Hands-on Activity: Introduction This multipart activity was designed to have minimum student directions
to allow for hands-on, inquiry-based explorations by students. The activity
is set-up by having students read about the early history of aspirin in
Aspirin Adventures. Particular attention should be paid to the Aspirin
Intrigue section. In the early part of the twentieth century many
unscrupulous entrepreneurs were anxious to profit from the new aspirin
market by making "counterfeit" aspirin. Their illegal product labels
proclaimed ASA when the actual product was possibly aspirin mixed with
cornstarch or flour, unreacted salicylic acid blended with a sodium salt, or
just cheap, white, safely ingested solids.
This lab requires two substances generally found in high school and
college chemistry stockrooms. Beral® pipettes are useful but not
mandatory items. The other reagents and supplies are readily available
consumer items. The two reagents you will need to purchase from a chemical
supply house are:
Spring 2000 list prices with educational lab suppliers such as Fisher
Science Education, Sargent Welch, and Flinn Scientific are approximately
$7-8 dollars plus shipping for 100-gram quantities of either salicylic acid
crystals or ferric chloride hexahydrate. If anhydrous ferric chloride solid
is available for use, it will also work. The iron chloride compound must
contain the iron in the +3 oxidation state, which is indicated by either
iron(III) or ferric designation. The +2 oxidation state iron(II) or ferrous
or Fe+2 compounds are to be avoided, as these
are not suitable for use in these activities.
The solid reagent iron(III) chloride hexahydrate, FeCl3·6H2O, is a skin and
tissue irritant. It is corrosive and slightly toxic by ingestion with a
LD50 of 1278 mg/kg, according to Flinn
Scientific. The shelf life is fair to poor as it is hygroscopic. Flinn
Disposal Method 26a: Solid Waste Disposal in Landfill is indicated in the
1999 Flinn Scientific Catalog. According to the Fisher Scientific MSDS for
FeCl3·6H2O,
this substance may cause central nervous system effects, cardiac
disturbances, liver and kidney damage, and severe eye irritation.
Flinn Scientific lists the solid salicylic acid, 2-HOC6H4COOH, as moderately
toxic by ingestion with a LD50 of 891 mg/kg.
Fisher Scientific MSDS indicates this substance is light and moisture
sensitive. Contact with eyes and skin may cause severe irritation and
possible eye and skin burns, especially if the area is wet or moist. Flinn
Disposal Method Number 24a for Organic Acids is cited in the 1999 Flinn
Scientific Catalog.
Local, state, and federal regulations are constantly changing and all
disposals of hazardous substances should be consistent with these
regulations.
Teacher and students should:
MSDS Sheets for Reagents Used
The following MSDS sheets are available on-line from Cornell University:
Requirements of test reagent using FeCl3
or iron(III) chloride: A dilute solution will work. Either 0.1 molar (0.1 M)
FeCl3 or 1% FeCl3 solution is acceptable if available. To quickly make a
rough approximation of these concentrations do the following: add an amount
of solid FeCl3 approximately equal to size of
an aspirin tablet to a clean 9-ounce labeled cup. Fill the cup two-thirds
with water (approximately 200 ml) and swirl to dissolve as much of the
iron(III) chloride as possible. Use the solution to fill the
Beral® pipettes. The solution produced should be golden or orange
brown in color. If a few tiny particles do not dissolve, that is okay.
When the golden brown FeCl3 solution is
dispensed from a Beral® pipette onto white salicylic acid, a dark
purple color will immediately appear. This is due to the formation of a bond
between the Fe+3 ion and the phenol group on
the SA molecule. The Fe+3 ion will form six
such chemical bonds with the phenol groups of six different SA molecules.
The Fe+3 ion is said to form a complex ion.
This process is known as complexation.
Aspirin (ASA) will not immediately produce a dramatic color change.
However, ASA, which is not very soluble in water (1 gram ASA dissolves in
300 ml of water at room temperature), will slowly react with water to
produce SA and acetic acid. Perhaps you have noted that aspirin tablets,
when exposed to moist air, will produce the faint odor of vinegar, which is
5% acetic acid. As a result of the slow hydrolysis reaction, the purple
color slowly appears, indicating the complexation of iron(III) ions and free
phenol group of the SA.
Select an even number of groups. Two groups will interact in Part V.
Role assignments: Best group size is three to four members. For a
three-member group, combine the first two roles. For five-member group, add
a second Supply Manager.
Individual group setups:
* Solo Brand plastic cups were used in the development of these
activities. Lab glassware and other plastic containers may be substituted
for these cups.
