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WhoDunIt?


Help! Grandma Ruffman's been arrested! Detectives say she baked a cake with a metal file in it so that my notorious brother Scruff Ruffman could use it to break out of jail! But sweet old Grandma would never turn to a life of crime! The cake in question was made with baking soda. Quick! Head to the crime lab to test the powder found on Grandma Ruffman's apron. If it's something besides baking soda, she's innocent!

Today's challenge is to solve the case of the mystery powder-the secret is in the science!

  • Target Age: 8-10
  • Skills/Subjects: Science
  • Related Episode: Episode 317: The People vs. Grandma Ruffman

WHAT TO DO

1. Get what you need:

  • Data table
  • Pencil
  • Purple grape juice
  • White vinegar
  • Iodine
  • 3 cups, each with 1 teaspoon of baking powder
  • 3 cups, each with 1 teaspoon of flour
  • 3 cups, each with 1 teaspoon of baking soda
  • 3 cups, each with 1 teaspoon of the mystery substance
  • 3 pipettes or eyedroppers
  • Paper towels
  • Sticky notes (to use as labels)

labeled cups in a grid

2. Set up your work station:
Make labels for the powders and liquids listed below and arrange in a grid on a table. Get 3 cups containing each powder (9 in total), and line them up under their labels (see illustration). Your cups with the mystery substance come later!

 

 

 

 

 

a table for data

3. Test, observe, and record:
Put 5 to 10 drops of grape juice in one cup of baking powder. What happens? Record your observations on the data table. Now try the grape juice on the other two powders, recording your observations each time.

In some cases, a chemical reaction will occur. Signs of a chemical reaction include foaming, fizzing, or a change in color. But sometimes no chemical reaction can be seen. Can you tell the difference?

4. Repeat step 3:
Test all the liquids with all the powders and write your observations on the data table. Use a new pipette with each liquid.

5. Test the mystery substance:
Get 3 cups containing the mystery substance and line them up next to the grape juice, vinegar, and iodine. Test and record your observations. (Hint: the mystery powder is one of the three powders you already tested!)

6. Compare data and draw conclusions:
Did your observations about the mystery substance match any of the three powders you tested? By comparing your data, can you figure out what the mystery substance is? Explain your reasons. Did you prove Grandma Ruffman's innocence? Remember: The cake at the crime scene was made with baking soda. Does the mystery substance found on Grandma's apron match it, or is it different?

CHEW ON THIS!

In this activity, you performed an experiment and analyzed data like a scientist does. A chemical will react in the same way every time, as long as the conditions are the same. You set up the experiment so that each powder was tested in exactly the same way. Then you observed the chemical reactions closely and recorded your data. When you drew conclusions about what the mystery substance was, your conclusions were supported by scientific evidence.

The Mystery Substance

If you're doing this activity at home rather than in a group setting with a leader, you'll need a parent or someone else to set up the mystery substance for you. Have the person pick one of the three powders you're testing (baking soda, baking powder, or flour), and add a teaspoon each to 3 cups. The person should keep the identity of the powder a secret-after all, this is a mystery you're supposed to figure out! When you've finished testing, tell the person what you think the mystery powder is-were you right?

Download a printable version of this activity:

*Adobe Reader required for PDFs

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