Coaching Mystery Powders: One Teacher’s Approach

After going over the rules with the team members, I use one of two training approaches which require the students to build their own understandings rather than tell them what to look for:

Introduce:
The tests: touch, flame, iodine, vinegar, red litmus paper(reacts with bases), blue litmus paper (reacts with acids)
The powders: powdered sugar, baking soda, flour, salt, cornstarch, plaster of Paris, citric acid

1. Somewhat Quicker Procedure
If I don’t have a lot of time, I model the process of applying each test to every powder.  The team members are supplied with pencils and paper in order to record observations.  I ask them to think about what they see, feel, and smell and write sort of a short journal-type reaction to each test.  We also talk about the chemistry that makes each thing happen.  When every test has been demonstrated for each powder, I send the groups to discuss and develop their own chart or graphic organizer that will help them find the information quickly.  A blank could be prepared for them to fill in from their notes if necessary, but I find more ownership and success when they create their own.  

2. Longer Procedure
I talk the students through every test, telling them what to do and asking them to think about their observations before recording their notes.  The students experience each test themselves, then take their notes and create their chart.

The students are encouraged to use very descriptive words in their chart to help differentiate between similar reactions.  After the students have created a chart to organize their observations, I ask them questions about each test and how to distinguish between two that acted the same way, for example:
 Which powders reacted to iodine? What other test could you use to tell which one is which?
 Are there any powders that you can find with only one test?

Then, the students are instructed to make a plan of attack…which test will we do first? Second?  Which powders will we try to eliminate right away?  This can be written on their chart as well.  Time is the tie-breaker, so an efficient plan of attack helps a lot.  

In practice sessions, the students start by telling each other exactly how many in each mixture using only the 7.  Then, only 6 or 5 will be used.  Then, some of them can be repeated or one can be sitting alone to increase the difficulty.  The students make up mixtures at home and trade them to be tested later and check each other’s success.

 I find it more successful to let the students make the mistakes and learn from them rather than tell them what to do and what to look for.



In your study packet, Mixture A has 3 powders, Mixture B has 2 powders, and Mixture C has 3 powders.  Count it up and it equals 8.  There are only 7 possible powders, so one must be repeated.

***Drug Mart usually carries food-grade citric acid with its canning supplies.  I’ve been lucky to find it there often.