I am having doubts about what B&B say in section 28.6 about the "ebullioscopic" and "cryoscopic" constants. That is, they seem like a nice shortcut to do Problem 7 ii). The problem is that the units don't work out. x_B is dimensionless, so the kg^-1 in the denom of the ebullioscopic constant can't be correct.
There are lots of references on the Web on depression of freezing point of water. Many pitch this in terms of the moles of solute per kg of water; not x_B which is a dimensionless number between 0 and 1.
Anyone want to agree or disagree? Also, I got a huge reduction in the freezing point with x_B = 0.22. Maybe one should redo the problem with x_B = 0.02 :-)