CHE 450G: Practical Inorganic Chemistry

U of KY Dept of Chemistry

Ion-Exchange Separation of the Oxidation States of Vanadium

Introduction and Background

The experimental procedure can be found in Szafran, Experiment #28 (on reserve).

There is one addition to the experiment. We will obtain an ESR spectrum of one of the blue species that you separate by chromatography. An appropriate introduction to ESR spectroscopy (also called EPR and EMR) can be found in the Required Reading for this experiment.

Please note the other changes, additions and tips regarding the experimental procedure .

Required Reading

Read the following BEFORE performing this experiment:
1. The background reading suggested in Szafran's introduction
2. The instructions for using the Shimadzu UV-VIS spectrometer.

Read the following BEFORE obtaining your ESR spectrum:
1. Drago, Sections 9.1, 9.3, 9.4 and 9.10 (on Reserve).

Optional but useful information (for motivated students):
1. Cotton and Wilkinson, Sections 18-B-3, 18-B-4 and 18-B-5 (Chemistry of V-oxo species).

2. Parish et. al., Chapter 5 (ESR, on Reserve)

Synthesis and Characterization

Equipment and Chemicals required

• Ammonium metavanadate (chemical shelves).
• Mercury(II) chloride (chemical shelves).
• Zinc dust (chemical shelves).
• Hydrochloric and nitric acid (acid storage; you must make your own dilute solutions).
• Dowex AG50W-X2 cation exchange resin, 100-200 mesh (chemical shelves).
• A buret for use as chromatographic column + a buret clamp (found in cabinet below the distilled water container).
• 0.001 M KMnO₄ solution (pre-made, chemical shelves).
• Beakers, flasks, spatulas etc. Test tubes can be found in the common equipment cabinet.
• A clean ESR tube (obtain from TA).
• UV-VIS cells (found next to the Shimadzu).

General Considerations

• CAUTION: The ammonium metavanadate, mercury(II) chloride and zinc amalgam are harmful or toxic if swallowed, inhaled or absorbed through the skin. Use proper protective measures.

• The zinc amalgam waste should go in a special solid mercury waste container. Consult your instructor if you can not find the proper container. Be certain to scale down your amalgam preparation according to procedure below.
• Students in prior years have reported success using the Alternate Method instead of the Second Separation method to obtain the V(II) and V(III) species. Use whichever one you want (or both).

Procedure

Follow Szafran's procedure, but:

• A convenient way of breaking this experiment into 2 days is to stop after the first separation. Obtain the UV-VIS data on your two fractions and the ESR spectrum of your blue fraction and then complete the experiment on Day 2.

• Scale down the amount of amalgam to 40 mg of HgCl₂. To avoid measuring ridiculously small volumes of nitric acid you can make a stock solution of dilute nitric acid and use that to prepare your amalgam.

• Dispose of your amalgam when you are completed (see above).

• Just to clear be clear: take UV-VIS spectra of your four different ions (yellow, green, violet and blue) on the Shimadzu using your eluant as a blank. You can do the KMnO₄ test in situ by then adding the KMnO₄ solution to the cuvette, noting any decolorization and then retaking the spectrum.

• Take some of your blue solution and bubble a stream of nitrogen through it for a minute or two to remove dissolved oxygen. Pipette this solution into your ESR tube and then contact your instructor about obtaining the ESR spectrum.

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This document and associated figures are copyright 1996-2000 by Rob Toreki. All rights reserved.