Homework Assignment 4

I constructed my experiment  by using a plastic ice tray. I filled up a few spaces with only water on one side of the tray. I then used three spaces on the opposite side of the tray with water in each. On the top left of the tray I added one shakes of salt. The middle left spot I put about a teaspoon of salt. On the bottom left I put one shake of the salt. I did this because I wanted to see how dramatic the results would be due to adding salt. Or if there was any difference at all. I made a couple charts documenting the process that I used and how I came to my conclusions. I checked the temperature of the freezer before conducting my experiment and found that it was -10 degrees C which is 14 degrees F. I then tested the water temperature and found that it was 0.5 degrees C which is 32.9 degrees F. I checked the water/ice every 25 minuets five times and then waited until it was completely frozen. These are the two charts that I created to help show the results that I found.

Type of Water	Temperature of Unfrozen Water	Temperature of Freezer	Salt Added	Just Water – No salt added	Expansion of Water without Salt	Expansion of Water with Salt
Right Side	0.5 C (32.9 degrees F)	-10 C (14 degrees F)		Just Water	expanded about 2 cm over edge
Left Top	0.5 C (32.9 degrees F)	-10 C (14 degrees F)	2 shakes of salt			Yes it expanded, slightly over edges
Left middle	0.5 C (32.9 degrees F)	-10 C (14 degrees F)	Several shakes of a lot of salt			Yes it expanded, slightly over edges
Left bottom-	0.5 C (32.9 degrees F)	-10 C (14 degrees F)	1 shake of salt			Yes it expanded, slightly over the edges

Time	Just Water	Top Left (2 shakes of salt)	Middle Left (several shakes of salt)	Bottom Left (1 shake of salt)
5:00 pm	Liquid form	Liquid Form	Liquid Form	Liquid Form
5:25 pm	-2 C (28.4 F) some frozen pieces	-2 C (28.4 F) no freezing	-2 C (28.4 F) no freezing	-2 C (28.4 F) no freezing
5:50 pm	-2 C (28.4 F) more frozen pieces	-2 C (28.4 F) some freezing	-2 C (28.4 F) the least amount of freezing	-2 C (28.4 F) some freezing
6:15 pm	-2 C (28.4 F) mostly frozen	-2 C (28.4 F) mostly frozen	-2 C (28.4 F) more frozen but the least amount	-2  C (28.4 F) most freezing containing salt
6:40 pm	-2 C (28.4 F) mostly frozen	-3 C (26.6 F) thick layer of ice on top to middle	-3C (26.6 F) thick layer on top	-3 C (26.6 F) thick layer of ice on top to middle
7:30 pm	Completely frozen	Completely frozen	Completely frozen	Completely frozen

1. How much does water expand when frozen?
As I researched this question I was able to find that water expands about 9% when it is frozen. This is because the colder the temperature is, the higher the tendency to form hydrogen bonds becomes. When the water reaches the freezing temperature it turns to ice. When this happens it is completely hydrogen bonded. I was able to see this slightly with the water containing salt, but more so with the pure water. I measured about 2 cm of expansion for the pure water.

2. When is water the smallest?
 I could not find anything on the web about this. However I will use my best educated guess in the form of a hypothesis. I believe that water is the smallest when it is not frozen. When water is frozen it expands causing the molecules to slow down. When the water is about room temperature, the molecules can remain active and the water can form to shapes.

3. What happens when salt is added to water?
When I first added the salt to the water it fell to the bottom of the tray. This is because salt is more dense and heavy than water is. My hypothesis before starting this experiment was that the ice would take longer to form with the salt in it. I documented the progress that the ice was making every 25 min. and found that I was correct. The space that I had put the most salt in took the longest to freeze over. I researched this and found that adding salt to the water actually lowers the freezing point, causing it to take longer to freeze than just pure water. When I was doing this experiment I also thought about how we put salt on ice during the winter because it helps melt the ice so that we do not slip and fall. This makes a lot more sense to me now that I have seen it with my own eyes.

4. Does the amount of salt added affect the freezing?
Yes it does. The space that I put the most ice in was the last space to freeze. I believe that this is due to salt causing ice to melt. It then lowered the freezing temperature causing it to take longer to freeze. The more salt added the lower the freezing temperature and the longer the amount of time needed to freeze.