Happy Birthday Rosalind Elsie Franklin

Rosalind Elsie Franklin, born July 25, 1920, was a Physical chemist and crystallographer who worked on the X-ray diffraction images of DNA which formed a basis of Watson and Crick's hypothesis of the double helical structure of DNA in their 1953 publication.  When published in its own article along side Watson and Crick’s, her data constituted critical evidence of their hypothesis.  Later, she led pioneering work on the tobacco mosaic and polio viruses.

Test Tube Science: Black Bean Indicator

There are lots of acid/base indicators available in the home.  The one I'm going to talk about today is an indicator made from black beans.

Marcelle was making a big batch of feijoada and started the black beans soaking the night before we were going to have it for dinner.  As she was preparing to pour off the blue/purple water they had soaked in I asked her to save some for me.

The dinner was delicious. And I decided that I'd see what colors I could come up with after dinner.  In the picture below you can see the spectrum of colors obtained from my black bean juice with vinegar and baking soda.

Black bean indicator: acidic on the left, neutral in the middle and basic on the right.

To make your own indicator take 10-15 dry black beans put them in a test tube and cover them with water.  Let them soak for 10-12 hours for the most concentrated solution.  Now you can remove the water and use it as an indicator in other solutions.  Dilute the black bean juice 1 part juice to 4 parts test solution.

If you want to get some indicator in 10 minutes instead of 10 hours you can soak the beans in 70% isopropyl alcohol.  The alcohol will make a solution much faster.

Acid, neutral, and basic forms of anthocyanins.

The primary color changing molecules in black beans are anthocyanins. As the pH of the solution changes the structure of the molecule changes.  This changes its absorption spectrum thus changing the color of the solution. These reactions are in equilibrium making them great natural indicators.

U and I Together

Man: If I were designing the periodic table I'd put U and I together.
Woman: A then both Mendeleev and I would cry.