Organic Unknown Analysis
NOTE: There is no pre-lab assignment for this lab experiment. Also, the lab report for this
experiment will be different than the standard lab report format shown on your syllabus; see the
section entitled “Lab Report” on the last page of this document for further details.
PURPOSE OF THE EXPERIMENT
To identify an unknown compound (or compounds) by a combination of qualitative, quantitative,
and spectral analysis.
BACKGROUND REQUIRED
You should be familiar with the interpretation of IR and NMR spectroscopy.
BACKGROUND INFORMATION
Qualitative analysis refers to the determination of a compound formula based on the qualitative
properties of the compound, as opposed to the quantitative properties. In general, qualitative
properties are those which are independent of the amount of the compound present, do not require
numerical measurement for their determination, and usually describe the behavior of the
compound. Color, odor, and solubility in water (or another solvent) are all examples of
qualitative properties. These qualities are not dependent on the size of your sample. Most
qualitative analysis involves performing chemical reactions in the course of analysis; for instance,
to test for flammability involves burning the compound, which is a combustion reaction.
One simple qualitative test is to measure the solubility of the unknown in water, aqueous acid,
aqueous base, or organic solvents. The solubility properties of compound, and the pH of the
resultant solution, can often indicate particular functional groups.
Many qualitative tests are specific to a particular functional group. In this experiment you will
perform a number of tests that are designed to differentiate one functional group from another,
and which may be used to determine the functional group(s) present in your unknown compound.
The Tollen’s test, for instance, is a chemical reaction that only occurs at an aldehyde
functionality. The reaction may serve as a test for the presence of aldehydes because the reaction
produces a deposition of silver metal at the bottom of the reaction container; if you mix the
proper reagents with an unknown compound and observe the deposition of silver, then you know
your compound is an aldehyde, or contains an aldehyde group. (The specific procedure for the
Tollen’s test is given in the procedure section). It also should be noted that if this reagent mixture
does not produce the silver deposition, one may conclude that the compound does not contain an
aldehyde functional group. As you perform your tests in this experiment, remember that
“negative” test results can aid in your identification just as much as “positive” results!
Quantitative tests require the measurement of numerical information. Some simple examples of
quantitative properties are density, melting point, boiling point, specific gravity, and viscosity.
While most of the tests performed in this experiment are qualitative tests, there are a few
quantitative tests which are simple to perform and may greatly aid in your identification of the
unknown compound. Depending on the phase of your unknown (solid or liquid), you will
measure the melting point or density of your sample.
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Your instructor will also provide you with spectral analyses of your compound, which may
include infrared spectra, H-NMR spectra, and/or 13C-NMR spectra. These spectra may of course
be used to aid in the identification of the compound’s functional group, or to confirm the results
of your chemical testing.
Here are some general comments to remember as you perform this experiment:
 Most of the test are qualitative; which means that the amounts of chemicals that you add do not
need to be measured very precisely. If you add a little too much or too little of your unknown
or a particular reagent, it will generally not affect the results of the test. Don’t waste time
cleaning out your graduated cylinder numerous times during the experiment! You will not
need a graduated cylinder for most of these tests. Unless otherwise indicated, all quantities in
these tests are approximate. Note that the plastic eyedroppers provided for you have
markings for 0.5 mL, 1.0 mL and (for some eyedroppers) 2.0 mL on the stem of the dropper.
For the tests in this experiment, these approximate volumes are perfectly acceptable.
 There are obviously a large number of different reagents and solutions used in this experiment.
Please remember to re-cap bottles and replace the eyedroppers on the proper bottle when you
are finished using them! Cross-contamination ruins your results AND everyone else's!
 It is not necessary to perform the tests in the order given in this experiment. Each test provides
you with an individual piece of information to help you identify your unknown. It really
doesn’t matter in which order you collect the test results.
 It will be very important for you to consult a reference to assist in determination of your
unknown. Available in the lab will be a copy of the Merck Chemical Dictionary, which can
provide you with a physical data (melting point, density) and structures for a wide variety of
chemical compounds. A similar resource is available online at www.chemfinder.com. For
many organic compounds, structure and simple physical data (such as melting point and
density) can be found on Wikipedia. Once you have a compound that you think might be
your unknown, you should certainly look it up in one of these references – they may provide
you with confirmation of your guess! Make sure you compare the literature values for
melting point and density to those that you measure in the lab.
 Keep in mind that you do not necessarily have to perform ALL these tests! Only perform the
tests that you feel are necessary to identify the unknown. If you feel that you are certain of
the identity of you compound, you don’t need to test any further. If, for instance, you have
conclusively demonstrated that your compound is an aldehyde, then there is no reason to
perform a chromic acid test.
