Question

3. Discuss the difference between molarity and molality, state the units of each, state the symbol for each, and give an example of how each can be used when you are determining the concentration of a solution.

Answer 1

Molality(m) or molal concentration is a measure of concentration and it refers to amount of substance in a specified amount of mass of the solvent. Used unit for molality is mol/kg which is also sometimes denoted as 1 molal. It is equal to the moles of solute (the substance being dissolved) divided by the kilograms of solvent (the substance used to dissolve).

Molarity(M) or molar concentration is also a measure of concentration and represents the amount of substance per unit volume of solution(number of moles per litre of solution. Used unit for molarity is mol/L or M. A solution with a concentration of 1 mol/L is equivalent to 1 molar (1 M).

Molality is preferred when the temperature of the solution varies, because it does not depend on temperature, (neither number of moles of solute nor mass of solvent will be affected by changes of temperature), while molarity changes as temperature changes(volume of solution changes as temperature changes).