$($a$)$ Dichloromethane, acetone, and methanol are strongly polar fluids; their molecules

have appreciable dipole moments. At $25C,$ the following activity coefficients $($at in$-$

finite dilution$)$ were measured by Smith et al$.(1983,$ J$.$ Chem. Eng. Data, $28$: $412)$ in

binary solutions:

These data show that binary mixtures of dichloromethane$/$acetone exhibit appreciable

negative deviations from Raoult's law. However, the data for binary mixtures of di$-$

chloromethane$/$methanol exhibit large positive deviations. Why is there such a strik$-$

ing difference between these two binary systems?

$($b$)$ At $50C,$ we have data for the activity coefficient of nitroethane in benzene and in

hexane. When the mole fraction of nitroethane is $0\mathrm{.}05,$ is the activity coefficient of

nitroethane larger in benzene or in hexane? Explain.

$($c$)$ Near room temperature, we want to dissolve a heavy, aromatic, coal$-$derived liquid in

a volatile solvent. Two solvents are considered: methanol and chloroform. Which

solvent is better; that is$,$ in which solvent is the solute likely to be more soluble?

Why?