Explain abnormal molar masses.

(N/A) Abnormal molar mass refers to the molar mass of a solute that is either lower or higher than the expected or normal value,calculated based on colligative properties.
$1$. Dissociation: When ionic compounds dissolve in water,they dissociate into cations and anions,increasing the number of particles in the solution. For example,$KCl$ dissociates into $K^{+}$ and $Cl^{-}$ ions. Since colligative properties depend on the number of particles,the observed effect is higher than expected,leading to a lower experimentally determined molar mass compared to the theoretical value.
$2$. Association: Molecules may associate to form larger units,reducing the total number of particles in the solution. $A$ classic example is the dimerization of acetic acid $(CH_3COOH)$ in benzene due to hydrogen bonding,as shown below:
$2 CH_3COOH \rightleftharpoons (CH_3COOH)_2$
In this case,the number of particles is reduced,resulting in a lower observed colligative property value and a higher experimentally determined molar mass compared to the theoretical value.