Homework 1-18-11

How much does water expand?

Water is at a different density depending on the temperature. The relation between temperature and density is not linear. It expands as it gets less dense. It does this because it has to become less dense to expand; it only has so much matter. It also expands because the molecules are moving faster because they are warmer. By moving faster they bounce on the outside of the molecule faster and push outwards on it, making it larger.

Density of liquid water

Temp (°C)	Density (kg/m3)[17][18]
+100	958.4
+80	971.8
+60	983.2
+40	992.2
+30	995.6502
+25	997.0479
+22	997.7735
+20	998.2071
+15	999.1026
+10	999.7026
+4	999.9720
0	999.8395
−10	998.117
−20	993.547
−30	983.854
The values below 0 °C refer to supercooled water.

When is water the smallest?

At 4C water is the most dense. As you can see in the chart above it begins to expand to a gas as it gets warmer, and expands to a solid as it gets colder. When I froze the water I froze cold and hot water because I have heard hot water freezes faster and cold water boils faster. When my hot water froze it stayed at the same level in the cup, but my cold water froze and the level rose showing that it expanded. I think the hot water was less dense than the cold water, so when i froze it the level went down first and then up to its original level. Whereas the cold water was more dense at first so the level didn't go down as much before it went up, and thus had a higher level in the end.

What happens when salt is added to the water?

Adding salt lowers the freezing point of water. The salt is taking heat from the water to dissolve so the boiling point would also go up.

Does the amount of salt added affect the freezing point?

 The more salt, the more heat that would be required to dissolve it, so yes. 

No salt	salt	tons of salt
15	15	15
0	3	4
-4.5	-5	-5

I found that at first my no salt got colder sooner, with the saltiest getting colder the slowest. It would have more heat in it because of all of the dissolving salts, and so it would get colder slower. The one with no salt got colder fastest because it didn't have the salt  pulling in heat.