Praxis: Ice in an instant
By Medicine Hat News on March 31, 2018.
Do not forget that tomorrow is April Fool’s Day! This is one of my absolute favourite days of the year. Who doesn’t love a day that you can play pranks on people? Of course, a prank involving science is even more fun! Let’s get started. *Remember to ask an adult before doing this experiment. Materials – bowl – ice – pickling salt – 500 mL plastic bottle of distilled water unopened – counter – thermometer Procedure 1. Fill a bowl with ice. Sprinkle salt over the top. Mix well with your hands. You want to get the bowl of ice melting and starting to get very cold. The addition of salt will speed this up for you. 2. Place the bottle of water in the ice and salt mixture. Make sure the bottle is surrounded by ice. It is important that the bottle of water get chilled as well as it possibly can. 3. Place the thermometer in the ice and salt mixture. 4. Keep checking the temperature of the ice mixture approximately every 10 minutes. You will need to watch this closely as there will be a fine line between too cold and just cold enough. 5. Add ice and salt as the mixture begins to melt. Keep the bottle of water submersed in this mixture. 6. When the thermometer reaches -5 C gently remove the bottle from the mixture. Observe (quickly). 7. Hit the bottle against the counter quite quickly. 8. Observe. What is going on? You should have observed the bottle was liquid when you removed it from the salt and ice mixture. When you hit it against the counter, it should have turned into ice instantly. How does this happen? Magic? An April Fool’s trick? No, science! The answer lies in the science behindthe freezing temperature of water and how icecrystals form. We all know that the freezing point of water is 0 C. In making a mixture with the salt and ice, we were able to “supercool” the pure or distilled water to a level that is below the normal freezing point of water. Water normally freezes at 0 C when it is not pure because it has something to “grow” on or impurities in the water. These may be minerals or small particles of dirt, but it is something for those crystals to attach to and start growing. In the pure water, there is nothing for the crystals to attach to and start growing. Ice only forms when you “disturb” the water molecules in your bottle. As you hit the bottle on the counter, you are generating energy. This energy forces the supercooled water molecules to form crystals and look frozen through a process called nucleation. Try this experiment with other liquids to see what happens! Patty Rooks is senior scientific consultant at PRAXIS, “Connecting Science To The Community.” Contact Praxis at praxis@praxismh.ca, http://www.praxismh.ca, Tweet or follow us @PraxisMedHat, or friend us on Facebook. 24-23
