WOLFRAM|DEMONSTRATIONS PROJECT

Classical Qualitative Inorganic Analysis

​
general scheme
cations
2+
Pb
2+
Hg
+
Ag
2+
Ni
2+
Co
SuperscriptBox[\(Fe\), \(2 + \(\(/\)\(3\)\) + \)]​
2+
Hg
2
2+
Cu
3+
Bi
2+
Cd
SuperscriptBox[\(As\), \(3 + \(\(/\)\(5\)\) + \)]​
SuperscriptBox[\(Sb\), \(3 + \(\(/\)\(5\)\) + \)]​
SuperscriptBox[\(Sn\), \(2 + \(\(/\)\(4\)\) + \)]​
3+
Al
3+
Cr
2+
Mn
2+
Zn
2+
Ca
2+
Sr
2+
Ba
2+
Mg
This Demonstration shows the steps in the qualitative analysis of an unknown mixture of cations in an aqueous solution, without the formation of insoluble precipitates. This is a classic procedure, long since superseded by spectroscopic methods, but possibly still useful for teaching chemical laboratory techniques. The following anions are assumed to have been already eliminated:
-
CN
,
3-

III
Fe
(CN)
6

,
4-

II
Fe
(CN)
6

and
-
CNS
. Other interfering anions are eliminated in the course of the procedures.
The analysis in this Demonstration is based upon separating the different cations into groups, following selective precipitations due to the common ion effect, which, in turn, is pH related. Each precipitate must be washed at each separation, according to the standard procedures of analytical chemistry. Our choice is to represent the solution path through the vertical flow line, while the precipitates are represented by horizontal flow arrows. The bifurcations show the division of the solution into different portions. A missing cation does not guarantee the absence of precipitate because of several possible problems (e.g. incomplete precipitation). To highlight this, the precipitate that should not be there but could show up is written in red.
Using the drop-down menu, it is possible to select the general scheme or a scheme limited to specific groups. When "general scheme" is selected, by checking the relevant checkbox it is possible to choose the cations and display the path followed in the analysis. The path should almost always end up through a special reaction uniquely identifying the cation; such unique identification is possible because of cation separation. The VIB Group procedure is not taken into consideration, as in standard lab practice these cations are more easily identified by means of a flame test.