Скачать или смотреть XIIChemistrySolution-Abnormal molar mass,i-Factor,Degree of dissociation/ association & numerical

By Er. Deepak Kumar (Live Interaction Class)
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We know that ionic compounds when dissolved in water dissociate into cations and anions.
For example, if we dissolve one mole of KCl (74.5 g) in water, we expect one mole each of K+ and Cl– ions to be released in the solution. If this happens, there would be two moles of particles in the solution. If we ignore interionic attractions, one mole of KCl in one kg of water would be expected to increase the boiling point by 2 × 0.52 K = 1.04 K.
Now if we did not know about the degree of dissociation, we could be led to conclude that the mass of 2 mol particles is 74.5 g and the mass of one mole of KCl would be 37.25 g. This brings into light the rule that, when there is dissociation of solute into ions, the experimentally determined molar mass is always lower than the true value.
Molecules of ethanoic acid (acetic acid) dimerise in benzene due to hydrogen bonding. This normally happens in solvents of low dielectric constant. In this case the number of particles is reduced due to dimerisation. Association of molecules is depicted as follows:

Definition-
A molar mass of a substance determined by studing any of the colligative properties come out to be either lower or higher than the expected or normal value is called as abnormal molar mass.