EXPERIMENT: Mystery Powders
Operating Guide
Mystery Powders
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
PROCESS SKILLS
VOCABULARY
Solubility
Observing
Acid – Base
Indicators
Investigating
Universal Indicator
Acids
Inferring
Soluble
Bases
Chemical Reactions
UNIT 7 CRIME SCENE CHEMISTRY
EXPERIENCING CHEMISTRY ©2006 OMSI
U7.1
EXPERIMENT: Mystery Powders
Operating Guide
Mystery Powders
Procedure:
1.
2.
3.
4.
5.
Always wear safety goggles.
Rinse the flask, spot plate, and scoop.
Choose one of the mystery powders. You are going to identify it.
Add one scoop of your powder to the flask.
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.
U7.2
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
U7.4
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
EXPERIMENT: Mystery Powders
Operating Guide
o
Vinegar squeeze bottle
o
Toothpicks in small bottle
o
Graduated cylinder
o
Small beaker for used toothpicks
DAILY TAKEDOWN

Discard used toothpicks.

Wash the outsides of bottles, spot plate, flask, graduated cylinder,
mat, and counter top.

Replace the caps on all bottles and move all chemicals under the
sink.
WEEKLY TAKEDOWN

Replace bottles on powders and return to tub.

Return universal indicator stock bottle to flammables storage.

Clean the tray and leave it at the station.
RUNNING SUGGESTIONS

Encourage visitors to try identifying other powders after their first.

Do not fill powder containers full, as they may spill and/or become
contaminated by liquids.
EXTENSIONS

U7.6
Encourage visitors to predict how the powders will react with each
other, based on how they reacted with the test solutions. Baking
soda turns indicator blue. But baking soda also reacts with vinegar
to produce bubbles. We guess that baking soda is different from
vinegar. If that is so, is vinegar likely to turn the indicator blue (like
baking soda) or pink (unlike baking soda)? Try it!
UNIT 7 CRIME SCENE CHEMISTRY
EXPERIENCING CHEMISTRY ©2006 OMSI
Safety & Disposal
Health: 1
Flammability: 0
Reactivity: 0
Contact: 0
Health: 2
Flammability: 1
Reactivity: 1
Contact: 1
Caution: Povidone Iodine Solution 10% is poisonous by ingestion
and can be hazardous to the skin, causing stains. Wear goggles
and gloves when using, and wash hands afterwards. See MSDS for
further information.
Caution: Universal Indicator solution contains denatured alcohol
which is highly flammable and moderately toxic by ingestion and
inhalation. See MSDS for further information.
No special precautions are required for other chemicals. Follow
standard lab procedures.
Disposal: All unused solutions may be poured down sink drain.
Follow standard lab procedures.
MATERIALS PREP
Vinegar, universal indicator solution, and all food powders may be used as purchased.
©2006 OMSI