Michael
Posts: 47
Joined: Mon Nov 12, 2007 8:08 am
Occupation: Student: 11th Grade

Science Experiment

Postby Michael » Sun Nov 25, 2007 7:17 pm

I think I wasn't clear and decided to re-state my research. I would be grateful for any other comments and if you think I've supported my hypothesis enough.

Hypothesis: "My prediction is as the amount of salinity increases in the water, the water will expand less."

Research to Back Up Hypothesis:

- As your add salt to water, the salt slows down the molecules from expanding and freezing.

- As you add salt to water, the density of the water increases. A lower temperature is required to freeze the salt water.

- When water freezes, the molecules start holding on to each other tightly. This creates a pattern that actually takes up more space than when they were a liquid. This pattern forms a hexagonal structure like a snowflake. This allows air space in the structure and creates space in the structure and the air make the ice light. So, when water freezes, the molecules take up more space causing the ice to expand larger than the water was.

- When salt water freezes, tiny platelets and needles of ice form over the surface of the liquid. The ice crystals incorporate water, but tend to leave the salt behind. So, the solution becomes saltier and saltier as the freezing process continues. The salt is excluded because salt has a different crystalline structure. It forms cubic crystals (with 4 sides) whereas ice is hexegaonal )with 6 sides.

- The 6 sided ice crystals build one on another to form sheets of ice. When salt (sodium chloride) is mixed into the water, chlorine ions grab the hydrogen atoms in H2O that interferes with the ice crystal building. It's difficult then for the ice crystals to connect and so they move slower to freeze.

paulsdecarli
Former Expert
Posts: 67
Joined: Sat Sep 03, 2005 10:20 am

Freezing salt water

Postby paulsdecarli » Mon Nov 26, 2007 12:01 pm

Water is a very strange liquid, about which whole books have been written. I think you need to read more about water before doing any experiments.
In particular, I'd read about the freezing of sea ice.

A few facts about water. Water is one of the few liquids that becomes less dense when it freezes. Water is at its most dense at a temperature of 4 degrees C. When cooled below this temperature it expands. Most other liquids become progressively denser as they are cooled.

I'd read about hydrogen bonding of water molecules, too.

One thing that impresses me most when I am a Science Fair Judge is the research report. If a student writes a good review of the subject, then the student probably will have learned enough to interpret the results of the experiment. To me, the Judge, the most important thing is for the student to learn something new. If the experiment didn't work as originally planned, but the student understands why it didn't work, it was a good experiment.


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