When we add ethylene glycol to automobile radiators
as an antifreeze, we are
taking advantage of the freezing point lowering of the
radiator water. Ethylene glycol evaporates too readily
in the summer months, but with other less volatile "year-round"
antifreezes, we also make use of the raising of the
boiling point of the radiator water to prevent
boilover in hot weather.
When we scatter salt on icy sidewalks, Na+
and Cl- ions
lower the freezing point of water and cause the ice
to melt into a concentrated brine.
Similarly, home ice cream makers use rock salt and ice
to produce a slush at a lower temperature than can be
achieved with pure water and ice.
All of these are applications of the colligative
properties of molecules and ions dissolved
Another important application of colligative properties
is in determining molecular weights.
A freezing point depression measurement can tell us
how many moles of a solute are present, and if we already
know the number of grams, it is easy to calculate the