 So, let's talk about abnormal molar masses in this video. You see, when you have compounds like KCl or NaCl and you dissolve it in water, the ionic compound would completely dissociate into its constituent ions. In this case we would get K plus and Cl minus ions. So that means if we dissolve one mole of KCl, we would get one mole each of K plus and Cl minus ions. So as a result, in the solution we have two moles of particles. Now why is this significant? Well, this is important because collicative properties depend entirely on the amount of solute particles or the number of solute particles in the solution. For example, when one mole of KCl is dissolved in 1 kg of water, then the expected increase in the boiling point is 2 into 0.52 K. Now this value of 0.52 K refers to the boiling point elevation constant for water. And it tells us how much the boiling point of the solvent in this case water would increase for each molal increase in the concentration of the solute. So here we have 2 into 0.52 K, right? And this is the total increase in the boiling point for one molal solution of KCl in water. But this increase in the boiling point would be same as the increase in boiling point when we would have two moles of a non-dissociating solute. For instance, if we had two moles of sugar, we would get that same increase in the boiling point as we got in the case of one mole of KCl. Now the problem here is that if we did not know about the degree of dissociation of KCl, we would calculate its molar mass wrongly. Now because the increase in the boiling point here corresponds to two moles of particles, we would calculate the molar mass of KCl as if it were formed from two moles of particles. That is, we would be tempted to conclude that as mass of two moles of particles is 74.5 grams, mass of one mole of KCl would be 37.25 grams. So from here we can see that whenever we have dissociation of solute particles, the experimentally obtained molar mass is always lower than the actual value of the molar mass. In this case, the experimentally obtained molar mass of KCl would be 37.25 grams whereas the actual molar mass value is 74.5 grams. So we can obviously assume that the exact opposite happens in the case of association. Now in the case of association, for example let's take a molecule that associates, yeah, acetic acid in a nonpolar solvent like benzene. Two molecules of acetic acid would combine with each other in a nonpolar solvent like benzene to form a dimer as you can see here. So the dotted lines that you see here are the hydrogen bonds formed between the acetic acid molecules. Now if all the acetic acid molecules associate or combine to form a dimer like this, then in the solution we have only half the number of the solute particles, right? Because two acetic acid molecules combine to give one dimer. That means the increase in the boiling point would also be half of what we would normally expect. So experimentally you will get the molar mass of acetic acid as a molar mass value of the dimer which is about 120 grams per mole. But the actual molar mass value of acetic acid is only half of it. In other words we can say that when we have association of solute particles, the experimentally obtained molar mass value would always be greater than the actual value. And this is what we refer to as the abnormal molar mass. And to account for this abnormality that arises due to association or dissociation of solute molecules, vanthoff introduced a term known as vanthoff factor. It is denoted by I. So let's learn about vanthoff factor and how it modifies the equations of colligative properties in the subsequent videos.