Mystery Powder Analysis

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posted:: 10/4/2012
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Gizmo Exploration Guide
CSI Atlanta: Mystery Powder Analysis
The science of fighting crime has evolved tremendously over the past hundred years.
While the image of the diligent inspector peering through his magnifying glass is
common in literature and the movies, today's crime-fighters usually work in very
sophisticated laboratories.

One of the most common activities undertaken in these labs is the analysis of an
unknown substance to determine what it's made of.

Analysis of Known Substances

In this activity, you will conduct five standard tests on five known substances.

1. In the Gizmo™, make sure that Known is selected under Select a
sample. Then drag the tube labeled BAKING POWDER to the empty
stand. Under Appearance, click Test.
a. Examine the substance. Does it appear to be a smooth powder or
does it contain distinct crystals or chunks? (1) Create a table like
the one shown here and record your observations as you perform
each test on the known substances. (2)

b. Under Litmus test, click Test to dip a piece of red litmus paper
and a piece of blue litmus paper into a solution of the baking
powder. Litmus paper is used to determine whether a solution is an
acid or a base. If both pieces of litmus paper end up blue, the
solution is a base. If both pieces of litmus paper end up red, the
solution is an acid. If neither paper changes color, the solution is
neutral. Is the baking powder solution an acid, a base or is it
neutral? Enter your conclusion into your data table. (3)
c. Under Vinegar test, click Test to add vinegar to a solution of the
baking powder. Some substances bubble when exposed to vinegar.
Some do not. Does the baking soda solution bubble when exposed
to vinegar? Record your observations in your table. (4)
d. Under Biuret test, click Test. A Biuret test detects protein in a
substance. If the substance contains protein, the blue Biuret
reagent (substance used to detect another substance) will turn
purple. Does the baking powder turn purple when the Biuret
reagent is added? Record your observation in your table. (5) Does
baking powder contain protein? (6)
e. Under Iodine test, click Test. Iodine is used to indicate the
presence of starch and turns solutions that contain starch a dark
gray or black. Does the baking powder contain starch? (7)
2. Click Reset. Move one of the other tubes containing a known substance to
the testing stand. Conduct each of the five tests on that substance and
carefully record your observations in your table. Repeat the process with
the remaining "knowns" to create a table containing the test results for all
five substances. (8) Here is a selection of questions from your findings:
a. Describe the appearance of salt. Is it a smooth powder or is it
crystalline? (9) Compare the appearance of gelatin with that of
baking powder. (10)
b. Is the baking soda solution an acid or is it a base? (11) What about
the gelatin solution? (12)
c. Describe what happens when vinegar is added to the baking soda
solution. (13) What other substance(s) had the same reaction? (14)
d. What occurred when the Biuret reagent was added to the gelatin
solution? (15) What does this indicate about gelatin? (16)
e. What was the reaction when iodine was added to corn starch? (17)
Does corn starch contain starch? (18) Are you surprised by this
result?
Analysis of Unknown Substances

In this activity, you will conduct the same five tests that you used in the previous
activity on a series of unknown substances, and attempt to identify them. You will
refer to the table that you completed in the previous activityto help in this
identification.

1. Click Reset. Under Select a sample, check Unknown. DO NOT click on
New sample before completing this activity. If you HAVE clicked on New
sample at any point, click Refresh in the browser window to restart the
Gizmo.
a. Drag tube 1 to the empty test tube stand. Conduct each of the five
tests on the substance in tube 1. Record your findings in a table
similar to the one that you used in the previous activity. (19) Do
the results of the tests exactly match the results for one of the
known substances? (20) What substance is in tube 1? (21)
b. Return tube 1 to its original position either by dragging it or by
clicking Reset. Drag tube 2 to the empty test tube stand. Repeat
the five tests with the substance in tube 2 and record your data in
your table. What is the substance in tube 2? (22)
c. Repeat the process with tubes 3, 4, and 5. What substance is
contained in each of these tubes? (23, 24, 25)

2. Click Reset. You will now test the substances in the second row (tubes 6
through 10). Note that these tubes contain a mixture of TWO known
substances. Again, if you have clicked New sample at any point, then
click Refresh in your browser to restart the Gizmo.
a. With Unknown selected, drag tube 6 to the empty test tube stand.
Conduct each of the five tests on the substance in tube 6 and
record your data in a table. (26) Do the test results that you found
exactly match any one of the known substances? Why or why not?
(27) Because tubes 6 through 10 contain mixtures, your test
results will reflect a combination of the characteristics of the
individual substances.

•Acid test — If an acid or a base is mixed with a neutral substance, the litmus
test will indicate an acid or a base respectively.

•Acid test — If an acid and a base are mixed together, the result could be a
neutral substance.

•Vinegar test — If EITHER of the substances produces a positive reaction, the
mixture will do so also.

•Biuret test — A mixture of a substance that contains protein and another that
does not will turn a mix of purple and blue.

•Iodine test — A mixture of one substance that contains starch and one that
does not will produce a weak positive result — the solution will turn light gray.
b. Look carefully at the results of your tests. Is there a combination of
two of the known substances that could produce these results? If
so, what would that combination be? (28)
c. Continue testing tubes 7, 8, 9, and 10. What combinations of
known substances are present in each of the tubes? (29, 30, 31,
32)
3. The tubes from the back row (tubes 11 – 15) contain mixtures of THREE
known substances. Can you identify them?
a. Pick one of the tubes from the back row. Perform the five tests on
its contents. Record your results in a table. (33) What three
substances do you think are mixed here? Justify your answer. (34)
b. Challenge: Repeat the tests on the remaining tubes in the back
row. What combination of substances is in each tube? (35)
Unknown Appearance Litmus Vinegar Biuret Iodine
Substance (pH) (protein) (starch)
(powder or
crystalline)
#1
#2
#3
#4
#5
#6
#7
#8
#9
#10
#11
#12
#13
#14
#15
Further Analysis of Unknown Substances

In this activity, you will conduct the same five tests that you used in the previous activity. But, in this
case, you will encounter some substances that you have not seen before.

1. Click Reset. Under Select a sample, check Unknown. Then click New sample. Conduct
the complete set of tests on tubes 1 through 5. (36)
a. Did you find any substances that had properties unlike any of the substances that
you've seen so far? (37) In what ways did they differ? (38) (Note: At this point,
the contents of the tubes are randomized, so your results may differ from those
of your classmates.)
b. Give each of the new substances a name, like X, Y, or Z. What are the properties
of each of these new substances? (Acid or Base? React w/ vinegar? Protein?
Starch?) (39)
2. Challenge: Analyze the tubes in the second row. Again, they contain mixtures of two
substances.
a. Record your findings in the table below. (40)
b. What are the contents of each of these tubes? Explain how you know. (41)
3. Big challenge: Analyze the tubes in the third row.
a. Record your findings in the table below. (42)
b. What are the contents of each of these tubes? Explain how you know. (43)
Unknown Appearance Litmus Vinegar Biuret Iodine
Substance (pH) (protein) (starch)
(powder or
(Reset) crystalline)

#1
#2
#3
#4
#5
#6
#7
#8
#9
#10
#11
#12
#13
#14
#15
Assessment Questions

1. A substance is tested with litmus paper. The blue litmus paper remains blue while the red litmus paper remains red. What can you conclude about the substance?

A. The substance is an acid. B. The substance is a base.

C. The substance is neutral; it is neither an acid nor a base. D. The substance could be either an acid or a base.

2. Suppose that Biuret reagent turns purple when it is added to an unknown substance. What can you conclude about the substance?

A. The substance is an acid. B. The substance contains protein.

C. The substance contains starch. D. None of the above are valid conclusions.

3. Which of the following has a crystalline appearance?

A. baking soda B. salt C. baking powder D. corn starch

4. Given the data shown, what two substances does the unknown mixture contain?

A. Gelatin and baking powder B. Gelatin and baking soda C. Gelatin and corn starch D. Salt and corn starch

5. Given the data shown, what three substances might the unknown mixture contain?

A. Baking powder, baking soda, and corn starch B. Baking soda, corn starch, and salt

C. Corn starch, gelatin and salt D. Gelatin, corn starch, and baking soda