Batteries are made of two separate metals suspended in an acidic solution. Two suitable metals are copper and zinc. The lemon provides the acidity, a copper coin provides the copper and galvanized nails are coated in zinc. Insert the coin into one side of the lemon and the nail into the other side, ensuring the coin and nail do not touch. The nail and coin are now the electrodes of your battery. The coin is positive and the nail negative; the lemon juice is the electrolyte, or liquid that conducts electricity. Attaching a volt meter to the lemon battery will illustrate that the battery is working, though it will not provide enough power for a light bulb. Adding more lemon batteries and linking them together will produce more power, allowing for more impressive results.
This project illustrates how different fruits require different storage. Choose two different fruits, for example a banana and an apple, and gather three of each. Place each piece of fruit in a separate brown paper bag. Place one apple bag and one banana bag in the fridge, one of each in a basement or cold room and one of each in a warmer room. Encourage your child to hypothesize as to which area will keep the fruit fresh the longest and which will ruin it the quickest. Make a simple chart to allow your child to record the results every day. Allow three to four weeks for this project.
The slower a fruit dehydrates, the longer it stays fresh for eating. Gather several different types of fruit, such as banana, apple, pear and orange. Cut and weigh the fruits, ensuring each sample weighs the same. Place each sample on a paper plate, record the weight of each and encourage your child to hypothesize which fruit will stay freshest longest and which will dehydrate the fastest. Weigh the fruit every day for between one and two weeks, by which time all the fruit should be completely dried out.
In this project, a range of different fruits are tested for vitamin C content. First, make a vitamin C indicator solution. Mix a little water with 1 tbsp. of cornstarch to form a paste, add 8.5 fluid oz. of water and boil for five minutes. Add 10 drops of this solution to 2.5 fluid oz. of water and add enough iodine to produce a dark purple color. Place 1 tsp. of the solution into a small glass, one for each type of fruit being tested. Now add a few drops of juice from the fruit. The vitamin C causes the purple solution to lose its color, so the lighter the color, the higher the vitamin C content.