Experiment 8: Quantitative Determination of Copper Concentration in Aqueous Solution by Iodometric Titration Results and Discussion
Oxidation-reduction titration is a kind of volumetric analysis where the titrant used undergoes a redox reaction with the analyte. In this experiment, the oxidation of iodide (I-) to produce iodine (I2) is taken into consideration. The use of this concept in a redox titration is called iodometry. Iodimetry, on the other hand, deals with the reduction of I2 into I-. Between these two methods, iodometry is more popular because it is more efficient to conduct due to the presence of more oxidizing agents strong enough to react with the iodide. The copper concentration of an unknown copper sample was determined using iodometric titration.
The first part of the experiment involved the preparation of the working standard Cu(II) solution of specific concentration from CuSO4•5H2O. A standard sodium thiosulfate (Na2S2O3) solution was also prepared to serve as the titrant for the analysis. Proper handling should be administered for this solution since it decomposes into its component ions when it is exposed to acids, light, and bacteria. Sodium carbonate was added to the solution to act as a preservative. Boiled distilled water was also used in dissolving the crystals to remove bacteria that may eat on sulfur. Starch indicator was also prepared using warm distilled water to detect the endpoint in the titration. Toluene may also be used as an indicator. The disappearance of the pink organic layer signals the depletion of iodide at the endpoint.
For the standardization of Na2S2O3, samples of the working standard Cu(II) solution were transferred to Erlenmeyer flasks, adding a few drops of NH4OH solution until a light blue precipitate of Cu(OH)2 is formed. The formed precipitate was then dissolved with glacial HOAc. Solid potassium iodide (KI) was added to the solution and swirled to complete the reaction. To lessen...