Experiment 5- Page 1
Semimicro Qualitative Analysis
A complete chemical analysis of a sample focuses first on what is in the sample (a systematic study called
Once the chemist knows which substances are present, then a quantitative analysis is performed
to determine how much of each substance is present.
Many times the chemist has only a limited amount of sample with which to work and analytical procedures must
be done on a semimicro or micro scale.
Instrumental techniques can often be used in such cases.
Techniques based on
wet chemistry, however, are often simpler and can be used to quickly analyze a sample (at least for semiquantitative
In this experiment, you will investigate a mixture of ten common metal ions.
This is best accomplished by
studying them first individually to determine typical reactions for each ion.
In the second part of the experiment, you
will be given an
sample that may contain from one to ten of these metal ions.
The goal will be to follow a
procedure to separate them first into several groups, each of which contains ions exhibiting a common chemical
property that is the basis of the separation based on solubility.
Specific tests will then be run to determine individual
components of the mixture.
For comparison purposes, you will run all
tests in Part II of this experiment on both your
sample and a
"control" sample (sometimes colloquially called a '
This "control" sample will contain all of the ions in
By comparing the results from you
sample to the definitive results from your "control" (or '
sample, you will be able to determine whether a particular ion is present in your
(i.e., if your
behaves exactly the same way as your "control", then the ion in question is present in your
If, on the other
hand, you obtain a positive result from your "control" but nothing happens with your
, then that ion is not
present in your
For the best comparison, it is strongly advisable that you run all tests on both your
The theory behind the separation and identification of ions in the qualitative analysis scheme presented in this
experiment follows a series of important concepts that you learned in lecture.
Ionic equilibria, complex ion formation,
solubility products and oxidation reduction reactions will all enter into the scheme of separation.
Make certain that you
understand the chemistry behind the reactions involved.
Remember that you will use the concepts of
, ion product
H, weak acid-weak base complexation in this experiment.
Many separations will involve the formation of
Although no species is totally soluble or insoluble, generalized solubility rules can be made for
aqueous solutions, which include:
All salts containing the chloride ion, Cl
, bromide ion, Br