When water freezes, it loses energy and transitions from a liquid to a solid state at a certain temperature. When salt water freezes, the freezing point is lower than pure water due to the salt ions interacting with water molecules. More heat must be lost from the salt water solution before it freezes compared to pure water, resulting in a greater decrease in temperature from the initial state to the frozen state.

1. Prelab questions Initial model Based on your understanding, describe and/or represent what is
occurring when water a pure solvent, is freezing and compare it to the freezing of a salt water
solution. Describe what you expect to observe on the macroscopic level (see, hear, feel, smell)
and what is occurring on the molecular level (explain using words/pictures what you think the
molecules, atoms, and/or ions are doing that results in your observations) at the following stages:
(a) before the solvent/solution starts to freeze; and (b) after the solvent/solution is frozen.
Molecules, atoms, and ions can be represented with symbols. If you use symbols, be sure to
provide a key.
Solution
Freezing point depression
When water a pure solvent is frozen from liqid to solid state, it looses energy. The final solution
is cooler than the initial solution of pure solvent.
When salt solution in water is frozen, the final solution temperature is now much lower than the
final temperature achieved by pure solvent water only. therefore, greater amount of heat is lost in
this case. Solution gets more cold than the initial conditions and when comapred to pure solvent
water final freezing point temperature.