Tap to Read ➤

Molar Mass of NaOH

Omkar Phatak May 13, 2019
This write-up computes the molar mass of sodium hydroxide for you, besides explaining all the basic analytical chemistry concepts involved.
When taking your first chemistry class in high school, or your undergraduate years, you will come across many concepts which need to be understood, to successfully carry out lab experiments. One such concept is the molar mass of any compound.


Molar mass or gram mole of any compound is its exact molecular weight (computed from summing up of atomic weights together) expressed in grams. It is generally expressed in grams or gram/mol. One mole is unit molar mass of that substance, expressed in grams. For example, one gram mole of water is 18 gm or 18 gm/mol.

Calculation Technique

You may know sodium hydroxide (NaOH) as 'caustic soda' or 'lye', as it finds many applications in the manufacturing of soaps, detergents, and even textiles. Its wide applicability is owed to it being a strong base.
Besides being used in chemical industries, NaOH finds use as a cleansing agent. When used in chemical industries and chemistry labs, as part of chemical reactions, sodium hydroxide needs to be used in the form of standardized solutions. To create such solutions of specific molarity, molality, or normality, you need to know their molar mass.
To calculate one gram mole of sodium hydroxide, you need to first calculate its molecular weight. To be able to do that, you will have to know the atomic weights of the constituent chemical elements, which are sodium, oxygen, and hydrogen.
Refer to a periodic table with atomic weights and compute the molecular weights of the compound. Once you have the molecular weight of NaOH, you are essentially done, as when it's expressed in grams, you have the molar mass.


Firstly, we need to know the atomic weights of hydrogen and oxygen. While sodium's standard atomic weight is 22.98976928, hydrogen's standard atomic weight is 1, and oxygen has a standard atomic weight of 15.9994.
Molecular Weight of NaOH = Atomic Weight of Sodium + Atomic Weight of Oxygen + Atomic Weight of Hydrogen = 22.98976928 + 1 + 15.9994 = 39.9892
So, the molar mass is 39.9892 gm/mol. The value has been rounded up only after the fourth decimal, as measurements in chemistry need to be as accurate as possible.