Classification of Mystery Substances
This document supports the safety activity “Mystery Substance Identification: The
Identification of Unlabeled Chemicals Found on School Premises” from Flinn Scientific.
This is available on the Flinn Scientific website at:
http://www.flinnsci.com/media/755029/mystery.pdf
Background information
Your supervisor has just handed you a tray of containers filled with various materials.
Scattered on the bottom of the container are the labels that are suppose to be to be on
these bottles.
______________________________________________________
List of chemical labels in the box:
Mineral Oil Methanol
Sodium dodecyl sulfate (SDS)
Hydrochloric Acid
Hexane Hydrogen peroxide (10%)
_______________________________________________________
Your supervisor says she is worried there may be chemicals stored in the tray that are
incompatible. She wants you to identify the classes of substances in the tray so that they
can be stored properly while arrangements are made with the local chemical waste
disposal company.
General Classifications of Chemicals:
Acid: substance that increases the H+ ion concentration in aqueous solution
Base: substance that decreases the H+ ion concentration in aqueous solution
Oxidizing agent: substance that causes the oxidation (loss of electrons) of
another substance
Reducing agent: substance that causes the reduction (gain of electrons) of
another substance
Organic solvent: liquid made of carbon, usually in combination with hydrogen,
oxygen, nitrogen, and/or sulfur
Water reactive material: substance that can chemically interact with water
usually with a release of heat or light.
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This lab exercise concerns the characteristics and proper handling of various classes of
hazardous materials that may be found in a biotech lab. It is not intended to be training in
chemical identification. In fact, if you are presented with this kind of problem in the
workplace, you need to consult the Safety Officer for you company or institution.
Rather, this lab is a condensed version of the types of procedures that a professional team
would undertake when identifying a chemical. The simple tests are designed to assign
them to a broad classification for further identification and/or disposal. Pay attention to
both positive indicators as well as negative indicators in the testing procedures.
General Safety Precautions
Materials used in this lab may be hazardous; study the MSDS for each potential mystery
substance listed below. Choose one chemical at a time to work with. Wear gloves,
coat, and safety glasses. The reactions described are relatively safe. Therefore, unless
otherwise directed by the protocol, you may work either at your bench or in the chemical
hoods. Cover your work area with bench paper.
Laboratory Outline:
Day one:
1. Outline experimental protocol for lab
2. Research safety information on unknowns
3. Research chemical characteristics of unknowns
4. Classify unknowns (by chemical class)
Day two:
1. Complete testing of unknowns
2. Complete discussion in notebook: Disposal information is available
in the Flinn catalog.
Laboratory Notebook
You should include the following information in your laboratory notebook:
Safety information: A table of unknowns and precautions/ hazards for each
Chemical characteristics: A table of unknowns and their chemical properties
Disposal information: A table of each unknown and disposal method
Results: A summary table of each unknown tested, its physical characteristics, and
the results of all tests done
Discussion: 1. Determination of the probable identity of each unknown, along with
the reasoning used to reach this conclusion
2. Plan for how each unknown should be stored until it can be picked
up for disposal.
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APPENDIX: Protocol for identifying unknowns
Step 1. Make a preliminary inspection:

Check the container.
Is it a commercial container?
Describe the condition of the container. A primary inspection on the physical
characteristics may help in the identification of the material.
Has the liquid been prepared in the lab?
Does the bottle indicate the age of the material, when it was purchased, when it
was made? This information may give an indication of identity.

What are the physical characteristics of the material?
Solid: powder, crystal, granular, or another description
Color: homogeneous or heterogeneous? Check a color chart that gives an
indication of the identity of the material (for example, blue crystals may indicate a
copper compound or salt).
Liquid: color, viscosity

Open the container in a fume hood:
Is there any indication that the material reacts with the air? If so, the material
may be more dangerous than practical to handle. Stop the identification process
and call for professional help.
Write down all physical characteristics of the unidentified compound. Can any of
these physical traits give an indication as to the identity? These characteristics
may be needed to backup your conclusions from later tests.
Step 2. Exposure to water:
Is the material water reactive? Is the material water soluble?
TEST: Place about 3 mL of distilled water in a test tube. Add 2 drops of the liquid or
about 0.1 g of the solid to the water. Note any reaction. Carefully feel the test tube for
any temperature change.

