So Coo, it is supercool
You can use your freezer to produce supercooled water which will crystallize when touched by a snowflake.
Stretch the plastic wrap over the mouth of the bottle so that it is tight and smooth.
To Do and Notice
Fill the eye dropper with water.
Place 6 drops of water about 0.5 to 1 cm in diameter on the stretched plastic.
Place the container with the drops in the freezer.
Start the stopwatch.
Check on it every minute until at least one of the drops has frozen.
Note the time for future experiments.
Quickly take it out of the freezer and place it on a table.
Touch a liquid drop with a piece of ice, watch it freeze!
What's Going On?
The water drops cool in the freezer until their temperature is below freezing.
If there is an impurity in the water then it can act as a seed crystal and cause one entire drop to freeze. So one drop is likely to freeze first while the others are still below freezing
If a drop of supercooled water is touched by an ice crystal this seed crystal will cause it to freeze.
If the water is cooled below -60°C it will freeze even in the absence of a seed crystal, this is called the homogeneous nucleation temperature.
Take a small plastic bottle of sugar free carbonated water.
Place it in the freezer.
Take it out after 10 minutes and open the bottle. Notice whether it freezes or not.
Experiment with other bottles to find the time it takes them to supercool in your freezer so that when you open them they freeze.
Sometimes in the atmosphere water drops supercool. When they hit a tree, the ground or anything the object acts as a seed crystal and the water freezes on it.
The result is called freezing rain.
Scientific Explorations with Paul Doherty
2 December 2006