Ag+ NAME: NATALIE BOWSINGH PROFESSOR: Dr Martin Telting Diaz CHEM: 241 SECTION WWW DATE: 03/07/2013
Introduction: The purpose of this experiment is to determine the quantity of KI and KCI in a supplied salt mixture. Mixture of halides will be titrated with AgNO3 solution and a ph meter is use for monitoring the mV and a analytical balance is used for weight.
Materials/ Apparatus: unknown containing KCI and KI , 6ml of 0.4 M bisulfate buffer, 1.2g AgNO3, pH meter with combination electrode and Ag wire electrode, magnetic stirrer, burette, pipette and volumetric flask
Procedure: To determine the quantity of KCI and KI in an unknown by performing a potentiometric halide titration with AgNO3 as the titrant.
1. The vial with the unknown was weighed, then poured into beaker, dissolved with 20ml of water and ...view middle of the document...
This titration was repeated again.
Discussion: The technique of potentiometric measures the potential of an indicator electrode that is coupled with a reference electrode. In this technique there is no current flow between the electrodes. The measured potential then can be used to determine the analytical quantity of interest, generally the concentration in some component in the analyte solution. The potential difference that develops in the electrochemical cell is the result of the free energy change that would occur if the chemical wre to proceed until the equilibrium condition has been satisfied. Equation Nernst equation ∆ = − cell relates electrodes potential to the activities of the species involved in a given electrode. This experiment was done to quantify of each halide salt in a solid mixture of KI and KCI followed with AgNO3 solution as the titrant. The activity of Ag+ would vary during the titration in the reaction mixture and activity of Ag+ was monitored as the titration proceed using Ag/Ag+ electrode as the indicator (test) electrode. The fact that iodide is mor insoluble than chloride, when added AgNO3 to the solution containing
halide ions CI- and I-, the less soluble AgI- precipitated before AgCI. Why? The iodine is more reactive than chloride because the atomic weight is much heavier. The weaker base the better the leaving group. Therefore, iodide reacts faster with Ag+. There were two abrupt charges in the electrode potential. The iodide was consumed first then followed by the CI-. When the iodide was consumed, the electrode potential decreased. The first jump was from 223mV to -95mV at 22ml and the second was 212mV to 308mV at 48.05ml. mass calculated for both KI and KCI was 1.566g while the initial mass given in the lab was 1.20079. Evidently, this could have been human errors. While titrating, the burette was left accidently open allowing more titrant to flow than i should after the first jump. I lost about 3ml into the mixture and lost track of the mV. In the future, it’s wise to pay keen attention to gather proper data.