Chapter 23 l.jpg
This presentation is the property of its rightful owner.
Sponsored Links
1 / 23

Chapter 23 PowerPoint PPT Presentation


  • 260 Views
  • Updated On :
  • Presentation posted in: General

Chapter 23. Potentiometry. Reference Electrodes.

Download Presentation

Chapter 23

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Chapter 23 l.jpg

Chapter 23

Potentiometry


Reference electrodes l.jpg

Reference Electrodes

A reference is an electrode that has the half-cell potential known, constant, and completely insensitive to the composition of the solution under study. In conjunction with this reference is the indicator or working electrode, whose response depends upon the analyte concentration.


Reference electrodes3 l.jpg

Reference Electrodes

Ideal Reference Electrode:

  • Is reversible and obeys the Nernst equation

  • Exhibits a potential that is constant with time

  • Returns to its original potential after being subjected to small currents

  • Exhibits little hysteresis with temperature cycling


Reference electrodes4 l.jpg

Reference Electrodes


Reference electrodes5 l.jpg

Reference Electrodes

Calomel Electrodes:


Reference electrodes6 l.jpg

Reference Electrodes

Silver/Silver Chloride Electrodes:


Metallic indicator electrodes l.jpg

Metallic Indicator Electrodes

There are four types of metallic indicator electrodes:

  • Electrodes of the first kind.

  • Electrodes of the second kind.

  • Electrodes of the third kind.

  • Redox electrodes.


Metallic indicator electrodes8 l.jpg

Metallic Indicator Electrodes


Membrane indicator electrodes l.jpg

Membrane Indicator Electrodes

Properties:

  • Minimal solubility. A necessary property of an ion-selective medium is that its solubility in analyte solutions approaches zero.

  • Electrical conductivity. A membrane must exhibit some electrical conductivity, albeit small. Generally, this conduction takes the form of migration of singly charged ions within the membrane.

  • Selective reactivity with the analyte. A membrane or some species contained within the membrane matrix must be capable of selectively binding the analyte ion. Three types of binding:

    Ion-exchange

    Crystallization

    Complexation


Membrane indicator electrodes10 l.jpg

Membrane Indicator Electrodes

Glass Electrodes:


Membrane indicator electrodes11 l.jpg

Membrane Indicator Electrodes

Glass Electrodes: Potential

  • The boundary potential.

  • The potential of the internal Ag/AgCl reference electrode.

  • A small asymmetry potential.


Membrane indicator electrodes12 l.jpg

Membrane Indicator Electrodes

  • Alkaline Error

  • Selectivity Coefficients

  • Acid Error


Membrane indicator electrodes13 l.jpg

Membrane Indicator Electrodes

Crystalline Membrane Electrodes:


Membrane indicator electrodes14 l.jpg

Membrane Indicator Electrodes

Fluoride Electrode:


Membrane indicator electrodes15 l.jpg

Membrane Indicator Electrodes

Liquid Membrane Electrodes:

  • Cation exchangers

  • Anion exchangers

  • Neutral macrocyclic compounds, which selectively complex certain cations


Membrane indicator electrodes16 l.jpg

Membrane Indicator Electrodes


Ion selective field effect transistors isfets l.jpg

Ion-Selective Field-Effect Transistors (ISFETs)


Molecular selective electrode systems l.jpg

Molecular-Selective Electrode Systems

Gas-Sensing Probes:

  • Microporous materials- manufactured from hydrophobic polymers that have a porosity of about 70% and a pore size of less than 1m, and are about 0.1mm thick.

  • Homogeneous films- solid polymeric substances through which the analyte gas passes by dissolving in the membrane, diffusing, and then desolvating into the internal solution. They are usually thinner than microporous in order to hasten the transfer of gas and thus the rate of response of the system.


Molecular selective electrode systems19 l.jpg

Molecular-Selective Electrode Systems

Gas-Sensing Probes:


Instruments for measuring cell potentials l.jpg

Instruments for Measuring Cell Potentials

  • Direct-Reading Instruments

  • Commercial Instruments

    • Utility

    • General-purpose

    • Expanded-scale

    • Research


Direct potentiometric measurements l.jpg

Direct Potentiometric Measurements

  • The Sign Convention and Equations for Direct Potentiometry

  • The Electrode Calibration Method

    • Inherent Error in the Electrode

    • Activity Versus Concentration

  • Calibration Curves for Concentration Measurement

  • Standard Addition Method

  • Potentiometric pH Measurements with a Glass Electrodes

    • Summary of Errors Affecting pH Measurements with the Glass Electrode

    • The Operational Definition of pH


Potentiometric titrations l.jpg

Potentiometric Titrations

Schematic representation of an automatic potentiometric titrator devised by Lingane in 1948.


References l.jpg

References

http://ull.chemistry.uakron.edu/analytical/Potentiometry/

http://chem.ch.huji.ac.il/~eugeniik/instruments/electrochemical/potentiometric_titrators.htm

http://www.fz-juelich.de/isg/sensorik/bcs-isfet-e.html

http://www.chemistry.msu.edu/courses/cem333/Chapter23,potentiometry.PDF


  • Login