 Good record-keeping is essential in this experiment! Students who jot down their results on
scrap paper or trust their memories generally have problems later when they try to identify
their unknown. You will be gathering together the conclusions from a series of tests in order
to make your final assignment; it is essential that you have very clearly recorded the results
and conclusions of each test.
 Several of the tests below indicate a positive result by the formation of a precipitate.
Sometimes precipitates are formed as very fine crystals, which may take a long time to settle
from solution (as opposed to large chunks, which settle immediately to the bottom of the test
tube). Please note that if a solution turns cloudy or opaque, that is an indication that a
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precipitate is present. Solutions are always transparent; if you see a cloudy mixture, there is
a precipitate in the liquid.
Unknowns - Some General Information
All of the unknowns contain only one of the oxygen or nitrogen containing functional groups. (In
other words, you will not receive any bifunctional compounds, such as a hydroxy-substituted
acid, or a compound that contains both ketone and aldehyde functionalities). In addition, the
unknown may contain halogens, aromatic rings or sites of unsaturation.
Please be aware that although there are no bifunctional compounds, some of the unknowns may
be difunctional compounds. In other words, dicarboxylic acids, diols, dienes, etc. So you will
NOT receive any compounds that have both an alcohol and a carboxylic acid, but you MAY
receive one which has two alcohol groups on the same molecule, or one which contains two
carboxylic acid functional groups on the same molecule.
You will receive two unknowns, a different one each week of the experiment:
Unknown #1 - You only need to identify the functional group of the compound; it is not
necessary to determine the actual structure or name of the compound.
Unknown #2 - The unknown will be one of the compounds on a list provided in the lab by your
instructor. You will need to specifically identify the compound. Provide a structure and/or an
IUPAC name for the unknown. You will receive spectral information about the unknown after
you have correctly determined the functional group.
Spectral Analysis
For some of the unknowns, you may be provided with IR and/or NMR spectral data. After you
have determined the functional group of your compound, your instructor will provide you with
the spectra for your unknown if they are available. When you think you know what functional
group is present, tell your instructor and he will check your result. If you have correctly
identified the functional group of your unknown, you may proceed with spectral analysis.
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PROCEDURE. The procedure section of this lab is divided into three sections: Physical Tests,
Functional Group Tests, and Structural Tests.
Part 1: Physical Tests
These are simple tests in which you determine physical properties of your unknown such as solubility,
melting point, and density. Solubility will aid you in determining the functional group; melting point and
density will aid you in identifying the exact structure of your compound after you know the functional
group.
Solubility Tests
The first thing you should do with your unknown is determine it’s solubility class. A flow chart
for the determination of solubility class is given below in Figure 1. The solubility class will give
you an idea of the functional group of your compound; but remember that solubility tests are only
an indication or a starting point, and functional group tests MUST be made to confirm the
functional group of your compound.
Unknown
H2O ?
insoluble
soluble
pH of solution?
2.5 M NaOH ?
insoluble
soluble
1.5 M NaHCO3 ?
1.5 M HCl ?
Acidic pH
(pH 4 or less)
(pH 9 or greater)
carboxylic acid
amine
Basic pH
Neutral pH
alcohol, aldehyde, ketone, ester
soluble
carboxylic acid
Class A1
insoluble
soluble
insoluble
most phenols
Class A2
amine
Class B
Class S
( 5 Carbons or fewer)
conc. H2SO4 ?
insoluble
alcohol, aldehyde, ketone, ester
( 5 Carbons or more)
soluble
hydrocarbons (including aromatic
and unsaturated), alkyl halides
Class N
Class I
Figure 1: Solubility Classification Scheme
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It should also be noted that, while solubility tests are very helpful in general, there may be
difficulties with specific unknowns. Solubility tests are not always easy to interpret, because
partial solubility can be difficult to distinguish from insolubility. Also, sometimes there is a
REACTION between the unknown and the solvent being tested, which doesn't allow completion
of the solubility testing process. If your unknown reacts with the solvent, you cannot determine
its solubility in that solvent; in other words, the solubility test ends there. (If your unknown
reacts with the solvent, it will be evident as a change in color, formation of a precipitate, or other
changes in physical appearance). However, solubility testing is a good place to start; it may help
you decide which chemical tests to perform.
