Separation of Complex Cations of Chromium(III) by Ion Exchange Essay

Separation of Complex Cations of Chromium(III) by Ion Exchange Chromatography - Essay Example Water soluble compounds of Chromium III do not occur naturally and are unstable in the environment (Nriagu & Nieboer, 1988 p68). Different oxides of chromium oxide are also used as pigments. Cation exchange chromatography can be used to separate different chromium III complexes into their pure forms. The most common complexes are chromium III and IV which exist at different ionisation states. Chromium III is a cation and IV is an anion. Chromium VI is toxic to humans (Vincent, 2011 p101). The separation of these complexes is based on their different ionisation states which are the principles behind ion exchange chromatography. The use of UV-Vis as analytical tools is essential in determining the value of 10q of elements. The coupled use of these diagrams and spectroscopic information enables someone to correctly calculate the electromagnetic absorption of metal compounds and how the crystal fields split energy or 10Dq (Kettle, 2008 p69). 3. Chromium solutions are then prepared that will be used throughout the experiment. At this stage, progress should immediately be made towards separation of trans-‑[CrCl2(H2O)4]+, [CrCl(H2O)5]2+ and [Cr(H2O)6]3+ after which their spectrums are measured between wavelengths 350 nm and 750 nm immediately after their collection (Beran, 2010 p200). 4. The final step involves the estimation of relative crystal field strength for Cl- and H2O. Two bands are observed in the region of 350nm and 750nm with the longest wavelength band having energy equal to 10Dq or the octahedral Crystal field splitting energy for the complex ion. Chromium III compounds have bands that are easy to interpret and they exist either in an excited state which has higher energy than the ground state which has less energy but more stable. The values of 10Dq are shown to decrease with the increasing charge of a neighbouring anion and the decreasing number of coordinating anions (Crabtree, 2011