assumed substance divided by the quantity of substance present in the sample.

Molar Mass = Mass of given substance/amount of substance

The molar mass is an intensive property of the matter and it doesn’t depend upon the dimensions of the sample.

The SI unit of molar mass is kg/mol. Though, for ancient reasons molar masses are almost always expressed in g/mol.

Atomic Mass

The meaning of atomic mass, the mole, and molar mass are all directly or indirectly connected to carbon-12.

This results in two important facts mentioned below;

• The atomic mass of one atom of carbon-12 is precisely 12 atomic mass units or amu.

• The mass of one mole of carbon-12 atoms is also precisely 12 grams and its molar mass is accurately 12 grams per mole.

NOTE: The atomic mass and the molar mass of carbon-12 are statistically equal. They only differ only in SI units; atomic mass is commonly measured in atomic mass units, and molar mass is generally measured in grams per mole.

Mole Definition

In chemistry, the mole is a fundamental (SI) unit used to measure the amount of substance. This quantity is sometimes referred to as the chemical amount. A substance is something that has mass and occupies space.

The molar mass / molecular weight is truly the sum of the total mass in grams of the atoms present to make up a molecule per mole. The unit of molar mass is grams/mole.

How to Determine Molar Mass of a Compound?

To find the molar mass of NaOH.

In a given compound of NaOH, the molar mass of Na is equal to 23 g/mol, the molar mass of O is equal to 16 g/mol, and the molar mass of H is 1 g/mol.

Na+O+H = NaOH

23 g/mol+16 g/mol+1 g/mol= 40 g/mol

The molar mass of the given compound of NaOH is equal to 40 g/mol.

Molar Mass Calculation

The molar mass of a compound is frequently calculated by adding the quantity of atomic masses (in g/mol) of the given constituent atoms.

The property of the molar mass of a given component is just the mass in g/mol.

Though, molar mass also can be calculated by multiplying the mass expressed in amu by the molar mass constant.

For instance; Find the molar mass of hydrogen (H2), sulfur (S8) by using the Molar Mass Formula.

The molar mass of molecules of those elements is always equal to the molar mass of the given atoms multiplied by the number of atoms present in each molecule.


Molar Mass of (H2) is equal to 2 × 1.00797(7) × 1.000000 g/mol = 2.01588(14) g/mol

Molar Mass (S8) is equal to 8 × 32.065(5) × 1.000000 g/mol = 256.52(4) g/mol

Molar Mass Citations


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