A lemon can produce electricity -- just like a battery cell. To make a lemon battery, start with one lemon, a galvanized steel nail and a penny. Make two one-inch cuts on the lemon. Insert the nail in one cut and the penny in the other. This creates a single-cell battery because the nail and penny become electrodes in the lemon, now an electrolyte. See Resources for information on how to create a double-cell battery (or even larger) to power light bulbs, digital clocks or any low-voltage items.
Create a secret message using lemon juice. Dip a cotton swab or paintbrush into a bowl of lemon juice. Write your message on a piece of paper using the swab or brush. Make the message appear by either applying heat to the paper after it dries or rubbing salt on it while still wet, wiping off the salt and then going over the message with a crayon. This project works because lemon juice is acidic, which weakens the paper, allowing the message to be embedded in the paper.
This project results in a chemical reaction. To start, stretch a balloon to make it more inflatable. Pour about two ounces of water into a soft drink bottle. Drop in a teaspoon of baking soda and stir it around with a drinking straw. Pour in the juice from one lemon, then quickly stretch the mouth of the balloon over the opening of the soft drink bottle. The lemon juice combined with the baking soda creates carbon dioxide, a gas that will form in the bottle until it inflates the balloon.
This bubbly project begins with a teaspoon of baking soda in a glass. Drop in a dollop of dishwashing liquid. Add a few drops of food coloring (optional). Squeeze a lemon into the glass and stir. As you do, bubbles will form and start to overflow the glass. For even more fizz and bubbles, drop in additional baking soda and lemon juice. As with the balloon inflation above, the baking soda reacts with the lemon juice to create carbon dioxide, although this time that gas is trapped by the soapy liquid to create the fizz. Warning: don't drink this mixture -- but you can wash dishes with it!