Testing Solubility: To perform a solubility test, place about 10 – 12 drops of a liquid unknown or
0.1 g of a solid unknown into a clean test tube. (0.1 g of a solid is a small scoop; enough to cover
the end of a spatula. You don’t have to weigh it). Add, in small portions, about 3 mL of the
solvent being tested. Between each addition stir the sample vigorously with a clean glass stirring
rod or spatula; with solids, you should use the end of the stirring rod or spatula to crush the
crystals into a fine powder. Soluble solids will dissolve to form a transparent solution; liquids
will dissolve to form a single phase liquid mixture (as opposed to two immiscible layers). If your
unknown has a color, then solubility will be easier to determine because colored solute will
change the color of the solvent (blue solutes will produce blue solutions, brown solutes will
produce brown solutions, etc.). So be sure to note if the solvent develops a color similar to the
color of your unknown - this would certainly indicate solubility in that solvent.
If you are uncertain of the result, try warming the mixture gently in a warm water bath; heating
will generally increase solubility.
Testing pH for water soluble unknowns: You will see from the flow chart that if your sample is
water soluble, the next step is to determine the pH of the resulting solution. In order to record an
accurate pH, it is important that the concentration of the unknown be relatively high. So
BEFORE you test the pH of an aqueous solution, you should add a few extra scoops of your
unknown (if it’s a solid) or about 2 extra mL of your unknown (if it’s a liquid).
Quantitative Tests (Density / Melting Point)
If your sample is a solid, determine it’s melting point by the standard method of m.p.
determination.
If your sample is a liquid, the density of the liquid can be easily determined. Using a 5 mL
pipette, carefully measure out exactly 5 mL of your sample into a clean, dry, pre-weighed
container. If you take the mass (in grams) of this 5 mL sample, and divide by 5, it will give you
the density of the sample in the standard unit of g/mL. (Note that a 10 mL pipette can also be
used, and the mass divided by 10).
Part 2: Functional Group Tests
Below are tests for specific functional groups; this will allow you to determine if your compound
is a ketone, alcohol, aldehyde, etc. If you wish to perform a control test, you should do it
simultaneously with your unknown. Your instructor will provide you with a standard to use for
control test if you wish.
 Chromic Acid Oxidation Test (for primary and secondary alcohols, or aldehydes): Primary or
secondary alcohols can be oxidized to carboxylic acids or ketones, respectively, by a mixture of
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dichromate ion and sulfuric acid. Aldehydes are also oxidized to carboxylic acids under these
conditions. The actual reaction is between the alcohol (or aldehyde) and chromic acid, H2Cr2O7,
which is formed in situ when the dichromate and sulfuric acid are mixed:
H2Cr2O7 + ROH  Cr2(SO4)3 + RCOOH (or R2C=O)
The acid reactant is orange in color; the chromium (III) sulfate product is blue-green in color. It
is the formation of this blue-green (which will sometimes precipitate) that is a visual indication
that an alcohol or aldehyde is present.
To 5 mL of a 1% solution of sodium dichromate, add 1 drop of concentrated sulfuric acid and
mix thoroughly by shaking. This is a very corrosive mixture, do not allow it to contact your skin!
Add 2 mL of your unknown liquid (or about 0.5 g of unknown solid) and warm in a hot water
bath. The development of emerald green color in the solution, or the formation of a blue-green
precipitate, is a positive test for primary or secondary alcohol, or aldehyde. This reaction may
take as long as 10 - 15 minutes. Note that tertiary alcohols will not react with chromic acid. The
waste from this test should be discarded in the waste container!
As you should know from lecture class, chromic acid will also oxidize aldehydes to carboxylic
acids; that is generally a slower reaction and some aldehydes will not give a positive chromic acid
test, but many will. Therefore, the chromic acid test should always be performed along with the
Tollens’ test (see below) to verify the functional group of the unknown. You can only conclude
that the compound is an alcohol if it gives a NEGATIVE Tollen’s test.
If you have determined that your compound is an alcohol, you may wish to perform the Iodoform
test next, which distinguishes certain alcohols from others; this is helpful if you are trying to
identify the specific identity of your compound. It is NOT necessary if you are only trying to
determine the functional group.
 Tollen’s Test (Silver Mirror Test) for aldehydes: This test involves the reduction of an alkaline
solution of silver ammonium hydroxide to metallic silver, with the concurrent oxidation of the
aldehyde to a carboxylic acid:
Ag(NH3)2
O
R
C
H
H2O
O
R
C
-
O
+
Ag
(silver mirror)
This is called the “silver mirror test” because the silver is deposited on the bottom of the test tube
in a thin, reflective layer. (see section 18-20 in your lecture textbook for more information on the
Tollen’s test, and a photograph of how a positive result looks). Alcohols and ketones, if pure, do
not react in the Tollen’s test. However, some alcohols, when stored, will oxidize in air to form a
small amount of aldehyde, which may deposit small flecks of silver on the test tube. This “false
positive” is usually pretty easy to distinguish from a true aldehyde, which will cover the entire
bottom of the tube in silver.
