Useful Sites

http://www.worsleyschool.net/science/files/saltandfreezing/ofwater.html - explains about what happens to the molecules in the water during the freezing process.

http://www.newton.dep.anl.gov/askasci/env99/env133.htm - explains about ions in the water, info about crystal formation during the freezing process.

http://www.scienceproject.com/projects/intro/primary/PX071.asp - project.

http://en.allexperts.com/q/Oceanography-2135/salt-water-freezing-1.htm - explains from a chemistry-ish perspective why the salt water lowers the melting and freezing temperatures of the water.

http://www.picotech.com/experiments/freezingofwater/freezingofwater.html - experiment info.

Variables for Saltwater/Pure Water Experiment

If I were to go ahead with the freezing of saltwater vs pure water experiment, the variables would be as follows:

Independent Variables:
1. Amount of time in freezer
2. Quantity of water
3. Temperature of water
4. Salt/sugar/vinegar/nothing in water
5. Temperature of freezer

Dependent Variables:
1. How quickly the temperature drops
2. How quickly each of the cups of water freezes

Experiment - Using Water, Sugar, Salt and Vinegar

I think what would be best would be to do an experiment to investigate which of the following slows down the freezing of water best - sugar, salt or vinegar.

Just discovered this site - http://www.picotech.com/experiments/freezingofwater/freezingofwater.html.

It gives an example of an experiment used to test the freezing of salt water compared to the freezing of pure water.

The problems with the experiment on the website are:
1. The equipment listed is very complicated/unattainable - e.g. "DrDAQ DataLogger". BUT wouldn't a thermometer do the same thing?
2. Because of changing the equipment the experiment would be more confusing/difficult.

The other thing to consider would be how often to measure the temperature. Measuring would also have to be done very quickly in order for the results to not be affected by the room temperature.

Experiment Method I would use if I conducted this experiment:
1. Fill 4 plastic cups with plain tap water, water with sugar mixed in, water with salt mixed in and water with some vinegar in it.
2. Place each cup in the same freezer.
3. Measure the temperature of the solutions at specified intervals.
4. Record results.
5. Repeat experiment several times.

Salt/Sand

More on the idea of salt melting sand/preventing it from freezing.

According to http://van.physics.illinois.edu/qa/listing.php?id=1580, salt lowers the melting and freezing point of water.

This also means salt water will freeze more slowly than regular water. Maybe it would be better to do an experiment concerning salt and the freezing point of water than salt preventing sand from freezing.

Other sites also stated that, when water is frozen, the molecules lose energy and come closer together to form the hydrogen bonding required to form ice. However, when salt (an impurity) is in the way, the molecules need to lose more energy.

Ideas

1. Quick assessment of danger as related to age.

Best way to do this might be using photos. Saw something on the ABC once which was similar. People of various ages sorted pictures into dangerous/not dangerous piles and apparently teenagers got most many of them wrong. Lots of background research on that one. Not consistent enough?


2. Evaluate how much salt is needed to keep sand from freezing.

Saw something once about truck drivers in the US who, for some reason, were driving sand halfway across the country in freezing weather and their sand kept freezing. Apparently salt fixes this. Did some research and some people said 5% salt, some 50%. Could use different types of salt as well (some people suggested Potassium Chloride, some Calcium Chloride etc.).


3. If all else fails, generic "does music affect plant growth?" experiment is always available.