Question

Suggest at least 3 solutes for each of these solvents that shows the maximum freezing point depression in their solution after mixing them. Solvents: Water, Acetone, Heptane, Toluene

Answer 1

Suggest at least 3 solutes for each of these solvents that shows the maximum freezing point depression in their solution after mixing them. Solvents: Water, Acetone, Heptane, Toluene.

1. Water: Nacl (common salt), Sugar, Ethylene Glycol
2. Acetone: Benzene, Dry ice (CO2),
3. Heptane: cyclohexane, octane, higher alkanes
4. Toluene: Naphthalen, Benzene, biphenyl compounds, anthracene

The freezing point is the temperature at which solid and liquid can simultaneously coexist, meaning that the escaping tendencies of molecules from the two phases is the same. Suppose now that we dilute the solvent by adding some solute. The escaping tendency of solvent molecules from the liquid phase is now reduced owing to their increased disorder in the solution, but in the solid nothing has changed and the escaping tendency of solvent molecules from this phase remains the same. This means that there will be a net movement of solvent molecules from the solid phase to the liquid; the solid melts. In order to keep the solid from melting, the escaping tendency of molecules from the solid must be reduced. This can be accomplished by reducing the temperature; this lowers the escaping tendency of molecules from both phases, but it affects those in the solid more than those in the liquid, so we eventually reach the new, lower freezing point where the two quantities are again in exact balance and both phases can coexist.