Spectrophotometric Analysis Of Copper Iodide

Experiment 2 Preparation and Spectrophotometric Analysis Of Copper (I) Iodide (CuI)

Abstract

The aim of the experiment was to obtain pure Copper (I) Iodide (CuI) and to determine the mass percentage of copper in the purified CuI sample .Crude CuI was obtained by redox reaction of Copper Sulphate pentahydrate (CuSO4.5H¬¬2O) and Potassium Iodide. The crude CuI was further purified to obtain pure CuI. Standard solutions with known concentrations of Cu2+ ions, ranging from 0 to 0.0032g/L was prepared and the absorbance values were obtained via UV-VIS spectroscopy. A graph of absorbance value against the concentration of Cu2+ was plotted to measure the concentration of Cu2+ in the pure CuI. It was found through UV-vis spectroscopy, the experimental

The solution was warmed to 65oC with constant stirring on the magnetic stirrer till the solid was completely dissolved. Stirring was stopped and 0.4g of charcoal was then added to the solution. After which the solution was transferred to a Buchner funnel with a moist filter paper and the clear filtrate was collected via suction filtration. The residue was washed with warm solution of 10.035g of KI and 15ml of deionized water. 200ml of water was then added to the filtrate in a 500ml beaker with constant stirring. White solid was formed in the process of addition and the solution was then left undisturbed in an ice bath for 10minutes. Once most of the solids had settled at the base of the beaker, the solution was decanted. 10ml of ethanol was added to the remaining suspension and was transferred in a clean centrifuge and centrifuged for 2minutes at 6000rpm. After the first centrifugation, the supernatant was discarded and the residue was washed by adding 14ml of ethanol. The subsequent centrifugation was repeated twice, only this time using 8ml of diethyl ether instead of ethanol. After centrifugation, the purified CuI was left to dry in the film hood. The mass of the purified CUI was then weighed and

This is more than the theoretical mass percentage of Cu in the purified sample. The concentration of Cu2+ was retrieved from the graph above. This discrepancy could be due to impurities existing in the compound which could have absorbed the UV-vis light at wave length 600nm too which led to a higher absorbance reading.

The percentage yield of crude CuI obtained was more than 100%. This could be due to the presence of impurities such as I2, this is seen by the tan colour of the compound which is due to the presence of Iodine instead of obtaining a white compound as a result of Na2S2O3 not removing the Iodine completely or due to the slow decomposition of CuI. Thus leading to additional weight therefore the percentage yield crude CuI was 159%.

Water was not entirely removed throughout the drying process hence leading to an increase in mass resulting in a claylike compound. Water could have also remained in the centrifuge tube and was not removed at it was cetrifugated to the bottom of the centrifuge tube. Thus giving rise to the mass of CuI obtained. This could have been prevented by thoroughly mixing the solid compounds with ethanol after centrifugation to ensure that the water is dispersed and reacted with the ethanol. A better way to eliminate water is by high frequency sonar to disperse the residue better after each centrifugation to ensure dispersal of the residue at the bottom of the centrifuge