Supercooling Water!
Key Concepts
Materials:
1 bottle distilled water
1 large container (try to find a container that’s deeper than the water bottle is tall)
4 tbsp salt
Ice cubes
Activity Directions:
Discussion Questions & Science Explanations:
Additional Experimentation:
- Fill your large container with ice.
- Sprinkle some salt onto the ice.
- Place your bottle of water into the container of ice. Be sure to surround it as much as possible with ice cubes.
- Set a timer for 10 minutes. Be careful not to disturb the water!
- After 10 minutes have passed, carefully remove the bottle of water out of the container.
- If the water has already frozen, this activity will not work. Please try again with another bottle of liquid water, and add additional ice cubes if all of the ice has already melted.
- Note that despite being immersed in the ice, the water inside of the bottle is still liquid.
- Strike the bottle against a table quickly.
- Watch how the water in the bottle quickly transforms into ice!
Discussion Questions & Science Explanations:
- How do particles in a solid behave, in terms of their movement and spacing? How about liquids and gases?
- Particles in a solid are barely moving, just vibrating, and are pretty close together.
- Particles in a liquid are farther apart and move faster than particles in a solid, and gas particles are even more spread out and move even faster than particles in a liquid or solid.
- Gas particles have the most energy, followed by liquid particles which have less energy, followed by solid particles which have even less energy.
- Where did the heat travel in this activity?
- Heat travels from hot objects to cold objects. A helpful tip to figure out where heat is traveling is to think out which object is hotter and which object is colder. In this situation, the hot object is the bottle of water and the cold object is the ice. The heat moved from the ice into the bottled water and this reduced the temperature of the water in the bottle.
- Was this a chemical reaction? And if so, why?
- A chemical reaction occurs when the molecular bonds of a substance change.
- Changing the physical properties of a substance, such as state of matter, isn’t a chemical reaction because the substance is still the same. Some common examples of each include: burning wood (chemical), cooking an egg (chemical), iron rusting (chemical), ice melting (physical), cutting paper(physical), mixing play-doh (physical).
- Transforming water into ice is not a chemical reaction, it’s actually physical. The liquid water simply decreases in temperature and becomes solid ice.
- Have you ever seen somebody sprinkle salt on the road on an icy winter day? Do you know why they do that?
- Salt lowers the melting point of the ice.
- Water freezes at 32 degrees Fahrenheit but saltwater freezes at 28.4 degrees Fahrenheit.
- This means that at about 30 degrees Fahrenheit, pure water will be ice, but saltwater will be liquid, even though both are the same temperature. The liquid saltwater can move around the bottle more easily, and therefore cover more area of the bottle. This allows for a more efficient transfer of heat, which lowers the temperature of the water faster.
- Why did we have to slam the bottle down onto the table?
- Liquid water can actually stay liquid below its freezing point, 32 degrees Fahrenheit.
- In this state, it’s known as supercooled water.
- Since all of the water in the bottle is still, it’s hard for the water molecules to form the crystal lattice structure that’s found in ice. However, jolting the water gets the water molecules moving around so that they are more likely to form that crystal lattice. Once the first crystal is formed, the rest of the water molecules join in, and all of the water in the bottle forms ice!
Additional Experimentation:
- Try supercooling different types of liquids like soda—can you get the same effect?
- See how light of a tap can set off the chain reaction that freezes the bottle of the water.
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Published 9.12.2020
Author: Alex Zhang
