Homework 1/18/11

Water Expansion with Salt Water

I had 3 cups, each filld with 2/3 c of water.  I put the cups outside and I checked them after 2 hours, 4 hours (which I did not put on my graph) and 9 hours.  One was my control which had no salt and froze within 3 hours.  At 2 hours the control was semi-frozen with just some water.  When I checked 9 hours later the water was completely solid and had some bubbles.  It was pretty smooth and had no excess water. 
The second cup I had I put just 1 Tsp in and when I checked it at the 2 hour point the water had started to form slush.  After 9 hours it was semi-frozen and a little more rough than the control cup.  This cup was the warmest cup at this point. 
The third cup I put in 3 Tsp and when I checked it after 2 hrs, it was the coldest of all of the cups.  It however, was barely slushy.  It was the cloudiest looking one, which makes sense.  When I checked it after 9 hours, it looked partially frozen and was very rough looking.  It was also the coldest at this time. 

It was hard for me to scientifically measure if the cups expanded, however I did notice that the control cup did expand after about 3 hours.  However, I could not really tell if the other two expanded. 

When salt is added to water the freezing point decreases.  So that is why the cup with salt was colder, but not frozen.  The more salt, the colder it must be to freeze.  The molecules interfere with one another making it difficult for the elements to freeze together. So yes, the amount of salt affects the freezing point.