PENGARUH LIGAN DAN PH 2- PADA TITRASI REDOKS FE2+ - CR2O7

• Main Author: Amelia, Winda
• Format: Theses
• Language: Indonesia
• Subjects: Kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/51860
• Institution: Institut Teknologi Bandung

The redox reaction of Fe2+ - Cr2O72- is an interesting redox system to be studied. Aside from its application for analysis purposes, redox reaction also widely used for industrial waste treatments.. The Fe2+ - Cr2O72- redox reaction can only occure in an acidic condition due to redox potential modification by the pH of the solution. The spontanity of this reaction is pH dependent, which only occure in lower pH in the presence of hydrogen ion. Therefore, further research is needed to improve the spontaneous reaction of Fe2+ - Cr2O72- redox which is influenced by pH. One effort to increase the spontaneity of a redox reaction can be done by the addition of certain ligands. The presence of a suitable ligand can modify the reduction potential of the metal ion from its free state so that the redox reaction can take place. In this research, the EDTA and SCN- ligands are used for the Fe2+ - Cr2O72- redox system because it forms a more stable complex with Fe(III) compared to Fe(II) allowing the reaction to shift toward the product. The pH range of the solution for the redox titration of Fe2+ - Cr2O72- in the presence of a ligand must be considered because of its deposition and influences the stability of the complex. However, the situation is not simple because in the solution there are complex combinations such as MHiL or MOHjLi. Based on this problem, further research is needed regarding the effect of ligands and pH on the redox titration of Fe2+ - Cr2O72-. This study uses a potentiometric titration method involving local Ag/AgCl electrodes as a reference electrode and platinum wire as a working electrode. The characterization of local Ag/AgCl electrodes was carried out by two methods namely voltammetry and potentiometry. Local Ag/AgCl electrodes are good enough to be used in measurements known from the results of paired T- test with tcount (1,359) < ttable (2,78) and Nernst factor of 51,9 mV / decade at 25 °C. Redox Fe2+ - Cr2O72- titration can only be done up to pH 2. Decreasing the concentration of sulfuric acid in the redox titration of Fe2+ - Cr2O72- decreases the sharpness of the titration curve at the point equivalent area. Furthermore, the redox titration of Fe2+ - Cr2O72- with the addition of EDTA and SCN- ligands was carried out at that pH. Adding an excess of EDTA ligand to the total Fe(II) ion results in a very sharp titration curve. However, there was a slight shift in the volume of the equivalent point earlier than theoretical calculations as a result there is a small fraction of Fe(II) species which is not fully complexed. This condition can occur because the pH of the solution affects the stability of the [Fe-EDTA]-/[Fe-EDTA]2- complex. This can be proven through the E-pH diagram of the Fe(III)/Fe(II) system in the presence of an EDTA ligand experimentally that the redox potential is not constant with changes in pH below 3. The redox titration curve Fe2+ - Cr2O72- with the addition of EDTA and SCN- ligands at pH 2 was compared to determine the effectiveness of the ligands against the redox system. EDTA ligands are effective enough to increase the sharpness of the Fe2+ - Cr2O72- redox titration curve at pH 2 compared to the addition of SCN- ligands. However, EDTA ligands are less effective in determining the equivalent point volume because there is a shift from theoretical calculations. The results of the study of the influence of ligands and pH on the redox titration of Fe2+ - Cr2O72- were subsequently used as a reference for the development of learning modules on electrochemical materials at SMA Mutiara Bunda Bandung class XI. The module test results obtained by the percentage of responses and learning activities of students respectively 78,60 and 83,30%. The percentage of these results shows that the development of learning modules can increase interest and learning activities for electrochemical subject.