Cookie CheMYSTERY chemical analysis lab

The local bakery needs your help! They lost the secret recipe for Grandma’s Amazing Sugar Cookies, and are down to their last bag of mix. For this lab, use careful observation to determine the ingredients included in the mix.

New on my Teachers Pay Teachers store! This lab started as the lead-in to a holiday break, but it could be done any time. Students practice chemical analysis techniques using common substances from the grocery store in small-scale reactions and tests.

A fun physical science lab

There are six known substances:

• Flour
• Cornstarch
• Powdered Sugar
• Baking Soda
• Baking Powder
• Citric Acid

Students test each with six tests:

• Smell
• Touch
• Water
• Vinegar
• Iodine
• Heat
• (Optional for homeschoolers: Taste)

Once data is collected on all six known substances, students repeat the tests on the Unknown in order to determine which of the known substances are mixed together.

Food Chemistry

There’s a lot of chatter lately about chemicals in food, etc…, and it seems like many people are just not sure what “counts” as a chemical. This lab helps students see that regular ingredients found in a cookie recipe can have some interesting chemical properties (and have chemical formulas and chemical names!)

A few interesting ones:

1. Baking Soda is sodium bicarbonate (NaHCO3). It is basic when dissolved in water. When combined with an acid like vinegar, the reaction releases carbon dioxide gas. Most kids know this.
2. Baking powder is a mixture of baking soda and two different powdered acids. One of the acids (monocalcium phosphate) reacts with the sodium bicarbonate as soon as both ingredients are wet, and produces carbon dioxide. The second acid (sodium acid pyrophosphate or sodium aluminum sulfate) reacts with sodium bicarbonate only at higher temperatures. This extends the leavening process and is preferable for some baked goods. Because baking powder contains both an acid and baking soda, it will fizz when water is added. (Two acids: “Double-Acting” baking powder!)
3. Citric Acid (C6H8O7) was a new discovery for me. This can be found in a couple of parts of the grocery store — I found it with the canning supplies. It’s granular and resembles granulated sugar in texture. In foods, it can be found as a flavoring or preservative, and some people add it to already-prepared foods as “sour salt.” It is VERY acidic when dissolved in water (dramatic for this lab!) If you mix baking soda and citric acid, you get something that behaves like baking powder – fizzing when water is added.

I have another project to write up soon that invites students to research the chemicals in processed foods – their origins, processing, and other uses. What kids find from this is that almost all of the chemical-sounding ingredients in their food are made from corn or soy, and most have a multitude of non-food (and sometimes very unappetizing) uses. Check out Twinkie, Deconstructed by Steve Ettlinger.

Try This at Home

I also added pH to the list of tests in this lab. With that and the Citric Acid addition, I needed to try the experiment at home. pH paper isn’t easy to obtain locally, so I ordered some. I dissolved each of the six known substances (and my preferred unknown mixture) in water, and checked the pH of the result. It was beautiful!

• Flour, cornstarch, and sugar were neutral. (Our tap water is slightly acidic.)
• Baking soda was basic.
• Baking powder was neutral (once the reaction finished). I looked back later and the paper had turned green after a few minutes. Not sure why.
• Citric acid was acidic!
• The unknown mixture was basic (because it contains baking soda but no acids). Good. That means pH can be used as a diagnostic test for this unknown.
• I also tried mixing baking soda and citric acid, and then adding water. Lots of fizzing resulted! pH testing showed that there was excess acid in the mixture I made.

pH paper is fun to experiment with. Kids should try it, even if they have no understanding of chemistry at all. Notice the small sample sizes in the picture! You don’t need much of any of the substances to do this lab.

Download Cookie CheMYSTERY here!

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