What is the difference between molarity and molality?

Molarity and molality are two ways to express the concentration of a solution. Molarity is calculated by dividing the moles of the solute by the volume of the solution in liters. Molarity is used to calculate the pH and pOH of acids and bases. Molality is calculated by dividing the moles of the solute by the mass of the solvent in kilograms. Molality is used to express concentrations of solutions that are at or near the freezing point and boiling point of water. This is because the volume of water varies with temperature especially at the melting and freezing points, but mass is not affect by temperature. Molarity's symbol is M and molality's symbol is m.