Identifying an Unknown Compound by Solubility, Functional
Group Tests and Spectral Analysis
This handout is a supplement to Signature Lab Series ANAL 0727 and contains material adapted from
Signature Lab Series ANAL 0727 and 0728, Cengage Learning. This lab contains material copywritten by
Cengage Learning and has been reproduced only to adapt the lab to experimental needs. This
supplement should not be used without the purchased lab manual, which contains the above
experiments.
Purpose Of The Experiment:
Identifying an unknown organic compound through a three-step process involving selective solubility
tests, selective functional group tests and spectral analysis.
Background Required:
You should be familiar with techniques for weighing, measuring by volume, and mixing in a test tube, as
well as analysis of 1H NMR and 13C NMR spectra.
Background Information:
Organic qualitative analysis is an exercise in spectroscopy. Nuclear magnetic resonance
spectroscopy and infrared spectroscopy are the major spectroscopic techniques used by organic
chemists. However, much insight can be gained from using simple qualitative tests to determine the
identity of unknowns. Structures of unknown compounds can be determined by comparing physical
properties, performing functional group tests, and checking melting points of derivatives against those of
known compounds reported in the literature. Solubility properties and chemical reactivity become
apparent during these qualitative tests.
Spectroscopy has been discussed extensively in the lecture portion of this course.
Organic qualitative analysis involves four types of tests.
1. Measurement of physical properties includes determining refractive index, boiling points, melting
points, and density.
2. Solubility tests can suggest the size and polarity of an unknown compound and the presence of basic
or acidic functional groups. A compound’s solubility in aqueous acid or base involves ionization of the
compound and, therefore, a chemical reaction. The salts produced are water-soluble.
3. Chemical tests transform an unknown into a different compound with an accompanying change in
appearance. These tests are often called classification tests because they identify the possible
functional groups present.
4. Formation of a solid derivative is a critical step in identifying an unknown. Many compounds have
similar physical properties and give similar results in qualitative tests. However, an unknown can undergo
reaction to form another compound called a derivative. The melting point of the purified derivative allows
identification of the unknown.
In this lab we will focus on using Solubility Tests, Chemical Tests and Spectra Analysis to identify two
unknown compounds.
Overview:
In this experiment, you will combine both spectroscopy and qualitative tests to identify an
unknown organic compound. For this experiment, the possible categories of the unknown are alkane,
alkene, alkyl halide, alcohol, phenol, amine, aldehyde, ketone, and carboxylic acid. Each compound will
