Boiling Water Experiment 

Experiment

Have an adult help you with the following:

1. Fill a pot with water and place a tight lid on it.
2. With the lid on, heat the water to boiling.
3. Let water boil for 3 minutes.
4. Turn off heat.
5. Wearing an oven mitt, carefully lift the lid off the pot and observe the phase changes of water.

Download Instructions

What do you notice about the underside of the lid? When you placed the lid on top of the pot at the start of the experiment, the lid was dry. Now it has drops of water covering it. If you were to tilt the lid gently from side to side, you would notice that the droplets start to collect. Where is that water coming from?

When you filled the pot with tap water, the water was clearly in its liquid state. As you heated up the water on the stove top, the heat gave the water molecules energy. So much energy in fact, that they start to break apart and evaporate into the air as a gas. You can see evidence that the water was a gas because you can see steam. Steam is actually condensed molecules of gas as they cool quickly after being released from the surface of the liquid water. Also, when the heated water vapor hits the underside of the lid, the water molecules begin to cool down and join together again, making the water droplets that you observed underneath the lid.

This experiment is an example of water changing phases in a way that's similar to the water cycle. We observed water changing from a liquid (tap water) to a gas (steam) and back to a liquid (condensed water under the lid) that then falls back down to the pot of water after cooling.

Let's take a moment and further connect this experiment with the water cycle. Please match the step in the water cycle on the left with the similar step in the boiling water experiment.