Make invisible ink by mixing equal parts baking soda with water. Dip a cotton swab into the mixture, and use the tip to write a message on a piece of blank paper; set the paper aside to dry. Make the ink reappear by introducing a heat source, such as a lighted incandescent light bulb. As the baking soda mixture heats up, it will turn a pale brown and become readable.
When teaching about the concept of acids and bases, allow students to test household items for their acidity levels. For this experiment you'll need several pH strips, as well as foods, beverages, and various household cleaners. Have students write down the list of collected sample items, and hypothesize the substances' acidity. Test the product by submersing the pH strip in the liquid, or swabbing the strip with the liquid and write down the actual pH level; compare the hypothesis with the actual results.
Observe how yeast works by emptying a packet of years into a bowl of warm water and one teaspoon of sugar. Stir the yeast and water mixture together and let sit for about 10 minutes. You should see a bowl full of bubbling yeast. As the yeast feeds upon the sugar it produces carbon dioxide, which you see as bubbles.