jagomart
digital resources
picture1_Thermal Analysis Pdf 89089 | Chapter 22 Coulometry


 154x       Filetype PDF       File size 0.35 MB       Source: sites.usm.edu


File: Thermal Analysis Pdf 89089 | Chapter 22 Coulometry
chapter 22 bulk electrolysis electrogravimetry and coulometry definition z bulk electrolysis deals with methods that involve electrolysis producing a quantitative change in oxidation state 2 z example in a mixture ...

icon picture PDF Filetype PDF | Posted on 15 Sep 2022 | 3 years ago
Partial capture of text on file.
                                 Chapter 22 
                             Bulk Electrolysis:
                   Electrogravimetry and Coulometry
                  Definition
                  z Bulk Electrolysis deals with methods that 
                    involve electrolysis producing a 
                    quantitative change in oxidation state
                                                        2+
                  z Example: In a mixture solution of Zn   and 
                    Cu2+, convert all Cu2+ to Cu metal and leave 
                       2+
                    Zn in the solution. 
                    ÆHold the working electrode (e.g. Cu) 
                    potential at a certain value (positive than 
                    that for Zn reduction)
                              Cu2+(aq) + 2e Æ Cu(s)
                  Features of Bulk Electrolysis Cells
                  z Big working and counter electrodes—
                    ~100 times larger than normal electrodes 
                    (e.g., in CV)
                  z Large cell currents (mA vs μA-nA)
                  z Stirring Solution (mainly convection)
                  z working and counter electrode placed in 
                    two separated cell compartments 
                    (avoiding by-products produced at the 
                    counter electrode)
                                                                                                                                    1
                                An example of bulk 
                                electrolysis cell produced 
                                by Bioanalytical System, 
                                Inc.
                Classification
                z Three Types
                  z Electrogravimetric analysis
                            M2+ + ne Æ M(s)
                    Metal is electrolytically deposited onto a inert 
                    electrode (e.g., Pt)—the increase in mass of the 
                    electrodes gives the concentration or amount of 
                    the metal ion in the solution
                  z Constant potential coulometry
                  z Constant current coulometry
                Effect of Current on Cell 
                Potential 
                IE= / (ROhm's Law)
                I −current (Amperes, A)--flow of positive charge.
                E−potential (Voltage) (Volts,V)
                R−resistance (ohms,Ω)
                Direct current (dc)--one direction current
                Alternating current (ac)--current reverses periodically
                                                                                                                  2
                              OhmicPotential; IR Drop
                                                           E            (-) = E        (-) – IR(+)
                                                             applied               cell
                                                          -2+
                                 (A)Ag|AgCl(s), Cl (0.200 M),Cd (0.00500 M)|Cd(C)
                              How to reduce the IR drop?
                              zAlways use inert supporting 
                                 electrolyte (0.1 ~ 1.0 M 
                                 concentration);
                              zReduce the electrochemical cell 
                                 current (using small electrode);
                              zUse three-electrode system;
                              zCompensation 
                              Polarization Effects
                             z Polarization is the departure of the electrode 
                                  potential from its theoretical Nernst equation 
                                  value on the passage of current.
                             z Factors that influence polarization:
                             (a) Electrode size, shape, and composition;
                             (b) Composition of the electrolyte solution;
                             (c)  Temperature of the stirring rate;
                             (d) Current level; and
                             (e) Physical state of species involved in the cell 
                                  reaction.
                                                                                                                                                                                                                          3
                              Overpotential (Overvoltage), η
                           z Overpotential (overvoltage) develops as a result 
                               of electrode polarization:
                               (1) concentration polarization - mass transport 
                               to/from electrode limited
                               (2) Kinetic polarization - rate of redox reaction at 
                               electrode
                           z Overpotential means must apply greater 
                               potential before redox chemistry occurs
                                   η =−EE
                                                 current             reverible/equilibrium
                                         Reversible E                            Reversible E
                                                                     i         η              η
                             i          η            η
                                            E                                        E
                                     Galvanic Cell                          Electrolytic Cell
                             Due to overpotentials, for a galvanic cell, a cell potential is always 
                             smaller than that calculated from the reversible potential; for a 
                             electrolytic cell, the applied potential is always larger than that 
                             calculated from the reversible potential.
                              Mass transfer to/from 
                              electrode
                              z Mass transfer is the movement of 
                                   material (ions, molecules etc.) from one 
                                   location to another (e.g, from bulk to 
                                   electrode surface).
                              (a) Diffusion—results from concentration 
                                   gradient;
                              (b) Migration—arises from potential gradient;
                              (c)  Convection—results from stirring, 
                                   vibration, or temperature gradient.
                                                                                                                                                                                                                          4
The words contained in this file might help you see if this file matches what you are looking for:

...Chapter bulk electrolysis electrogravimetry and coulometry definition z deals with methods that involve producing a quantitative change in oxidation state example mixture solution of zn cu convert all to metal leave the hold working electrode e g potential at certain value positive than for reduction aq s features cells big counter electrodes times larger normal cv large cell currents ma vs na stirring mainly convection placed two separated compartments avoiding by products produced an bioanalytical system inc classification three types electrogravimetric analysis m ne is electrolytically deposited onto inert pt increase mass gives concentration or amount ion constant current effect on ie rohm law i amperes flow charge voltage volts v r resistance ohms direct dc one direction alternating ac reverses periodically ohmicpotential ir drop applied ag agcl cl cd c how reduce zalways use supporting electrolyte zreduce electrochemical using small zuse zcompensation polarization effects departu...

no reviews yet
Please Login to review.