Cool Science Trick: Instantly Freeze Water

My first podcast is below! It was harder for me to figure out how to record this baby than to do the experiment! In it, I explain how to instantly freeze water. I also made a video! Listen, watch, or read! Or do all three!

How I felt at first, diving into the world of podcasts

It’s easy to instantly freeze water and it doesn’t involve the freezer. That’s too unreliable. I’ve tried several methods and this one works.

I’m betting that you already have what you need around the house!

Now comes the fun part for me. Explaining not just how to do this, but why it works.

Sorry I can’t help myself!

my bad

Supercooling or superfreezing a liquid means that you chill the liquid below its freezing point without it becoming a solid. We all have access to water, so it’s the perfect liquid to work with!  Once the water is chilled below it’s freezing point, we can trigger it to instantly freeze before our eyes! Okay, let’s go!

Here’s what we need:

  • Large bowl
  • Water bottles
  • Ice
  • Thermometer
  • Watch/timer
  • Salt
materials needed to supercool water

Here are the steps:

  1. Fill your bowl with ice and put it on the table or counter. Somewhere that you don’t need to move it around once you start.
  2. If you’re impatient (like me!) add some water, to get the ice melting. You should have two to three times as much ice as water. For the large bowl in the picture, I used about eight cups of ice and two of water.
  3. Add about a cup of salt. I used Kosher salt because it’s more coarse, but table salt works.
  4. Put your thermometer into the ice bath. Let it cool down for about twenty minutes. (Cool down, you ask? But it’s ice! I’ll explain in just a sec…)
  5. When the temperature in the icy bath reaches 25 degrees F, add the water bottles.
  6. Let the water bottles cool down for about 20 minutes, undisturbed.
  7. When the temperature reaches 16 degrees F, you are ready to roll.
  8. CAREFULLY take your water bottle out. Twist open the top. Slam it on the table.
  9. Instant ice!
Question mark
What’s going on here?

We learned in school that ice freezes at 32 degrees F. (or 0 degrees Celsius) The more complex concept is that the freezing or melting point of a substance is actually the temperature at which the liquid and solid phases are in equilibrium.

For pure water, this means that ice is melting at exactly the same rate that liquid water is freezing. At 32 degrees F or 0 degrees C.

 

Chemical equilibrium is an important concept. Nature loves an equilibrium!

Equilibrium

What we’ve created with that icy salt bowl is a perfect equilibrium for the bottled water!

Moving on.

For the water to freeze completely to ice, it needs something to freeze on to. These are called ‘nucleation sites.’ 

Any small impurity will work. So do vibrations! That’s why we hit the bottle on the table, to begin the crystallization. Chemistry gets it way, and a new equilibrium is established with the solid ice!

What about the salt, you ask? Good question!

The salt in the bowl interferes with the chemical bonding needed to form a solid (in this case ice). So the salt is lowering water’s freezing point. Salt is composed of sodium and chlorine. The water molecules tend to stick to the salt ions in solution instead of to each other, and the water doesn’t freeze.

And this is why we sprinkle salt on our sidewalks and driveways in the winter. The salt interferes with the water molecules lining up and ice does not form.

picture of sodium chloride

In fact, our salty oceans freeze at around 28.4 degrees F because of the salt! 

glacier

But without a nucleation site and if the water stays very still, you can keep cooling the water well below 32 degrees F (0 C) . This condition is known as ‘supercooled.’ Under the right conditions, water can stay liquid until it reaches -40 degrees Celsius.

 

Give this a try! Please let me know how it goes. Feel free to contact me for troubleshooting!

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Susan Berk Koch
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