Chem 223 : Experiment 7
Ion – exchange and Titration Method for the Determination of
Cobalt and Nickel
1. C, Chaps. 13 (pp. 371-376), 16 (pp. 451-455).
2. H7, Chaps. 19, 23, and 25
3. S & W, Chaps. 15 (especially pp. 443-49), 17 (pp. 487-89).
4. SWH, Chaps. 18, 20 (pp. 505-518), 25 (pp. 652-653), 29 (pp. 715-716).
5. J. S. Fritz & G. H. Schenk, Jr., Quanta. Analyt. Chem., 4th ed., (pp. 582 & 621).
6. J. A. Dalziel and A. K. Slawinski,
, 367-372 (1968).
7. Bjerrum, A. S. Halonin, and L. H. Skibsted,
Acta Chem. Scand.
8. Chem 222. Truman State University
The procedure of separation of Co
in this experiment is mainly based on the lab.
“Spectrophotometric determination of cobalt and nickel” Chem. 223. UIUC
I. Purpose of the experiment
Determination of multiple components in a single unknown is frequently required. An analyst
has a choice of attempting a simultaneous determination or performing a preliminary
separation. Each approach has its advantages and drawbacks. Because few techniques are
truly specific, any simultaneous determination usually suffers from some mutual interference
between the combined components, with resulting loss of accuracy and/or precision.
Frequently, however, the resulting uncertainties are less than those introduced by the extra
sample handling required for preliminary separation. Furthermore, simultaneous
determinations are often faster, and therefore more efficient, than those relying on separations.
Generally, the choice of a preferred method must be based on the analyst's assessment of the
balance among these factors.
In this experiment, the amounts of Co(II) and Ni(II) in a mixture will be determined by two
different approaches. First of all, the Co(II) and Ni(II) will be isolated by ion exchange and
the separated components assayed. After that Co
will be complexometrically titrated using
replacement method and Ni
will be determined by gravimetric analysis.
Ion Exchange Chromatography relies on charge-charge interactions between the solutes in
your sample and the charges immobilized on the resin of your choice. Ion exchange
chromatography can be subdivided into cation exchange chromatography, in which positively
charged ions bind to a negatively charged resin; and anion exchange chromatography, in
which the binding ions are negative, and the immobilized functional group is positive. Once
the solutes are bound, the column is washed to equilibrate it in your starting buffer, which
should be of low ionic strength, then the bound molecules are eluted off using a gradient of a
second buffer which steadily increases the ionic strength of the eluent solution. Alternatively,
the pH of the eluent can be modified as to give your solues or the matrix a charge at which
they will not interact and your molecule of interest elutes from the resin. If you know the pH
you want to run at and need to decide what type of ion exchange. If it is negatively charged at