The Mysterious Sunken Ice Cube
Concept: Density The science concept in this experiment is density. An ice cube in water will float, while the ice cube placed in ethyl alcohol will sink because it is more dense than the alcohol.
Pre-demo preparations: make ice cubes with food coloring before
two 400 mL beakers
250 mL graduated cylinder
ice cubes (with food coloring)
300 mL water
300 mL ethyl alcohol
150 mL Mazola corn oil
1. Fill one beaker with 300 mL of ethyl alcohol.
2. Fill one beaker with 300 mL of water.
3. Put the 150 mL of corn oil into the graduate cylinder.
3. Drop ice cubes in each beaker and the graduated cylinder.
Introduction: OK.... how many of you ever threw a rock into a lake before, what happens to the rock? It sinks, right? How many of you like water or pop with ice in it? What does the ice do in the liquid you are drinking? It floats, right? Here, I have three liquids, both clear and odorless, one which is yellow. Next I am adding ice cubes with food color in them.
Explanation: That was neat huh? Does anybody have any ideas why in one beaker the ice cubes sunk and the in the other one they floated? Well one beaker is filled with water, the other beaker has a substance called ethyl alcohol. An object that is less dense than the liquid it is in will float on top of the liquid. An object that is more dense than the liquid it is in will sink to the bottom. The ice cube is less dense then the water so it will float on the top. The ice cube is more dense then the ethyl alcohol so it will sink to the bottom.
Now what has happened to the ice cube in the corn oil? Initially the ice is floating on top of the oil, therefore it must be less dense than the oil. But look what is happening as the ice melts, the water seems to be dropping to the bottom because the liquid water is more dense than the oil.
Be careful handling glassware.
Make sure students are informed that even though ice and water are OK to drink, you should never consume ethyl alcohol or really anything in an experiment.
Rinse out both beakers in the sink.
Thoroughly clean out all glassware with soap and water.
If there is remaining ice, it can be allowed to melt in the sink.
1. Summerlin, L, Ealy, J, Chemical Demonstrations, Vol. 2, American Chemical Society, 1987, p. 16.
2. Bridges, B, CHEM 13 NEWS, April 2002, p. 8.