Ion-Exchange Separation and Spectrophotometric Determination of Nickel and Cobalt By Doan-Phuong Dao

Background information This experiment had two major steps: 1)Separation of Ni and Co in the unknown sample by using an ion-exchange chromatography column with a strong base anion exchanger 2) Determination of the concentrations of Ni and Co in the unknown sample by using standard spectrophotometric procedures

Ion exchange chromatography In ion-exchange chromatography, retention is based on the attraction between solute ions and the charged sites bound to the stationary phase. In anion exchangers, positive charged groups on the stationary phase attract solute anions Cation exchangers contain covalently bound, negatively charged sites that attract solute cations This experiment used a strong base anion exchanger

In solution containing a large concentration of hydrochloric acid, Co was converted into complex anions (chlorides) CoCl4 2-, and was adsorbed by an anion resin. Ni was not converted into complex anions so that it was not adsorbed by such a resin. The separation of Nickel from Cobalt was easily effected. The cobalt is removed by washing the resin with 1M HCl.

After separating from the mixture, Nickel was oxidized with bromine in ammonia solution and then treated with dimethylglyoxime. A wine-red or brown complex is formed. Cobalt was determined by conversion of the metal to the blue complex cobalt thiocyanate, Co(CNS)42-. 95% ethanol solution was used because both complexes were somewhat dissociated in water The concentrations of Ni and Co were determined by measuring the absorbance at 455 nm (for Ni), and at 625 nm (for Co) with a spectrophotometer.

The graphs of concentration vs The graphs of concentration vs. absorbance of Ni and Co standard solution were plotted to determine the line equations. From the line equations , the absorbance of the Ni and Co in the unknown were plugged in to calculate the concentration of each metal in the sample

Question What is required when it comes to separating Nickel and Cobalt in the column?

Answer Need 9M HCl to bind to Cobalt and release Nickel Need 1M HCl to release the Cobalt from the column.