# How to Calculate Molar Mass

If you are flummoxed by molar mass calculations and face conceptual problems concerning it, this post will help you out.

Omkar Phatak

Last Updated: Dec 24, 2018

Definition

Under the SI system of units, a mole is defined as the amount of a substance (a chemical element or compound), that contains as many elementary entities (molecules, atoms, or ions), as there are atoms in 12 gm of carbon-12. A mole contains exactly 6.023 x 10

^{23}(Avogadro's number) elementary entities (atoms, molecules, or ions) of that substance.^{23}molecules and atoms. So, molar mass of a substance is the mass of one mole of that substance. Keep a periodic table with atomic mass in front of you, along with a calculator. Also, while calculating, you need to know the molecular formula of the concerned compound.

Calculation For Elements

Molar mass of an element is the atomic weight of the element, expressed in grams/mol. See which element's mass is to be calculated and note its standard atomic weight. Multiply it by 1 g/mol, which is the standard constant. The product of the standard atomic weight of the element with 1 g/mol, will give you the molar mass.

Calculation For Compounds

The molar mass of a compound is a sum of the molar masses of atoms, that make the compound. Here is the calculation procedure. Get the molecular formula of the compound. Note down the different atomic elements that are contained in the molecular formula, along with the number of atoms of each element.

_{2}O. Hydrogen has two atoms while oxygen has only one. Therefore,

Molar mass of Water (H

_{2}O) = (2 x 1.00794 + 1 x 15.9994 ) x 1 gm/mol = 18.015 gm/mol

Calculating this parameter is purely a plug-in problem, once you understand the concept. Just put in the numbers and get the answer.