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

Table of Contents 2 Aim of the practical: 2 Introduction 2 Method: 3 Discussion 4 Different Cr (III) complexes formed under different conditions: 4Separation of complex cat-ions using ion exchange chromatography: 4Use of UV-Vis to determine 10 Dq: 5Result 5Calculation of 10Dq for [Cr(H20)6]3+ 5Estimation of the relative crystal field strengths of Cl- and H2O: 5Conclusion: 6 References: 7 Title:Separation of Complex Cat-ions of Chromium (III) by Ion Exchange ChromatographyAim of the practical: The aim of the experiment is to separate the complex cat-ions present in Chromium (III).

Ion exchange chromatography provides a way for the separation of complex and complicated cat-ions attached to Chromium (III) by replacing those complex cat-ions with ion exchange resins cat-ions.IntroductionAn ion exchange chromatographic process depends upon ionic properties which are related with the distribution of co-efficient for ion exchange resins (Fritz, Gjerde & Gjerde 2000). Separation of ions by ion exchange processes is a vital technique in chemistry. The ions to be separated are passed over the ion exchange resins and some of them become attached to the material by displacing existing complex cat-ions in the material.

The ion exchange resins which are mostly used are insoluble polymers. The relative amount of divinyl-benzene affects the physical properties and solubility of the resins..Method:1. An ion exchange column is prepared in a 50 cm3 burette half filled with de-ionized water. A small cotton wool is put at the bottom of column.2. 100 cm3 of [CrCl2 (H2O) 4] + solution is prepared by dissolving CrCl3.6H2O in 100 cm3 of aqueous HClO4 3. 5 cm3 of the [CrCl2 (H2O) 4] solution is then poured on the top of cat-ion exchange resins.4. The solution is allowed to drain the column and then HClO4 is added to the column5.

The [CrCl 2(H2O) 4] is eluted using a flow-rate of approximately 1 drop per second. 6. A portion of the elute is collected (this is of a relatively intense color).7. A flask containing 10 cm3 of the [CrCl2(H2O)4]+ solution is swirled in a water bath and 10 cm3 of water is added immediately.8. The entire solution is poured carefully on to the top of a fresh column. 9. After the solution is drained to the resin level, the column is washed with HCIO4 until the un-reacted [CrCl2 (H2O) 4] has been eluted to approximately 5 cm3 of the intensely colored fraction and the UV visible spectrum measured. 10. 10 cm3 of [CrCl2 (H2O) 4] + solution is diluted with 10 cm3 of distilled water and boiled for 5 minutes. 11. An additional 10 cm3 of water is added to the resulting solution of [Cr (H2O) 6]3+, and cooled to room temperature. 12. All of this solution is added carefully to the column and drained until the solution level reaches that of the resin. 13. The column is rinsed with HCIO4 removing any un‑treated single cat-ion and double cat-ion.

The complex [Cr (H2O)6]3+ with HClO4is then eluted 14. 5 cm3 of an intensely colored portion of the eluted [Cr (H2O) 6]3+ solution is collected and its UV visible spectrum recorded (ŠIkovec, Franko, Novič & Veber 2001).Discussion Different Cr (III) complexes formed under different conditions: Chromium (III) is the simplest ion that chromium forms in solution. Chromium (III) prefers to form octahedral complexes whose color is determined by the ligands attached to the chromium center.

It forms different complexes under different conditions.When chromium (III) reacts with alkaline, it forms green gelatinous precipitate called Chromium (III) hydroxide. [Cr (H2O) 6]3 + 3OH ==> [Cr (OH) 3(H2O) 3] + 3H2OWhen Chromium (III) ions combine with aqueous sodium carbonate, they form the green hydroxide precipitate. [Cr (H2O) 6]3+ + H2O ==> [Cr (H2O) 5(OH)] 2 + H3OWith excess sodium hydroxide or ammonia, further complex ions are formed from chromium (III) ions by ligand displacement reactions.

Cr (OH) 3 + 3OH ==> [Cr (OH) 6]3Separation of complex cat-ions using ion exchange chromatography: . Regarding the ion exchange process for Chromium (III), the ion exchange resins used is SO3H group. Aqueous solutions of the complexes trans‑[CrCl2(H2O)4] Cl, [CrCl(H2O)5]Cl2 and [Cr(H2O)6]Cl3 will be isolated in a pure state based on their different affinities for a cationic exchange resin. Use of UV-Vis to determine 10 Dq: Only a single beam of UV-VIs is used to determine 10 Dq.

They have “the ligand field splitting energy” which helps to determine this easily and quickly. This is because there is no d-d electron transition as the d orbitals are completely filled and UV-VIs bands are not observed (Pantsar-Kallio 1997). ResultAs a result, two bands are observed in the region 350 to 750 nm. This band energy is used to identify and characterize complex ions. The peak tells us that how much energy is absorbed at each wavelength of the UV. The longest wavelength band (distance between two adjacent peaks on graph) of the two has energy approximately equal to 10Dq for the complex ion.

Calculation of 10Dq for [Cr(H20)6]3+ (the energy of the band is exactly equal to 10Dq in this case):Chromium (III) cat-ion10Dq value obtained from UV-VIs spectrum (kJ mol-1)[CrCl2(H2O)4]+188.08[CrCl(H2O)5]2+195.14[Cr(H2O)6]3+206.53Estimation of the relative crystal field strengths of Cl- and H2O: The relative crystal field strength of H2O is high than Cl because Cl ligand has a weak field ligand and determines a smaller value of 10 Dq while [Cr (H2O) 6]3+ has the highest 10Dq because there is no Cl ligand in it only H2O is present which is a strong field ligand and determines a higher value of 10 Dq.

(Place original print-out of your result here) Conclusion: From the above experiment we may conclude that in the ion exchange method of Chromium (III), [Cr(H2O)6]3+ has the highest value of 10 Dq, that is, 206.53 due to the absence of weak field strength of Cl while [CrCl(H2O)5]2+ and [CrCl2(H2O)4]+ has low value due to the presence of Cl ligands. References:Top of FormŠIKOVEC, M., FRANKO, M.

, NOVIČ, M., & VEBER, M. (2001). Effect of organic solvents in the on-line thermal lens spectrometric detection of chromium(III) and chromium(VI) after ion chromatographic separation. Journal of Chromatography. A, 119-125.Top of FormFRITZ, J. S., GJERDE, D. T., & GJERDE, D. T. (2000). Ion chromatography. Weinheim, Wiley-VCH.Bottom of FormTop of FormPANTSAR-KALLIO, M. (1997). Development of speciation methods for arsenic, chromium, halogenides and oxyhalogens by ion chromatography-inductively coupled plasma mass spectrometry.

Helsinki, Päijät-Paino Oy.Bottom of FormBottom of FormTop of Form