Meaning of Molar Mass

What is Molar Mass:

The molar mass (M) is the amount of mass a substance contains in one mole. One mole is defined as 6.022 x10 23 particles.

On the periodic table, the molar mass of the elements, also called the atomic mass or atomic weight, can be found at the bottom of the element. Hydrogen, for example, has a molecular mass of 1.008 gr/mol and nitrogen 14.01 gr/mol.

To calculate the molecular mass of a compound, also called mass or molecular weight, such as ammonia (NH3) the molar mass of the elements of the compound must be added multiplied by the times they appear, for example:

molar mass of NH3 =

1 molecule of Nitrogen times its atomic mass of 14.01 plus 3 molecules of Hydrogen times its atomic mass of 1.008 = (1 * 14.01) + (3 * 1.008) = 14.01 + 3.024 = 43.038 u = 17.03 molecular mass = 17.03 g/mol of molar mass in ammonia.

When the molar mass of a compound is known, the number of moles per gram is known, remembering that each mole is 6.022 x 1023 particles.

Therefore, knowing the molar mass, the number of moles in a container can be calculated using the formula:

mole = mass / molar mass.

For example, in 100 grams of ammonia (NH3) to find the number of moles we must divide 100 / 17.03 g/mol which gives an approximate result of 5.8 moles in 100 grams of ammonia.

In chemistry, the molar mass is important to determine the weight of the amount of mass that is required of a substance, since our balances are calibrated by weight and not by mass. That is why molar mass is generally expressed in kilograms per mole (kg/mol) or grams per mole (g/mol).

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See also:

  • Dough
  • Kilogram
  • stoichiometry
  • chemical concentration