question_answer

  Why is the mass determined by measuring a colligative property in case of some solutes abnormal? Discuss it with the help of Vant Hoffs factor.                                                                                                     (Value Based)

Answer:

  Certain compounds when dissolved insuitable solvents either dissociate or associate. For example ethanoic acid dimerises in benzene due to hydrogen bonding while in water, it dissociates and forms ions. As a result the number of chemical species in solution increases or decreases as compared to the number of chemical species of solute added to form the solution, Since the magnitude of colligative property depends on the number of solute particles, it is expected that the molar mass determined on the basis of coelegative properties will be either higher or lower than the expected value or the normal value and is called abnormal molar mass. In order to account for the extent of dissociation or association of molecules insolution, Van't Hoff introduced a factor i, known as the Van't Hoff factor. It can be denned as follows :                                                                      1                                                                   1