The molar mass calculated through colligative properties is sometimes different from that of…

The molar mass calculated through colligative properties is sometimes different from that of experimentally determined molecular mass and is known as abnormal molecular mass. This difference is due to the solute particles that undergo association or dissociation. Consider the two cases given below and answer the questions that follow. (A) The freezing point of a solution containing $5.85\text{ g}$ of $\text{NaCl}$ in $100\text{ g}$ of water is $-3.348^\circ\text{C}$. ($K_f$ of water $= 1.86\text{ K kg mol}^{-1}$, molecular mass of $\text{NaCl} = 58.5$) (B) The freezing point of benzene solution decreases by $0.45^\circ\text{C}$ when $0.2\text{ g}$ of acetic acid is added to $20\text{ g}$ of benzene. ($K_f$ of benzene $= 5.12\text{ K kg mol}^{-1}$, molecular mass of acetic acid $= 60$) Calculate the abnormal molecular mass of solute in both the cases.