demonstrations:liquid_nitrogen_hot_water
Liquid Nitrogen in Hot Water
Materials: ★★★ Requires materials not commonly found in school laboratories
Difficulty: ★★☆ Can be done by science teachers
Safety: ★★★ Only to be attempted with adequate safety procedures and trained staff
Categories: Liquid Nitrogen
Alternative titles: Liquid Nitrogen Dense Fog
Summary
When liquid nitrogen is poured into a beaker of hot water, the nitrogen rapidly boils and chills the water vapor above it. This causes almost every evaporating water molecule to condense into tiny liquid droplets, producing a dense fog.
Procedure
- Heat water in a beaker until it is nearly boiling.
- Place the beaker on a heat-safe surface in a well-ventilated area.
- Using insulated gloves, carefully pour liquid nitrogen into the hot water.
- Observe as the nitrogen boils violently and a thick, white fog rapidly forms above the beaker.
- Point out that the fog is not actually nitrogen, but condensed water droplets created by cooling the escaping water vapor.
Links
Liquid Nitrogen and boiling water = FOG! - MrGrodskiChemistry:
Variations
- Try using different temperatures of water (warm, hot, boiling) to compare the amount of fog produced.
- Use a strong flashlight or laser pointer to highlight the fog and make the droplets more visible.
- Place the beaker inside a large glass tank to contain the fog and create a dramatic rolling-cloud effect.
Safety Precautions
- Safety glasses required.
- Wear cryogenic gloves when handling liquid nitrogen.
- Use heat-resistant gloves if moving hot glassware.
- Perform in a well-ventilated area to prevent oxygen displacement.
- Use only borosilicate (Pyrex-type) glassware to reduce the risk of shattering.
- Stand back after pouring to avoid splashes of hot water or liquid nitrogen.
Questions to Consider
- Why does hot water produce more fog than warm water when liquid nitrogen is added?
- What exactly is the white cloud we see, and why isn’t it nitrogen gas?
- Why does cooling water vapor make it visible when it is normally invisible?
- How is this similar to the way clouds form in the atmosphere?
- Could this principle explain why you can sometimes “see your breath” on a cold day?