Discussion
You will need: Four bottles of very pure water, distilled water is best One bowl A freezer Lots of patience – this can be a difficult experiment to reproduce! Take the labels off the bottles of water.
2 Place the bottles in a freezer and leave undisturbed for at least 30 minutes. Check on the bottles regularly!
3 As soon as one looks like a bottle is forming ice crystals, gently remove them from the freezer.
4 Shake one of the bottles and watch the ice crystals form instantly!
5 Try stirring one of the bottles with a straw, or perhaps adding a piece of ice or dirt to the solution.
6 Try carefully pouring the supercooled water into the bowl over an ice cube… you’ll form an ice stalagmite!
Why Does This Happen
Ice generally forms on microscopic scratches and bumps called nucleation sites. Nucleation sites, or ‘bumps’, occur within most containers with imperfections – even dissolved impurities such as calcium or even air bubbles act as nucleation sites for ice to form. If you remove the nucleation sites from the water, the water cannot form ice crystals easily.
Normally, pure water (without impurities) will form ice crystals at 0 degrees Celsius or lower.
However if pure water is cooled down very slowly, in a very smooth container with no dust inside, you can make water stay a liquid at temperatures below zero. Supercooled solutions are very unstable. Introducing air bubbles or a seeding crystal into the solution causes the liquid water to rapidly freeze.
Be aware that supercooling is different from freezing point depression. Freezing point depression occurs when you dissolve an ionic solid such as salt in water. A saltwater solution will have a lower freezing point than pure water – do the experiment and find out for yourself!
Take the labels off the bottles of water.
2 Place the bottles in a freezer and leave undisturbed for at least 30 minutes. Check on the bottles regularly!
3 As soon as one looks like a bottle is forming ice crystals, gently remove them from the freezer.
4 Shake one of the bottles and watch the ice crystals form instantly!
5 Try stirring one of the bottles with a straw, or perhaps adding a piece of ice or dirt to the solution.
6 Try carefully pouring the supercooled water into the bowl over an ice cube… you’ll form an ice stalagmite!
Why Does This Happen
Ice generally forms on microscopic scratches and bumps called nucleation sites. Nucleation sites, or ‘bumps’, occur within most containers with imperfections – even dissolved impurities such as calcium or even air bubbles act as nucleation sites for ice to form. If you remove the nucleation sites from the water, the water cannot form ice crystals easily.
Normally, pure water (without impurities) will form ice crystals at 0 degrees Celsius or lower.
However if pure water is cooled down very slowly, in a very smooth container with no dust inside, you can make water stay a liquid at temperatures below zero. Supercooled solutions are very unstable. Introducing air bubbles or a seeding crystal into the solution causes the liquid water to rapidly freeze.
Be aware that supercooling is different from freezing point depression. Freezing point depression occurs when you dissolve an ionic solid such as salt in water. A saltwater solution will have a lower freezing point than pure water – do the experiment and find out for yourself!
Variables to test
More on variables here
Try salty vs freshwater. What happens if you rapidly heat up the super-cooled water in the bottle?
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