What is mol?

The word mol was first used by the chemist Wilhem Ostwald in 1896. In Latin, this word means soft, which means "mound", "quantity".

From this word also originated moleculewhich means small amount. Some goods are sold in quantities already defined, such as the dozen (12), the ream (500), etc. The mol also determines quantity.

It can also determine mass and volume. See the following scheme:

One mole of anything has 6.02.1023 units. It is used in chemistry to refer to microscopic matter, as this number is very large.

It can be used to quantify atoms, molecules, ions, number of electrons, etc. The number 6.02.1023 is the constant of Avogadro. Examples:

1 mol of H atoms has 6.02.1023 atoms
2 mol of H atoms is 2 x 6.02.1023 atoms = 12.04.1023 H atoms

The mol indicates mass. One mole of an element is equal to its molecular mass in grams (g). Examples:

1 mol of water has 18g
2 mol of water has 2 x 18 = 36g

The mol indicates volume. In fact, it indicates the volume occupied by a gas in CNTP (normal temperature and pressure conditions). For gases that are in these conditions, the value of one mol is 22.4L (liters).

T = 0 ° C = 273K
P = 1atm = 760mmHg


1 mol of CO2 What volume does CNTP occupy? 22.4L
2 mol CO2 What volume does CNTP occupy? 2 x 22.4L = 44.8L

For gases that are not in these conditions, use the Ideal Gas formula or Clapeyron equation:

P.V = n.R.T

P = gas pressure (atm)
V = gas volume (L)
n = number of moles of gas (mol)
R = Clapeyron constant = 0.082 atm.L / mol.K
T = gas temperature (K)

Spelling and plural

The unit name "mol" must always be spelled in lower case. As for the plural, be careful because the unit name accepts the plural "mols" as in the example:

"How many moles are there in this substance?"

However, mol as a symbol of unity does not accept plural. Example:

3.0 mol (not 3.0 mol)

That is, it works similarly to other units of the international system, such as the meter: 5 m (not 5 ms).