Acid/Base Chemistry: The Cabbage Caper

Still have some red cabbage juice indicator in the freezer?  Pull it out for this fantastic investigative lesson, utilizing knowledge of acid/base indicators. 

The story begins....

Click here for the full story, with all the suspect information. 

When you've read the full story, you'll learn that each of the suspects was using a particular solution.  The students test each of those solutions with red cabbage juice and with turmeric (found in the spice section of the grocery store) to determine which solution, and therefore which suspect, was responsible for the green and orange stains and the murder of Mr. Worthington. 

The suspects' solutions:

• Water
• Salt Water
• Battery Acid (you can use any kind of weak acid)
• Lemon Juice
• Vinegar
• Lye (baking soda dissolved in water will serve the purposes of the lab)
• Ammonia Water (you could use window cleaner)

If you have spot plates, students could set up their tests in one of those - put each suspect's solution in two wells, then add a few drops of cabbage juice to one of those wells and a few grains of turmeric to the other.  If not, use test tubes or small beakers, just make sure to wash them well between each test (you wouldn't want an innocent person to be accused of murder!). 

To conclude the lab, have students summarize the tests they performed and the results of their tests in a statement for the court.

One more note, the color change in turmeric is subtle - it remains yellow in an acid but turns orange in a base.

Today, homicide division has asked you, a reputable chemist, to personally accompany Detectives Sippowicz and Martinex on a murder case. Mr. Robert Worthington, a prominent citizen of our fine community, has been murdered.

On the way to the Worthington mansion, you learn that Mr. Worthington was stabbed, in his own kitchen, with his own carving knife. The maid, according to the police report, had found the cook standing over the body. The police officer on the scene had, therefore, arrested the cook on suspicion of murder. The cook, being a good friend of Sippowicz, had immediately called him, seeking his help. Sippowicz claims that the cook could not have done it since Mr. Worthington paid his cook more than any other employer in the city. His death will mean a substantial reduction in the cook’s salary, he claims. Besides, she is a very gentle person. She would never even raise a hand to kill a fly.

When you arrive on the scene, Mr. Worthington is still lying on the kitchen floor with the carving knife still protruding from his chest. As you examine the knife, you notice a STRANGE GREEN STAIN on the handle. Nearby are some ODD ORANGE STAINS. These are unusual because they are not blood stains. Fingerprints are covered up by the stains, making them unavailable for evidence. As Martinez questions the cook, you and Sippowicz set out to question the rest of the staff. One hour later, you, Martinez and Sippowicz meet to discuss the suspects.