Chemistry 7B
Name ________________________________
SOLUBILITY UNKNOWNS, ELEMENTAL ANALYSIS, AND CHEMICAL
CLASSIFICATION TESTS REPORT FORM
Solubility Unknowns
For each of four unknowns, list one of the following eight solubility classifications:
low MW neutral
low MW acid
low MW base
strong acid
weak acid
base
neutral
inert
Unknown
Classification
Elemental Analysis (see attached instructions)
A. Presence of N, S, X
Known Negative
Known Positive
Known Negative
Known Positive
Compound Tested:
Nitrogen
Test
Observations:
Compound Tested:
Sulfur
Test
Observations:
(A) Known (-)
Compound Tested:
Halogen
Test
Observations:
(B) Known Cl
(C) Known Br
(D) Known I
B. Halogen Differentiation Tests (Chlorine Oxidation Test)
Compound Tested:
No Halogen
A
Observations:
Compound Tested:
Chlorine
B
Observations:
Compound Tested:
Bromine
C
Observations:
Compound Tested:
Iodine
D
Observations:
Chemical Classification Tests
Carry out the following chemical classification tests on appropriate known compounds and your unknown. The
procedures for each are in the lab text or the supplemental handout. This is not a complete list of the tests
which you may need to use for your unknowns, but is meant to give you practice with most of the more
important ones.
Classification Test
Tests For
Known (-) Used
Known (+) Used
Bromine / methylene
chloride
Isolated double
bonds
toluene
2-pentene
Silver
Nitrate / Ethanol
2,4-Dinitrophenylhydrazine
Chromic Acid
Tollens’ Test
Observations
orange color disappeared
immediately upon addition to
2-pentene, but not toluene
Classification Test
Tests For
Known (-) Used
Known (+) Used
Observations
Ferric Chloride
Bromine Water
Nitrous Acid
Lucas Test
Ferric Hydroximate
Aluminum Chloride
/ Chloroform
For further practice, you may wish to review and carry out other chemical classification tests on your own.
These tests could include but are not limited to:
1. Ethanolic sodium iodide on various organic halides.
2. Ethanolic silver nitrate on RCO2H.
3. Potassium permanganate (Baeyer test) on an alkene, an alkane, toluene, and acetone.
4. Iodoform test on acetone, 2-butanol, 1-butanol.
Chemistry 7B
PROCEDURE FOR ELEMENTAL ANALYSIS (N, S, and X)
Sodium Fusion
To test for nitrogen, sulfur or halogens in your organic unknown it is first necessary to completely
destroy the molecule by sodium fusion, releasing these elements as NaCN, Na2S, and NaX. The
resulting aqueous solution can be tested for these ionic species.
There are a number of ways to perform a sodium fusion, but the following method works well. First
obtain a test tube containing a small piece of sodium metal. Using a test tube clamp, hold this test
tube over a Bunsen burner flame just until the sodium melts. Do not overheat because you will
destroy the sodium sample. Immediately after it melts remove from the flame, hold it over a 50 mL
beaker containing 5 mL of distilled water and quickly add a small amount of your sample (solid or
liquid) to the melted sodium. Make sure you add your sample so that it makes contact with the
sodium, and not down the side of the test tube. The reaction with the sodium can result in a flash
and may even break the test tube (which is why you perform over a beaker). If nothing is observed it
you may have to repeat the procedure.
If your test tube breaks, try and scrape all remaining residue from the test tube into the beaker
containing 5 mL of distilled water. If your test tube did not break, add about 10 drops of methanol to
the tube and scrape the inside of the test tube with a spatula to loosen it from the sides of the test
tube. Do this over the beaker because occasionally test tubes will crack during the sodium fusion, but
do not appear broken. Pour all of the methanol and residue from the test tube into the 5 mL of
water. If residue remains in the test tube you may add a small amount of distilled water to the test
tube to rinse it out into the beaker. To prevent unnecessarily dilution the best method is to pipet
water from the beaker back into the test tube to rinse. The aqueous solution in the beaker is the
stock solution you will test for NaCN, Na2S, and NaX. You may store this solution in a sealed,
labelled flask in your drawer for later analysis.
Tests for N, S, and X
The first time you do these tests, you should always prepare (by sodium fusion) stock solutions that
you know contain these elements and solutions that you know do not contain these elements. This is
so you can see how both a positive and negative test appear.
Nitrogen (in the form of CN-)
Perform the ferrous sulfate test as described in the lab text. An additional test known as the pnitrobenzaldehyde in DMSO test (found in handout), can be done as a conformation. This test is also
sensitive to sulfur (see below).
Sulfur (in the form of Na2S)
Perform the sodium nitroprusside test as described in the handout.
Halogens (in the form of NaX)
Perform the silver nitrate test as described in the lab text to determine if a halogen is present. If a
halogen is present, a further test using chlorine water should be done to differentiate which halogen
is present. This is described in the lab text under the heading Differentiation of Chlorine, Bromine
and Iodide (p. 464 in Pavia 2nd edition).
Samples to prepare for elemental analysis (first lab)
Stock solution 1: Contains both nitrogen and sulfur (use thiourea)
Stock solution 2: Does not contain nitrogen, sulfur, or halogen (use toluene)
Stock solution 3: Contains chlorine
Stock solution 4: Contains bromine
Stock solution 5: Contains iodine
Nitrogen test:
Do two tests side by side using stock solutions 1 and 2
Sulfur test:
Do two tests side by side using stock solutions 1 and 2
Halide test:
Do four silver nitrate tests side by side using stock solutions 2, 3, 4 and 5.
Do four differentiation tests using these same stock solutions.