What is the difference between Molarity and Molality ?

Molarity tells us the number of moles of solute in exactly one liter of a solution. (Note that molarity is spelled with an "r" and is represented by a capital M.)

 

Molarity =   moles of solute

                Volume of solution in litres

 

Molality, m, tells us the number of moles of solute dissolved in exactly one kilogram of solvent. (Note that molality is spelled with two "l"'s and represented by a lower case m.)

 

Molality = moles of solute

              Mass of solvent in kilograms