Percent by Mass . The mass of the solution is equal to the mass of the solute plus the mass of the solvent. Percent by Volume . Also called volume percent or percent by volume, this is typically only used for mixtures of liquids. That's because ethanol and water molecules interact differently with each other than they do with themselves.
Molarity is the number of moles of solute dissolved in one liter of solution .
Molarity is usually denoted with a capital M, i.e. a 0.50 M solution. Also recognize that molarity changes slightly with temperature because the volume of a solution changes with temperature. Molality is the number of moles of solute dissolved in one kilogram of solvent. Notice the two key differences between molarity and molality. Molality uses mass rather than volume and uses solvent instead of solution.