Water at rest will naturally create a "film" of surface tension where it comes into contact with air. However, the chemical properties of liquid dish soap will bond it with the water molecules to break that tension. One way to demonstrate this is to gently place a paper clip on the surface of a pan of water so that it floats. A small piece of paper towel might make this easier. When dish soap is added, the paper clip will sink. You can also sprinkle pepper on the surface and watch it scatter as the surface tension breaks.
Fold a paper towel over a few times and soak the towel in vinegar. Then place a shiny penny on the towel and let it sit for at least a day. Eventually, it will turn green. This happens because the vinegar's chemical properties affect the penny, causing it to react with the oxygen. The copper in the penny begins to oxidize, creating a green coating called copper oxide.
Pour 1 tablespoon of yeast and 1 teaspoon of sugar into a balloon with a funnel. Fill the balloon with warm water without stretching it and tie it off. Let the balloon sit in a warm place. Soon, it will start to expand dramatically. The sugar and warmth trigger the yeast -- which is alive -- to grow. As the yeast expands, it releases a chemical called carbon dioxide in the form of a gas, which causes the balloon to expand.
You can use the juice of red cabbage to test whether a liquid is an acid or base. Grate a head of red cabbage and soak the cabbage in cold water for 45 minutes and strain it to extract the juice. Pour a cup of the juice and mix in 1 teaspoon of baking soda. The baking soda is a base that will counteract the acidic properties and turn the juice blue. Now, add in an acid-like lemon juice and watch the color go back to reddish-purple.