# How to Calculate the Number of Moles in a Solution

by Sky Smith, Demand Media

The mole, symbolized as mol, of a substance is the amount of physical quantity present in a molecule. It reduces the need of saying 6.02 x 10^23 (Avogadro's number) when describing atoms as the word "dozen" simplifies our request of 12 pastries. The mole is used in calculating the amount of molarity, or concentration, of a given substance and eases our understanding of the ideal gas law, titration, equilibrium and other chemistry principles.

### Items you will need

• Paper
• Writing utensil
• Calculator
Step 1

To find the number of moles in a solution, start by multiplying the molarity (M) by the volume (V in liters) of the solution. For example, if you have aluminum nitrate [AL(NO3)3] and want to determine the number of moles of nitrate (NO3) ions given that you have 3.00 L of a 0.340 M solution of aluminum nitrate, first calculate the number of mol in aluminum nitrate = M*V = (.340)(3.00) = 1.02 moles of aluminum nitrate.

Step 2

Determine the number of ions of your molecule of interest that are present in the substance. With the aluminum nitrate example, there are 3 (NO3) ions present in the compound.

Step 3

Multiply the number of ions of your molecule of interest to the total number of moles of the substance. Again, with the example, we would do 3*1.02 moles = 3.06 moles of (NO3). In other words, there are 3.06 moles of nitrate in the solution.

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#### References

• Chemistry; K.W. Whitten, R.E. Davis, L. Peck and G.G. Stanley, Brooks Cole, Feb. 17, 2009