Homework 1-18-11

How much does water expand when frozen? 9%  Density of water is 1.0 g/mL and density of ice is 0.92 g/mL Water is more dense than ice.  This is why ice cubes float and lakes freeze from the top.  I could not have a good experiment with the expansion at home as I don't feel I have adequate tools to do the experiment.  I could put water in a measuring device and measure how much it rises up but that would not give me the expansion outward. 

100 g x	1.0 mL =	108.7 mL
	0.92 g

When is water the smallest? Temp?
After the water was outside about an hour the water line went down just a little then it began to go up as it started to freeze. Water is the smallest at 3.98C or 39.16 F  At this temperature the water molecules are the closest together.  When they are colder they start to move farther apart. 

What happens when salt is added to the water?
The temperature of the water is lowered.  It takes longer for water to freeze when you add salt to the water.
I put 100ml of water into three different cups.  I added 2 tsp of salt to one cup and 1 Tbp to the last cup the last cup was just the water.  After three hours the cup with only water was frozen solid.  The cup with 2 tsp of salt was not completely frozen but very close.  The cup with 1 Tbp of salt was slushy and not solid. 

Does the amt of salt added affect the freezing point?
Yes, the freezing point changes when you have salt added and the more salt added the lower the temperature has to be for the water to freeze.

Why does water expand when it freezes?

The normal pattern for most compounds is that as the temperature of the liquid increases, the density decreases as the molecules spread out from each other.  As the temperature decreases, the density increases as the molecules become more closely packed.  This pattern does not hold true for ice as the exact opposite occurs.  In liquid water each molecule is hydrogen bonded to approximately 3.4 other water molecules.  In ice each molecule is hydrogen bonded to 4 other molecules.