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Anne Marie Helmenstine, Ph.D.

Make a pH Rainbow Wand

By February 17, 2014

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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:

Red Cabbage Juice pH Indicator (V. Belkhir)

Comments

October 22, 2010 at 12:04 pm
(1) Alan Crooks says:

I love the range of colours one gets with red cabbage indicator – my pupils also love making it and testing household chemicals with it.

The ‘rainbow in a tube’ would make a good display for parents’ evenings/open evenings etc :-)

October 25, 2010 at 1:09 pm
(2) zainab says:

nice 2 see them in the test tube bottels how brighter and kool it looks!!!!!!!!!!

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