I'm really bad at chemistry, but I was wondering about this the other day as I was filling up my ice tray. Freezing Point Depression is a well-known colligative property of liquids when a solute is added- for example, salt. It depends on the molar concentration of the solution (and an unimportant constant, for this discussion). If I dissolve salt in water, it freezes at a lower temperature depending on how much salt I can dissolve in a given volume. But in this case doesn't the molar concentration change as more water freezes? I seem to remember something about how the solute doesn't freeze along with the water, in which case the volume would decrease with a corresponding increase in concentration. What am I missing here? I'm sure it's simple, but as I said... chemistry isn't my thing. Any enlightening information would be greatly appreciated.