Difference between Molarity and Molality
Key Difference: Molarity, also known as molar concentration, measures the number of moles of a
substance present in per liter of solution. Molarity is denoted with a capital M. Molality measures the number of
moles of a substance present in per kilogram of solvent. Molality is denoted with a lower case m.
The term ‘molarity’ and ‘molality’ are two terms that are commonly heard in chemistry. These
are two units that are used for measuring the concentration of solutions. The concept of molarity
and molality are very confusing for people that are just learning these terms as they seem similar
and are both used as measurements. However, these two terms differ in how they measure a
particular concentration.
Both of the concepts base their calculations on how many moles are present in the current
solution. A solution can be defined as a homogeneous mixture, which means two or more
components have been mixed to the point that it cannot be distinguished by the naked eye. These
two concepts require understanding moles as it determines the number of moles present in the
solution. The theory of moles was discovered by Italian scientist, Amedeo Avogardo.
In 1811, Avogardo proposed that the volume of gas, at a given temperature and pressure, is
proportional to the number of atoms or molecules regardless of its nature. This concept is known
as the Avogardo constant. It is defined as the number of constituent particles (usually atoms or
molecules) in one mole of a given substance. In laymen terms, one mole of a substance would
represent the number of atoms and molecules present in the element. For example: Oxygen has
an atomic weight of 16, this would represent the mass of per mole of oxygen. So, one mole of
oxygen would have a mass of 16 grams. According to Avogardo, one mole of oxygen would
have the same number of atoms as one mole of hydrogen. However, they can differ in weight.
