Dates of Experiment: 10/14/08 through 10/30/08
Date of Report: 11/7/08
In this experiment, the zinc and nickel contents of unknowns were tested using two methods. In the first method, nickel and zinc were separated through ion-exchange chromatography and analyzed through chelometric titration. In the second method, the unknown was analyzed through the atomic absorption spectroscopy (AAS) of the mixture.
In and ion-exchange column, the ions are separated due to their tendencies to interact with the fixed phase of the column. In this case, the anion-exchange resin is that fixed phase. Nickel passed through the column unhindered and therefore first. Zinc formed chlorozincate anions that reacted with the resin. It could not pass through the column until a neutral aqueous solution was run through. The elements were determined quantitatively by titration with ethylenediaminetetraacetic acid (EDTA). This method is valued as a good estimate and is used widely because of its use of common lab equipment. Only a single column was run for each metal in the interest of time. To acquire a meaning for the effect that the method has on the outcome, one should split the sample into replicates before the column. However, this may lower the accuracy, reduce the precision, and increase the time of the analysis.
In AAS, ions are distinguished due to the wavelength of light emitted when atomized ions are passed through a flame. Each element has a characteristic wavelength of light emitted. The instrument is calibrated using standard solutions prior to passing samples through. The results are interpreted using a calibration curve. This method is valued due to its efficient speed, ease of use, high selectivity, accuracy, and precision. A...