The key difference between a 1.0 molar solution and a 1 molal solution is that a 1.0 molar solution has one mole of solute dissolved in the solution whereas a 1 molal solution has one mole of solutes dissolved in one kilogram of solution.
Long ago, Avogadro hypothesized that there is a specific number that represents the number of atoms or molecules in one mole of a substance. Thus, one mole of each element contains an equal number of atoms, irrespective of the atomic weight of that element. As a result, the concepts of molarity and molality were also developed to describe concentrations of a solute in a solution. While molarity is the measure of a number of moles of the solute in a litre of solution, molality is the number of moles in 1kg of the solution. Hence, it is easy to find out the difference between a 1.0 molar solution and a 1 molal solution.
