Question

1. Consider the structural formulas of your solute and the TBA and discuss why the solute is

soluble in this solvent.

2. Discuss why the temperature remains constant while a pure liquid freezes.

3. Discuss why the temperature drops while a solution freezes.

4. Discuss which measurement will be the least accurate in this experiment.

5. The TBA vaporizes somewhat during the various runs. What effect does this evaporation have
upon the determined molar mass? (Consider whether the calculated result is a molar mass that is

too high or too low.)

Answer 1

More info is requiered. Those questions seems from some lab experiment where you do have a particular solute.

1) TBA is tertbutyl alcohol. and is very apolar for an alcohol. Which solute do you have?

2) Pure liquids freeze/melts while T is constant. That's because all the energy taken/given to the system in the freezing/melting point is used for the change of phase and not to change the kinetic energy of the molecules (change in temperature). Once pure liquid is totally frezee, temperature drops.

3) Because once the solution star to freeze, solute concentration in the liquid increases changing the freezing point gradually.

4) Measure freezing point while freezing is more difficult to measure than while melting. It's easier to control the heat addition than the heat extraction.