Sinking Ice Cube

Materials: ★★☆ Available in most school laboratories or specialist stores
Difficulty: ★☆☆ Can be easily done by most teenagers
Safety: ★★☆ Some safety precautions required to perform safely

Categories: Density and Buoyancy

Alternative titles: Ice and Density

Summary

Two beakers contain clear, colorless liquids - water and ethyl alcohol. An ice cube floats in the water but sinks in the alcohol because of the lower density of ethanol.

Procedure

Fill one beaker with ~100 mL of water and another with ~100 mL of ethyl alcohol.
Show students two similar-sized ice cubes.
Place one ice cube into each beaker.
Observe: the ice cube floats in water but sinks in alcohol.
Ask students to propose hypotheses explaining why the outcomes differ.

Links

Density - Ice in Alcohol & Water - Bond with James:

📄 Case of the Sunken Ice Cube - Flinn Scientific: https://www.flinnsci.com/api/library/Download/b5fd3e87e1b148e1a8eaf73296fb9d2f?srsltid=AfmBOop33Q9uNtq5gDs5tpRPz_Y64pRN6yLY0JwncSz1AuUw3SyfP1sx

Variations

Mix water and alcohol in varying ratios to find the composition where the ice cube is suspended in the middle.
Have students calculate the density of both liquids by measuring mass and volume.
Compare with other liquids (oil, salt water, corn syrup).
Discuss why ice floats in water, even though most solids are denser than their liquids.
Explore seawater vs. freshwater densities (1.03 g/cm³ vs. 1.00 g/cm³) and buoyancy in lakes vs. oceans.

Safety Precautions

Ethyl alcohol is flammable—keep away from flames and sparks.
Wear chemical splash goggles and an apron.
Handle glassware carefully to avoid spills and breakage.
Dispose of liquids according to local regulations.

Questions to Consider

Why does ice float in water but sink in alcohol?
What role does density play in determining whether something floats or sinks?
How does hydrogen bonding explain the unusual behavior of water when it freezes?
Is it easier to float in freshwater or seawater, and why?