Central Supply Station:
Optional suggestions of other possible pain relievers:
Part I
Student Supply Manager should place one whole tablet of the each of the
required seven pain relievers in the first group above in the correct,
labeled clear cup. Place a very small amount of salicylic acid in the
seventh cup. Assemble the cups in a row. Record the visual appearance of
each substance. After the row of cups is assembled, carefully pour in
approximately 60-75 ml of water (one fourth of the cup height for the
9-ounce clear cup or approximately 2.0 cm water depth.) Try to have the
water levels approximately equal in each of the cups. Observe every few
minutes. Record observations. The tablets will start to slowly disintegrate
as any coatings or water-soluble binders are removed. Most of the active
components are not water soluble, but the coatings and most of the binders
are water-soluble. Note any color changes in the water. Note the difference
in “clear” (everything dissolves and the water is clear with no solid
particles in sight), and “colorless” (complete absence of color). Note how
the tiny particles remain close to each other. There is very limited
dispersion of the main insoluble components. Try not to disturb the
containers as you observe them. These cups and their contents will be used
later in Part IV after you complete Part II and III.
Salicylic acid has limited solubility in water. Only 1.0 gram of SA will
dissolve in approximately 500 ml of water at room temperature. Recall that
1.0 gram of acetylsalicylic acid, ASA, will dissolve in 300 ml of water at
room temperature.
Part II
Students should place a piece of the appropriate tablet in a labeled
white, 3 ounce disposable plastic cup. The white opaque cup is chosen to
enhance any color changes. Clear containers may be substituted. If these are
used, the containers be should placed on a clean sheet of white unlined
paper to provide a background similar to white opaque cups to make color
changes easy to see.
Required to test first should be the six pills (small cut pieces) plus
salicylic acid powder:
The Student Tester should squirt several milliliters of FeCl3 solution onto each pill piece and onto the salicylic
acid powder. The SA will immediately produce a dark purple color. After some
time has lapsed, the acetaminophen will produce a purple color due to the
presence of a phenol group in the molecular structure. It should be noted
that Tylenol or acetaminophen was not in use in the early part of the
twentieth century, but it is included here as it is on the "required list."
In addition, some pills with colored coatings show a slight purple color
when treated with iron(III). This is possibly due to the presence of phenol
groups in FD&C Yellow #6. When hydrolysis has had a chance to occur on
the aspirin or ASA tablets, a paler purple color will be observed.
Optional: let the groups select small pieces of three additional
different, nonaspirin modern pain relievers and test these in clean cups
using iron(III) chloride if time permits.
Part III
This section tests possible additives to aspirin tablets. These will be
white powders or crystals. Some are water-soluble; some are not. All are
substances available in 1900 as well as today.
Select five different substances, choosing at least one from each of the
three different group categories that follow below. Transfer a very small
amount of each white powder (equal approximately to one fourth the size of
an aspirin tablet) into the correctly labeled cup.
White powders safe for human consumption, which were often used in
making the “fake aspirin.” Listed first below are two kitchen substances
available at the turn of the century that are similar in appearance and
water solubility to salicylic acid:
Group 2
Other white additive possibilities were:
Group 3
Additional white powders that physically look like salicylic acid and
could be explored by students:
Students should test each of the five white substances selected by adding
1-2 ml of iron(III) chloride in the Beral® pipettes. Pipettes may
be refilled at the Central Supply Station. Any color changes should be
recorded.
Part IV
Have the students observe the tablets that are in water in the larger,
clear containers. Carefully note the changes in appearance. After these data
are recorded, pour several milliliters of FeCl3 into each cup. Record what happens immediately. The
acetaminophen (Walgreen's generic is interestingly labeled “No Aspirin”)
will turn purple. This is due to a phenol group in the structure. Have the
students locate the structure in the reading A
Festival of Analgesics. The ASA tablets will have a pale purple color
develop on standing due to the hydrolysis of the ASA, which produces SA.
Ibuprofen, Aleve®, and Orudis KT® will not turn
purple. Encourage students to check the structures of the substances chosen
to see if there are phenol groups present on molecular diagrams.
Part V
Pair the teams. Assign one team the role of “making” aspirin powder. The
other team will be the “testers” and design and implement tests to discover
if the “aspirin powder” is legitimate aspirin or if it contains significant
amount of unreacted salicylic acid.
NO TASTING WILL BE ALLOWED by either the makers or the testers.
Each team is asked to design a cover that might have been used in the
early twentieth century for the “pain product” the groups designed and
tested. There will be the folded paper to contain the aspirin powder as well
as a small box or envelope that will contain the folded aspirin doses.
