Molar Mass Of H20 (Water) Calculated And Explained

In this article, I will explain how to calculate the molar mass of water (H2O). Before you can calculate the molar mass of any substance, there are steps you need to follow.

Firstly, molar mass can be defined as mass per mole i.e. M.M = mass/mole. Said differently, molar mass is the sum of the mass of all the atoms found in one mole’s worth of a substance. Its units is grams per mole (g/mol).

How To Calculate Molar Mass of Substance

Molar mass is calculated by adding the atomic masses found in a given compound. The atomic masses of an element can be gotten from the periodic table i.e. it provides the mass of each individual element.


  • Use the correct molecular formula of the compound to determine the elements present.
  • Determine the total number of atoms for each element for instance H2 has 2 atoms of hydrogen
  • Use the periodic table to find the atomic mass of each element in the compound.
  • After you have determined the number of atoms, then multiply the number of atoms of an element by the atomic mass of one atom of that element. Repeat this for each unique element in the compound.
  • Add the values for the molar mass in the gram/mol unit.

Molar Mass of H20 (Water)

Water (H2O) has two elements which are oxygen and hydrogen. The number of atoms in hydrogen is two while that of oxygen is one.

The atomic mass of hydrogen is 1g/mol while that of oxygen is 16g/mol. Now, since hydrogen has two atoms in the compound, then it will be 1*2 = 2g/mol.

H2O = (1*2) + (16) = 2 + 16 = 18g/mol.

Therefore, the molar mass of H2O is 18g/mol.

Read: Expected topics in JAMB chemistry

Bolarinwa Olajire

A tutor with demonstrated history of working in the education industry. Skilled in analytical skills. Strong education professional with a M. SC focused in condensed matter.
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