Is the reaction violent? Does the reaction generate heat? Is the reaction exothermic
or endothermic? (what exothermic reactions are commonly found in the lab?) Label
as water reactive.
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TEST: After testing for water reactivity, mix 1 g of material in 10 mL of water. Look
for residue and estimate solubility (insoluble, partially soluble, or soluble)

Is the substance water soluble? If yes, then proceed to step 3.

Is the substance water insoluble? If yes, and the substance is a liquid then proceed to
step 4 to determine density. If yes and the substance is a sold then label as water
insoluble and proceed to step 6.
Step 3. Check the pH:
TEST: With pH indicator strips use a Pasteur pipette to remove a drop of the liquid from
the aqueous solution prepared in Step 2. Place on the indicator strip and determine the
pH using the scale provided on the box. Record the pH.
1. Is the pH below 3 or above 11? This indicates that the material is a corrosive
material and should be labeled as a “Corrosive acid” or “Corrosive base.”
2. A pH between 3 and 5 indicates the following possibilities:
1. Weak acid
2. Dilute strong acid
3. Salt of either a weak base or a strong acid
In this case the material can be disposed of by neutralizing the material by
titration with a base and disposal down the sewers.
3. A pH between 8 and 11 indicates the following possibilities:
a) Weak base
b) Dilute strong base
c) Salt of either a weak acid or a strong base
(Note: With an alkaline pH there is a possibility that the compound is a sulfide or a
cyanide compound. If either of these is neutralized there is a possibility that cyanide gas
or hydrogen sulfide gas will be generated. To test for these possibilities add dilute
calcium chloride (0.1 M) to the solution in the test tube. If a white precipitate forms, you
most likely have a phosphate or carbonate compound as a salt. Unless a precipitate forms
assume the material is hazardous and do not proceed. Call a hazardous materials
specialist. The presence of the precipitate indicates that the material can be neutralized
with acid and disposed of through the sewer system.)
Step 4. Density:
The density of a liquid can be determined by weighing a known volume. Determine the
mass of a small weigh boat or use the tare button on the balance. Pipette one mL of the
liquid into the weight boat. Record the mass and subtract the mass of the weigh boat.
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Repeat this more two times and average the mass. Density is recorded in weight per
volume (g/mL).
a. If the material is water soluble, and is less dense than water it will probably be
a low molecular weight alcohol.
b. If the material is water soluble, and has a density that is greater than water it
may indicate a concentrated acid.
c. If the liquid is not water soluble, and is less dense than water, it may be:
 A hydrocarbon (hexane, pentane)
 Fat (cooking oil, mineral oil)
 High molecular weight alcohol or amine
d. If the liquid is not water soluble, and is more dense than water, it is likely to
be a halogenated hydrocarbon (chloroform).
Step 5. Oxidizing or reducing agent:
a. For a water-soluble material lower the pH to 5-7 with a small quantity of acid.
Add a drop of the pH adjusted solution to about 1 mL of an aqueous 1 M
potassium iodide solution. If a yellow color develops, then label the material
as a water soluble oxidizing agent.
b. Prepare a solution of the material at a concentration of 50 mg / mL. Add the
solution drop wise to a dilute 0.1 mM potassium permanganate solution. If
the potassium permanganate solution changes from a pale pink color to clear,
then label the material as a reducing agent.
Step 6. Check for flammability:
a. Dip a glass rod into the liquid material and expose to an open flame.
b. Take a small piece of solid material and expose to an open flame.
c. If a flame develops then label as Flammable. Also note the color of the
flame.
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