From the tests they have run on known tablets and possible adulterants,
the students should be able to distinguish real aspirin from salicylic acid
and from other substances posing as aspirin. The following observations can
form the basis of a reasonable test of the mystery powder:
Part VI
Place a 1-inch or larger common nail into the bottom of a clear plastic
cup. The nail must not be galvanized (coated with zinc). Add a very small
amount of salicylic acid. Cover the nail completely with water. Let it sit
undisturbed at least overnight. By the next day, the liquid will be a purple
color. Why ?
First ask: what is the nail made of?
Second ask: where have you seen this color before ?
Next ask: what do you think has happened here?
The common nail is made of iron. The iron reacts with the water
overnight. This is the beginning stage in the formation of rust. The process
is often referred to as corrosion. Necessary for this corrosion of iron is
the presence of both oxygen, O2, and water,
H2O. First, the iron atoms on the surface of
the nail loose two electrons to form Fe+2
ions. Next, the Fe+2 ions that move close to
the surface of the water encounter O2
molecules that have dissolved into the water from the air. The O2 molecules oxidize the iron(II) ion to an iron(III)
ion, Fe+3 ion. This is the ion that complexes
with the phenol group on the salicylic acid.
If you want to explore this further, you can set up two cups, using two
identical nails. Add SA to each. Add table salt to one cup. Next, add water.
See if there are any differences the next day. Note: iron corrodes much
faster in salt water.
Yet another variation, have two cups, two nails. Add SA to each cup.
Next, place several ml of vinegar (acetic acid) in one cup. Then add water
to both cups so that the level of liquid in both cups is equal. Observe for
possible differences over time.
To help grade lab reports, you may choose to use this rubric. One way to
use the rubric is to apply it to each individual section of the lab report
(there should be six sections, for Parts I-VI of the activity). Using this
rubric, each section would be worth 56 points, for a total of 90 points.
For more information, at other Web Sites...
Relevant National Science Education
Standards
Science as
Inquiry — The activity involves scientific inquiry, decision-making,
and problem-solving.
Physical
Science — The structure of molecules is a central concept to the
activity, as is the concept of chemical reactions, specifically the
complexation reaction of FeCl3 with
molecules containing phenol groups.
Science and
Technology — The readings demonstrate how a scientific principle can
be applied in solving a practical problem, namely identifying compounds
disguised as aspirin.
History and
Nature of Science — The historical perspective is central to the
activity. Relevant New Jersey State Science
Curriculum Standards
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Achievers Home
Real or Phony?
Materials
and Apparatus
Safety
The
Iron (III) Test
Suggested
Set-up for Activity
Lab
Report Assessment Rubric
Relevant
National Science Education Standards
Relevant
New Jersey State Science Curriculum Standards
Container Labeler
Supply Manager
Tester
Reporter
Required:
To keep the cost low for this lab activity, we suggest
that the tablets be cut into several pieces for Part II. Ordinary scissors
will easily cut round tablets into two to four pieces and oblong caplets
into two or three parts. For the colored tablets, note if the center of the
tablet is a different color from that of the surface color.
FD&C Yellow #6 Group 1
Points
Report
Report describes all observations noted on worksheet
completely, thoroughly, and clearly.
Report describes all observations completely.
Report describes most observations completely.
Report describes most observations.
Report describes some observations.
Report does not describes observations.
Conclusions
Makes reasonable conclusions that are well explained.
Makes reasonable conclusions that are somewhat
explained.
Makes reasonable conclusions that are not explained.
Makes some conclusions but offers no explanation.
Makes some conclusions but some are not reasonable and
are without explanation.
Does not make any conclusions.
Grammar, etc.
The student has no grammatical errors or misspelled
words in the report.
The student has few grammatical errors or misspelled
words in the report.
The student has some grammatical errors and misspelled
words in the report.
The student has several grammatical errors and
misspelled words in the report.
The student has many grammatical errors and many
misspelled words in the report.
The student has many errors making it difficult to
understand the content of the answers. 3 Fake Drugs Are Found in Pharmacies — from the New
York Times, 5 June 2001.
Unifying
Concepts and Processes — The activity reinforces that the parts of a
system contribute to its overall behavior, specifically that a phenol
group in a molecule's structure will bring about a purple color in the
presence of FeCl3.
5.1
The activity involves scientific inquiry, decision-making,
and problem-solving.
5.4
This activity involves a test of practical value that is an
application of scientific principles.
5.6
The molecular interactions of phenolic compounds with iron
(III) chloride are central to the activity.
This activity was developed by Professor Johnnie-Marie Whitfield,
Millsaps College.