Homework 1-18-11 Freezing Water

1. How much does water expand when frozen? When liquid water is cooled, it contracts as one would expect. Once it reaches an approximate temperature of 4*C it expands slightly until it reaches freezing temperature and then expands by about 9%
2. When is water the smallest? Water is smallest/ most dense at 39*F. It has to do with the molecular structure and the the hydrogen bonds in water. At 39*F water has more room for the molecules to "fill in" the holes created in the lattice. In effect, they occupy the space surrounding the space between the water molecules (Whitcombe, 1999, Chemistry).
3. What happens when salt is added? In the experiment I saw that in the first half hour the salt decreased the rate at which the water was freezing. After an hour and a half the water in all areas, pure, 1/2 teaspoon, 1 teaspoon, and 2 teaspoon were all freezing at roughly the same rate.
4. Does the amount of salt added effect the freezing point? At first the amount of salt added did effect the freezing point, but after a an hour and a half it evened out and continued to freeze at the same rate as the rest of the water. The difference in the temperature also decreased after an hour and a half. The water temperature difference became closer and closer.

                   no salt         1/2 tspn salt       1 tspn salt        2 tspn salt     
1/2 hour         9*C              7*C                  4*C                 4*C
1 1/2 hours    1*C              0*C                  -1*C                -1*C