EXPERIMENT: Mystery Powders Operating Guide Mystery ... - …

EXPERIMENT: Mystery Powders

Mystery Powders

Operating Guide

Visitors choose one of five unidentified powders. By performing various tests, they are able to identify whether their powder is baking soda, baking powder, citric acid, corn starch, or detergent.

OBJECTIVES:

Visitors learn that different chemicals can be identified by their chemical properties. Visitors learn to make inferences from observations.

SCIENCE TOPICS

Solubility Indicators Acids Bases Chemical Reactions

PROCESS SKILLS

Observing Investigating Inferring

VOCABULARY

Acid ? Base Universal Indicator Soluble

UNIT 7 CRIME SCENE CHEMISTRY EXPERIENCING CHEMISTRY ?2006 OMSI

U7.1

EXPERIMENT: Mystery Powders

Operating Guide

Mystery Powders

Procedure:

1. Always wear safety goggles.

2. Rinse the flask, spot plate, and scoop.

3. Choose one of the mystery powders. You are going to identify it.

4. Add one scoop of your powder to the flask.

5. Use the graduated cylinder to measure 20 ml of water and pour it into

the flask. Swirl vigorously for about 30 seconds.

4. Add 5 drops of indicator to the flask. Make observations as follows:

a) Are there suds or large bubbles? Is the solution purple?

If yes, then you have detergent! Start over with another powder.

b) Is the solution pink and clear?

If yes, then you have citric acid! Start over with another powder.

c) Is the solution pink and milky or cloudy?

If yes, then you have cream of tartar! Start over with another powder.

d) Still don't know which powder you have? Go on to step 5.

5. Put a scoop of the powder in each of 2 depressions in the spot plate. To the first, add 5 drops of vinegar. Stir with a toothpick. Do you see bubbles?

6. To the second depression, add 3 drops of iodine. What color is the iodine?

a) Is there bubbles? Is the iodine brown?

If yes, then you have baking soda! Start over with another powder.

b) Is there bubbles, but the iodine is black or purple?

If yes, then you have baking powder! Start over with another

powder.

c) Is there no bubbles, but the iodine is black or purple?

If yes, then you have starch! Start over with another powder.

7. Empty and rinse the flask and the spot plate.

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UNIT 7 CRIME SCENE CHEMISTRY EXPERIENCING CHEMISTRY ?2006 OMSI

How can we identify mysterious substances using chemistry?

A Closer Look:

Although each white mystery powder looks like the other powders, you were able to identify them by their very different chemical properties.

Detergent is the only mystery powder that will make suds.

Cream of tartar and citric acid are both acids, and they will turn universal indicator pink. Citric acid will completely dissolve in water, leaving a clear solution, but cream of tartar is less soluble and leaves a milky or cloudy solution.

Starch interacts with iodine and turns black-purple in a complex way scientists are still guessing about. Complicated iodide ions (I5-) probably stick inside starch molecules, changing their color.

Baking soda is a base that reacts with the acid vinegar to give off carbon dioxide gas. We see the gas bubbling from the solution.

?2006 OMSI

EXPERIMENT: Mystery Powders

Operating Guide

Baking powder contains baking soda and starch, as well as other ingredients. The baking soda bubbles in vinegar and the starch turns iodine black-purple.

Forensic scientists use similar techniques to identify suspicious unknowns found at crime scenes.

MATERIALS

(with amounts to have on hand) baking soda baking powder cream of tartar citric acid corn starch detergent water vinegar (household) universal indicator iodine solution 125 mL flask 25mL graduated cylinder 1 large squeeze bottle 2 small squeeze bottles 6 containers with screw-top lids 6 microspatulas Two 200mL beakers spot plate toothpicks small plastic beaker for used toothpicks small bottle with nozzle to dispense toothpicks

Setup/Takedown Procedures

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UNIT 7 CRIME SCENE CHEMISTRY EXPERIENCING CHEMISTRY ?2006 OMSI

ORIGINAL SETUP

Label the six containers with screw-top lids as: "Mystery Powder A", "Mystery Powder B", "Mystery Powder C", "Mystery Powder X", "Mystery Powder Y", and "Mystery Powder Z."

Label the stock containers of powders as follows: "A cream of tartar" (red label), "B detergent" (yellow label), "C baking soda" (yellow label), "X citric acid" (red label), "Y baking powder" (yellow label), and "Z starch" (white label).

Fill the six containers with the appropriate white powder according to the key given above.

Label the six micro-spatulas as: "A", "B", "C", "X", "Y", and "Z". Fill the large squeeze bottle with water, and label it "water" (blue label). Fill one small squeeze bottle with universal indicator and label it

"universal indicator" (purple label) Fill one small squeeze bottle with iodine solution and label it "iodine

solution" (orange label). Label small bottle with nozzle "toothpicks" (white label). Label the spot plate "spot plate" (white label). Label small plastic beaker "used toothpicks" (white label).

WEEKLY SETUP

Check powder levels in all containers and replenish stocks. Retrieve universal indicator bottle from flammables storage.

DAILY SETUP

Set out the visitor instructions in a Plexiglas holder. Refill mystery powder containers with appropriate powders. Refill Universal Indicator and vinegar bottles. On a tray lined with a white mat, set out the following:

o Mystery powder containers A, B, C, X, Y, and Z with the appropriately labeled micro-spatulas

o Spot plate o Flask o Universal Indicator squeeze bottle

?2006 OMSI

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