Note: This test may exceed 20 or 25 mL, so you should perform the test in a LARGE test tube. In
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order for the silver to deposit as a mirror, the test tube must be thoroughly cleaned, with a brush,
soap and water.
Place 1 mL of a 5% solution of silver nitrate and add a drop of 10% aq. NaOH in a clean test
tube. Add a 6 M solution of ammonia, drop-by-drop with constant shaking, until the precipitate
just dissolves. It is important to avoid an excess of ammonia; stop adding as soon as the
precipitate dissolves!
Add 2 drops of the unknown, shake the tube, and heat the solution to 40C in a hot water bath for
about 15 - 20 minutes. A positive result for aldehyde is the formation of a mirrored surface on
the bottom of the test tube (if it is clean! A finely divided black precipitate silver will be observed
in a test tube that is not thoroughly clean). The waste from this test should be discarded in the
waste container!
Part 3: Structural Tests
Once you have determined your functional group, these tests will assist you in determining the
structural features of the compound. For instance, does your compound have any halogen atoms?
Double bonds? Triple bonds?
 Iodoform test (for alcohols with the structure RCHOHCH3 or HCHOHCH3, or
ketones with the structure RCOCH3):
This test identifies oxidized carbons (carbons with alcohol or ketone groups) which also have
methyls attached to them. Other types of alcohols and ketones will NOT give a positive
iodoform test.
The test depends on oxidation of the alcohol to RCOCH3, which reacts with iodine to give a
bright yellow precipitate of iodoform. Note that a methyl alcohol will be oxidized to a methyl
ketone, which will then produce iodoform. If the unknown is a methyl ketone to begin with, then
the reaction begins with the second compound:
OH
R
C
O
O
CH3
HO
I2
NaOH
R
C
CH3
R
base
C
H
C
-
I
I
I
O
R
I
C
OH
+
C
O
-
I
R
C
O
-
+
HCI 3
(yellow)
I
Note that only alcohols with an adjacent CH3 group will react! This test could be used, for
example, to distinguish between 2-pentanol and 3-pentanol; only the first alcohol would give a
positive iodoform test. It could also be used to distinguish acetone (which would give a positive
iodoform test) from pentan-3-one (which would give a negative iodoform test).
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In a clean, acetone-free test tube, mix 3 drops of the liquid unknown (or about 50 mg of the solid
unknown) with 2 mL of water and 2 mL of 10% aqueous NaOH. Add, drop-by-drop while
shaking, a 10% solution of iodine in KI, until a definite brown color persists (indicating an excess
of iodine).
With some compounds a yellow precipitate of iodoform will appear almost immediately. If no
precipitate forms after 5 minutes, heat the test tube to 60C in a water bath. Add more iodine, to
keep the solution brown, if necessary. A positive result is the formation of lemon-yellow crystals
of iodoform. The waste from this test should be discarded in the waste container!
 Alcoholic Silver Nitrate test & NaI test for alkyl halides: These are tests that should be
performed on all week 2 and week 3 unknowns, regardless of their functional group, to test for
the presence of chlorine or bromine. Both tests are nucleophilic substitutions reactions. The
alcoholic AgNO3 test proceeds by an SN1 mechanism, and the NaI test proceeds via SN2.
It is worthwhile to perform both of these tests, because for an SN1 mechanism (like the AgNO3
test, the order of reactivity of alkyl halides is:
tertiary > secondary >> primary
so this test will not necessarily detect primary alkyl halides (they react VERY slowly in SN 1
reactions). On the other hand, for the NaI test (with an SN2 mechanism), the order of reactivity is
reversed – primary alkyl halides react very quickly, but tertiary alkyl halides may not react at all.
So to thoroughly test for the presence of a halide, both tests must be performed.
Alcoholic Silver Nitrate test: In a test tube place 2 mL of a 2% solution of silver nitrate
in ethanol and add one drop of the liquid unknown (or 10 mg of solid unknown). A positive
reaction is the formation of a white or off-white precipitate of silver halide within 5 minutes. If
no reaction occurs after 5 minutes, boil the solution gently for 5 minutes.
