Approximate Time to Complete: 1-2 Hours + Questions & Journal Time
- 4 or more 8oz (30mL) plastic water bottles. They must be purified water (NO ADDED MINERALS)
- Tap water
- Ice cubes (5-10 lbs)
- Table salt (1-3 cups)
- Metal bowl
About This Activity
This experiment can be an exciting way to dive deeper into the concept of phase changes that you learned in Different Properties at Different Temperatures. We just added new nomenclature cards on phase changes too! You can access them in our Online Classroom.
- How to supercool water.
- What “supercooling” means.
- How impurities can change the way water freezes.
- What are some of the differences between liquid particles and solid particles?
- What do you need in order to turn water from liquid to solid?
- At what temperature does water freeze?
- How long does it take for water to freeze?
Before you begin, put your “patient pants” on. This experiment can be very particular and may take a couple of tries. Trust us though, when you finally get it, the excitement is worth it!
Part 1: The Set-up
- Empty one of your water bottles, fill it with tap water, and close the lid. Label it so you don’t forget which one it is!
- Fill your metal bowl halfway with ice.
- Place the tap water bottle and 4 or more purified water bottles on top of the ice. *The more purified water bottles you supercool, the more tries you will get in parts 2 and 3 (below).
- Add more ice to the bowl to cover the water bottles.
- Pour water over the ice until it fills the bowl about ¼ of the way.
- Pour a layer of salt over the ice cubes.
- Insert your thermometer into the bowl, and wait until the thermometer reads between 16 °F and 19 °F (-9 °C and -7 °C).
- Set your timer for 45 minutes. Add ice and salt throughout to keep the temperature between 16 °F and 19 °F (-9 °C and -7 °C).
- After 45 minutes, the tap water bottle should be partially frozen. Once the tap water is partially frozen, the purified water bottles should be supercooled (they’ve been cooled below their freezing point, but still liquid). If the tap water is not partially frozen, set a timer for 5 more minutes and repeat until it is. Please note, if you use water bottles that are more than 8 oz, you will have to leave them in for longer. Using bigger bottles could be a fun extension experiment to set up!
Part 2: Instant Ice in a Bottle
- CAREFULLY take one of the purified water bottles out of the bowl, and hit it on the counter a few times.
- Ice crystals should start to form in the bottle. If they do not, put the bottle back in the ice bath, and set the timer for 5 more minutes. Repeat this step with 5-minute increments until your purified water bottle forms ice crystals when you hit it on the counter. It comes in handy to have many bottles to test!
- If all of the purified water bottles are already frozen, they were in the ice bath for too long, and you will need to try again. You can use different bottles, or wait until your frozen bottles are back to room temperature.
- Try hitting a bottle of cold sink water on the counter, or cold water from the refrigerator, does it form ice crystals?
Part 3: Instant Ice Tower
- You’ll need one of the supercooled, purified water bottles from part 1 that is still liquid.
- Put an ice cube onto a plate or in a bowl.
- CAREFULLY open the cap of your supercooled water bottle.
- Pour the supercooled water onto the ice cube. The water should turn to ice the second it touches the cube.
- Try doing this with cold sink water, or water from the refrigerator, does it immediately turn to ice when it touches an ice cube?
Questions & Further Research
Use these questions as a guide to write a journal entry, make a poster, give a presentation, or write a research report about your experiment or a related topic.
- How long did it take to supercool your water bottle to the point where it could form ice?
- What does “supercool” mean?
- Go back to the questions from the beginning – would you change any of your answers?
- Which takes longer: water turning to ice, or ice turning to water?
- Test other liquids to see if they have the ability to supercool as water does.
- What properties do you think a liquid needs to have in order to be able to supercool?
How it Works
Imagine you’re building a card house. One by one, you stack each card in a perfect pattern to build a giant structure. It takes A LOT of time and energy.
Then, your friend comes over and knocks it down. That didn’t take very much energy.
The cards are like H2O (water) molecules. Making a cardhouse out of the cards is like freezing water molecules into ice. Knocking a cardhouse down is like melting ice.
Water particles are liquid. They cling closely enough to touch each other, but they’re free to move around. Ice particles on the other hand are very rigid. They stay near each other in an organized pattern (like the cardhouse).
In order to go from ice to water, you only need a little bit of heat energy. You can break apart the organized structure of ice by raising the temperature above 32 °F (0 °C). If you put a piece of ice out on the counter, it will immediately start melting.
In order to go from water to ice, it takes more energy. It takes more energy to organize particles than it does to break them apart – just like how it took more energy for you to make your card house, and less energy for your friend to knock it down.
If you lower the temperature of water below 32 °F (0 °C), the water will cool and cool until FINALLY it has enough energy to start organizing into ice crystals. Then, the rest of the water will turn to ice very quickly. Just before any ice crystals form, we say that the water is “supercool.” The water is colder than it’s freezing point, but it is still liquid.
You could do this in the freezer, but using the salty ice bath method helps it happen more quickly … can you think of why that might be?
Here’s a hint, it has to do with freezing point depression.
In part 2 of this experiment (Instant Ice in a Bottle), you try to catch the water right before the first molecules organize themselves. Then, you can give them some extra energy by hitting the bottle on the counter. That extra energy helps the molecules move around and get into a perfect position to start organizing into ice.
In part 3 of this experiment (Instant Ice Tower), you use an ice cube as a seed crystal to start the freezing process. When the supercooled water hits the ice, the water molecules immediately align themselves with the organized, frozen water molecules in the ice cube.
You seem to have made “instant ice.” However, you just waited until right before ice formed on its own, and gave it a little extra “oomf.”
The reason that the tap water freezes has to do with the minerals in it. The minerals in tap water give the water molecules something to cling to and start building ice crystals off of. Kind of like how you used an ice cube as a seed crystal in part 3 of this experiment. It doesn’t need as much time or energy as purified water to form ice crystals, because the minerals give tap water a head start.
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