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Crime Lab – Case of Chez Yum-Yum
Safety:
You are working with sharp objects and glassware. You are working with poisonous substances.
Caution: Iodine is corrosive and poisonous. It can stain skin and clothing. Rinse any iodine spills with water.
Procedure:
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Using a wax marking pencil, label 12 compartments on your tray. Label 3 of them “C” for Cornstarch. Label 3 of
them “P” for baking powder. Label 3 of them “M” for substance found at home of Meany-pants. Label 3 of
them “H” for substance found at home of Herbert.
Place a small amount of cornstarch in the compartments labeled “ C”. In your data table, write a description of
the cornstarch. Remember to be specific.
Place a small amount of baking powder in the compartments labeled “P”. In your data table, write a description
of the baking powder. Remember to be specific.
Place a small amount of substance “M” in the compartments labeled “M”. In your data table, write a description
of the substance. Remember to be specific.
Place a small amount of substance “H” in the compartments labeled “H”. In your data table, write a description
of the substance. Remember to be specific.
Predicting. Look at the four substances in your compartments. Compare the known substances “P” and “C” to
the unknown substances “M” and “H”. Based on your observations, predict whether testing will show that the
samples found at the suspects houses will match those spilled in the bakery. Record your prediction Here:
7. In one of your compartments for each substance, place 3 drops of water. Mix the two substances a bit with a
clean toothpick. In your data table, write a description of the result. Remember to be specific.
8. In one of your compartments for each substance, place 3 drops of iodine. Mix the two substances a bit with a
clean toothpick. In your data table, write a description of the result. Remember to be specific.
9. In one of your compartments for each substance, place 3 drops of vinegar. Mix the two substances a bit with a
clean toothpick. In your data table, write a description of the result. Remember to be specific.
10. Rinse all materials out of your compartmentalized trays and flush them down the drain with at least 10 times as
much water. Return trays clean trays to your lab station. Dispose of toothpicks in the trash. Wash your hands
thoroughly with soap and water.
Analyze and Conclude:
1. Were you able to use the ability to dissolve in water to distinguish all 4 materials? Explain?
2. Which of the interactions produced a chemical change? What happened to signify that a chemical change
might have taken place?
3. Are the samples from either of the suspects consistent with the substances spilled at Chez Yum-Yum? What
makes you think a given suspect may be guilty of the crime? Be specific!