How much is a mole of water? A mole of water is Avogadro’s number of water molecules. Avogadro’s number is so large that it can be difficult to imagine its size. Finding the mass and volume of one mole of water is a great way to relate the units to something familiar. Here is the calculation for the the mass and volume of one mole of water.

### Quick Mole Review

The mole (symbol: mol) is an SI unit for the number of particles in a substance. One mole is exactly 6.02214076 x 10^{23} particles. For most calculations, the number is rounded to 6.022 x 10^{23}. This number is Avogadro’s number and its size was chosen so that the mass of one mole of a compound in grams is approximately equal to the average mass of a single molecule in daltons or atomic mass units (amu).

### Find the Mass of 1 Mole of Water

One mole of water is 6.022 x 10^{23} water molecules. To find the mass of one mole of water, follow these steps:

**Find the chemical formula.**The chemical formula for water is H_{2}O. So, each water molecule has two atoms of hydrogen and one atom of oxygen.**Look up the atomic masses of hydrogen and oxygen from the periodic table.**The atomic mass of hydrogen is 1.0079 and the atomic mass of oxygen is 15.9994.**Add the atomic masses of the elements to find the mass of one mole.**The atomic mass is the number of grams per mole of a substance. Add up the atomic masses of all the atoms in a formula to find the mass of one mole of the compound.

Mass of 1 mole of water = mass of hydrogen + mass of hydrogen + mass of water

Mass of 1 mole of water = 1.0079 g + 1.0079 g + 15.9995 g

Mass of 1 mole of water = 18.0152 g

**The mass of one mole of water is about 18 grams. **How much water is this? Unless you are familiar with small masses, this number probably doesn’t mean much to you. It’s easier to understand the amount of water if you convert the mass to volume.

### Find the Volume of 1 Mole of Water

If you know mass, you can find volume if you know density:

Density = mass / volume

Rearranging the equation:

Volume = mass / density

The density of water varies depending on temperature and pressure, but it’s very nearly 1 gram per milliliter. Plugging the mass and density into the equation gives the volume of one mole of water:

Volume = mass / density

Volume of 1 mole of water = (18 g) / (1 g/ml)

Volume of 1 mole of water = 18 ml

**One mole of water is about 18 milliliters.** This is the volume of a few drops of water, 3.65 teaspoons, 1.2 tablespoons, or 0.018 liters. It’s not a large volume, yet it contains 6.022 x 10^{23} water molecules!

You can use the same steps to find the mass and volume of any other substance. But, the mass in grams and volume in milliliters are only the same for water and other substances with a density of 1 g/ml.

### References

- de Bièvre, Paul; Peiser, H. Steffen (1992). “‘Atomic Weight’ — The Name, Its History, Definition, and Units”.
*Pure and Applied Chemistry*.**64**(10): 1535–43. doi:10.1351/pac199264101535 - Schmidt-Rohr, K. (2020). “Analysis of Two Definitions of the Mole That Are in Simultaneous Use, and Their Surprising Consequences”.
*J. Chem. Educ.***97**: 597–602. doi:10.1021/acs.jchemed.9b00467