Have you ever wanted a rainbow wand
? Who hasn't, right? Here's an easy and colorful chemistry demonstration for you. Take a long glass tube and fill it with Universal Indicator solution. Add a few drops of 0.02M HCl to one end of the tube and seal it with a stopper. Add a couple of drops of 0.02M NaOH to the other end of the tube and seal it. The Universal Indicator will respond to the pH gradient by providing you with a lovely rainbow. You can invert the tube a few times to speed things up.
You can get a similar result using home chemistry. Fill a clear straw with red cabbage juice
. Add a little lemon juice or vinegar to one end of the straw. Add a few drops of baking soda or laundry detergent solution to the other end of the straw.
Another option is to set up a line of test tubes. Fill the tubes with liquids exhibiting a range of pH values and add universal indicator or cabbage juice to elicit a color change. Here's what you get with cabbage juice: