Appendix Z: CATs TQE LA V Laboratory Experiment—Mystery Solutions
Physical Science Unit Lab
Mystery Solutions
Date_________________,2006
Officer of Forensic Science Unit: _______________________________
Science requires careful observation. As observations are made, often
"patterns" emerge that lead to hypothesis and conclusions.
Forensic scientists use a variety of precipitation reactions - the formation of an
insoluble product. In this experiment, six known solutions of ionic compounds are
combined in all combinations. An ionic compound is one, which is formed from
positive and negative ions. When two solutions of ionic compounds are mixed,
the attraction may be strong enough to cause a solid (precipitate) to be formed.
Example 1 Sweat from fingerprints (NaCl) on rough surface such as wood and
investigator's spray (AgNO3) react and form white solid that turns black exposed
to sunlight. The chemical reaction can be written as:
NaCl (aq) + AgNO3 (aq) → NaNO3 (aq) + AgCl (s)
Example 2 The presence of sulfate ion can be detected in urine by precipatation
with the barium ion to produce barium sulfate:
Ba(NO3)2 (aq) + Na2SO4 (aq) → BaSO4 (s) + 2NaNO3 (aq)
Goal: Determine unknown chemicals collected from the crime scene.
Equipment:
-
Set of 6 known solutions in 5 mL pipets
-
Set of 6 unknown solutions in 5 mL pipets
-
Set of 5 unknown sample solutions from the crime scene in 5 mL
pipets
-
Laminated Table 1, 2, & 3
-
Paper towel
Grim Hunter, Nancy C.
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Appendix Z
Appendix Z: CATs TQE LA V Laboratory Experiment—Mystery Solutions
Procedure:
1. Obtain a set of 6 known solutions.
a.
Use the laminated Table 1 with the "dark" squares. Add one drop of
the chemical identified at the top of each column onto each dark square in
that column.
b.
Add a drop of the chemical identified at the side of each row onto
each dark square in that row.
c.
Record your observations in the Data Table 1 below.
Data Table 1: Known Solution Set
Known
set
Silver
Nitrate
Hydrochloric
Acid
Sodium
Carbonate
Lead
Nitrate
Sodium
Chloride
Potassium
Iodide
AgNO3
HCl
Na2CO3
Pb(NO3)2
NaCl
KI
Silver Nitrate
AgNO3
Hydrochloric
Acid
HCl
Sodium
Carbonate
Na2CO3
Lead Nitrate
Pb(NO3)2
Sodium
Chloride
NaCl
Potassium
Iodide
KI
Grim Hunter, Nancy C.
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Appendix Z: CATs TQE LA V Laboratory Experiment—Mystery Solutions
After the known solutions have been reacted, solve a set of unknowns
Labeled A thru F in order to practice your identification skills. The unknowns
are the same chemicals as the known set but in a different order.
2. Obtain a set of 6 unknown solutions.
a.
Use the laminated Table 2 with the "dark" squares. Add one drop of
the chemical identified at the top of each column onto each dark square in
that column.
b.
Add a drop of the chemical identified at the side of each row onto
each dark square in that row.
c.
Record your observations in the Data Table 2 below.
Data Table 2: Unknown Solution Set
Unknown
A
B
C
D
E
F
Set
A
B
C
D
E
F
What is the identity of each of the solutions?
A is ______________________.
D is ______________________.
B is ______________________.
E is ______________________.
C is ______________________.
F is ______________________.
Grim Hunter, Nancy C.
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Appendix Z
Appendix Z: CATs TQE LA V Laboratory Experiment—Mystery Solutions
Your next job will be to investigate crime scene sample solution unknowns by
the patterns observed earlier. Not only will you find the identity of the
unknowns, but also you will help to find what may have been used to possibly
murder the victim from the crime that occurred earlier this week.
3. Obtain a set of 5 unknown crime scene solutions and the set of 6 known
solutions from part 1.
a.
Use the laminated Table 3 with the "dark" squares. Add one drop of
the chemical identified at the top of each column onto each dark square in
that column.
b.
Add a drop of the chemical identified at the side of each row onto
each dark square in that row.
c.
Record your observations in the Data Table 3 below.
Data Table 3: Unknown Crime Scene Solution Set
Crime Scene
Unknown
Silver
Nitrate
Hydrochloric
Acid
Sodium
Carbonate
Lead
Nitrate
Sodium
Chloride
Potassium
Iodide
Set
AgNO3
HCl
Na2CO3
Pb(NO3)2
NaCl
KI
A
(Drink in
Mug)
B
(Spilled
Drops on
Table)
C
(Coffee in
Pot)
D
(Blood
Extract)
E
(Water Jug
on Counter)
Grim Hunter, Nancy C.
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Appendix Z
Appendix Z: CATs TQE LA V Laboratory Experiment—Mystery Solutions
What may be the identity or identities of each of the reactants found in the
solutions collected at the crime scene?
A is ______________________.
D is ______________________.
B is ______________________.
E is ______________________.
C is ______________________.
Are any of these possible reactants known to cause illness or death in
people? Explain.
Grim Hunter, Nancy C.
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Appendix Z
Appendix Z: CATs TQE LA V Laboratory Experiment—Mystery Solutions
Data Table 1: Known Solution Set
Known set
Silver
Nitrate
Hydrochloric
Acid
Sodium
Carbonate
Lead
Nitrate
Sodium
Chloride
Potassium
Iodide
AgNO3
HCl
Na2CO3
Pb(NO3)2
NaCl
KI
Silver Nitrate
AgNO3
Hydrochloric
Acid
HCl
Sodium
Carbonate
Na2CO3
Lead Nitrate
Pb(NO3)2
Sodium
Chloride
NaCl
Potassium
Iodide
KI
Data Table 2: Unknown Solution Set
Unknown
Set
A
B
C
D
E
F
A
B
C
D
E
F
Grim Hunter, Nancy C.
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Appendix Z
Appendix Z: CATs TQE LA V Laboratory Experiment—Mystery Solutions
Data Table 3: Unknown Crime Scene Solution Set
Crime Scene
Unknown
Silver
Nitrate
Hydrochloric
Acid
Sodium
Carbonate
Lead
Nitrate
Sodium
Chloride
Potassium
Iodide
Set
AgNO3
HCl
Na2CO3
Pb(NO3)2
NaCl
KI
A
(Drink in
Mug)
B
(Spilled
Drops on
Table)
C
(Coffee in
Pot)
D
(Blood
Extract)
E
(Water Jug
on Counter)
Grim Hunter, Nancy C.
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Appendix Z