Objective: Students will predict and observe the effects that freezing and thawing have on water as it floats and sinks in oil.
Key Concept: Water floats or sinks in oil depending on its state of matter.
freezer and ice cube tray
clear glass or plastic cup
1. Create concentrated color by setting a marker into a cup of water for a few minutes. Pour that colored water into an ice cube tray. Freeze until solid.
2. Ask students whether they think water is heavier or lighter than oil. Ask them to predict whether water will float to the top or sink to the bottom of a cup of oil. What will happen to water that is frozen solid versus thawed into a liquid? Ask the children to illustrate their predictions.
3. Nearly fill a clear cup with cooking oil. Place the colored ice cube into the cup. It will float to the surface. Ask students who predicted that to show their drawings.
4. Watch what happens as the ice cube melts. Observe the colored water sink to the bottom of the cup. Ask students who predicted that to show their drawings.
5. Discuss observations and what caused this to happen. When water freezes its molecules expand into rigid ice crystals that take up more space than when they were in a more compact form of matter (liquid). When they are less dense, they float above the heavier oil. As they melt and the molecules become more dense, they are heavier than the oil and sink.