Isolation of Elements


Concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration .

How To Calculate Units of Concentration

Once you have identified the solute and solvent in a solution, you are ready to determine its concentration. Concentration may be expressed several different ways, using percent composition by mass, volume percent,mole fraction, molarity, molality, or normality.

Mass concentration

The mass concentration pi is defined as the mass of a constituent mi divided by the volume of the mixture V

Pi =mi / V

The SI unit is kg/m3 (equal to g/L).

Molar concentration

This is the number of moles of a compound divided by the total number of moles of all chemical species in the solution. Keep in mind, the sum of all mole fractions in a solution always equals 1.


What are the mole fractions of the components of the solution formed when 92 g glycerol is mixed with 90 g water? (molecular weight water = 18; molecular weight of glycerol = 92)

Molarity (M)

Molarity is probably the most commonly used unit of concentration. It is the number of moles of solute per liter of solution (not necessarily the same as the volume of solvent!).


Normality is defined as the molar concentration Ci divided by an equivalence factor feq. Since the definition of the equivalence factor depends on context IUPAC and NIST discourage the use of normality.


The molality (m) of a solution is used to represent the amount of moles of solute per kilogram of the solvent.

m=Moles of Solute / Kilograms of Solvent