A possible interferent in this test is the formation of silver salts of organic acids; if your unknown
is a carboxylic acid it may form a precipitate under these conditions, even if there is not halide
present. If a precipitate forms during this test, you must test the solubility of the precipitate in
acid by adding 2 drops of dilute nitric acid. Acid salts will dissolve; halide salts will not. So if
the precipitate dissolves in the nitric acid solution, there is NOT a halogen present in the
compound.
Sodium Iodide in Acetone test: This test is a nucleophilic substitution reaction in which
iodide ion replaces chlorine or bromine on an alkyl halide:
RX + NaI 
RI + NaX (solid)
where X = Cl or Br. Sodium halide salts are insoluble in acetone, which is the solvent for this
test.
In a small test tube, dissolve 2 drops of liquid unknown (or 20 mg of solid unknown) in a
minimum volume of acetone and add 1 mL of the NaI test solution. A positive result is the
formation of a white precipitate of sodium halide. If no precipitate is observed within 5 minutes,
heat the mixture in a hot water bath for about 5 minutes, then cool to room temperature and see if
a precipitate forms.
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
Permanganate test (Baeyer test) for alkenes and alkynes: This tests for non-aromatic
carbon-carbon double bonds or triple bonds. Almost all alkenes and alkynes will oxidize in the
presence of permanganate ion to a diol:
3 H2C
CH2
+
2 MnO 4-
+
4 H 2O
3
CH2
HO
CH2
+
2 MnO 2
+
2 OH-
OH
However, you should note that some aldehydes and ketones will also give positive results in the
Baeyer test! Although the reaction is different for aldehydes and ketones, the visual indication of
a positive test is the same; in other words, the permanganate color will disappear. (If your
compound is an aldehyde or ketone, this test will not be conclusive).
In a small test tube, dissolve 3 drops of the liquid unknown (or 30 mg of solid unknown) in 1 mL
of PURE (alcohol free) acetone. It is advisable to run a control with just acetone to ensure that
there are no impurities in the solvent. Add dropwise, with vigorous shaking, a 1% solution of
potassium permanganate. A positive result is the loss, within 1 minute, of the purple
permanganate color and the formation of a brown or gray precipitate of MnO2.
Writing Your Lab Report
EACH UNKNOWN should have its own report.
sections:
The report should contain the following
Name and Date
Identity of your Unknown: Unknown analyses are different than most lab reports in that
the final conclusion is generally given first. You should begin the report by identifying your
unknown compound, by providing a structure and/or IUPAC name. Make certain you report your
unknown number!
For instance, “It was determined that unknown #58 was ethanol:
CH3CH2OH.” A major portion of the grading on this report is the correct ID of your compound;
if you do not report the unknown number, there is no way to determine the accuracy of your
identification – this will result in a significant decrease in your grade!.
Note that for the unknown from week #1, you only need to identify the functional group,
not the identity of the compound, as described above.
Description of the Unknown compound: Provide a brief description of the appearance of
the unknown, including phase, odor, color and any other simple observations that a particular to
your compound. For instance: “A sample of unknown #6 was received; the sample is a colorless
liquid with a sweet odor.”
Tests performed: Report all of the tests you performed, and the results, including those
that gave a negative result. (Remember that “negative” test results are just as important as
“positive” results!). Although it is not strictly necessary, tests are usually reported in the same
order that you performed them. Solubility test results should certainly be included!
For all tests that gave a positive result, show the reaction that occurred in the test. DO
NOT SHOW A GENERAL REACTION. Show the actual reactants and products, with full
structures. (Note that solubility tests do not have reactions)
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Spectral Analysis: The NMR and IR spectra that you received during the experiment (or
photocopies of the spectra) MUST BE INCLUDED with your report.
For H-NMR spectra, an analysis must be provided. The easiest way to do this is to draw
the structure of the unknown under the spectrum, with each unique hydrogen group labeled with a
letter, “a”, “b”, “c”, etc. Then, on the spectrum itself, each signal should be labeled with the
corresponding letter for the hydrogen group that gave that signal. For an example, see page 566
in your textbook (Organic Chemistry by L.G. Wade, 4th ed.).
The same type of analysis should be provided for C-NMR spectrum (if you received
one), with each unique carbon type labeled.
For IR spectra, label all absorbance bands on the spectrum that you can identify. This
may be done is tabular form as opposed to a verbal description of the spectrum, for instance:
Absorbance
Bond type
Broad peak, 3500 cm-1
O-H
Sharp, needle-like, 3100 cm-1 C=CH
Intense peak, 1700 cm-1
C=O
etc.
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