Redox Titration - type of titration in which the Ecell are monitored
Redox Titration Indicators
A) Iodine (I2)
B) Starch
C) colorless to blue
D) Na2S2o3 (Sodium Thiosulfate)
E) Starch
F) Blue to colorless
G) KMnO4
H) Self indicating
I) Colorless to purple
J) K2Cr2O7
K) Diphenylamine
L) Colorless to purple
Auxillary Oxidizing/Reducing Agents - used in analytes prior to titration to convert them into the desired ionic forms
Reducing Agents:
Jones Reductor
Walden Reductor
Jones Reductor – uses metal amalgams for prereduction of the analytes
Walden Reductor – uses Ag for prereduction of the analytes
Oxidizing Agents
Sodium bismuthate
Ammonium peroxydisulfate
Hydrogen peroxide
Sodium bismuthate - oxidizing agent used in converting Mn2+ to MnO4 -
Standard Reducing Agents
Iron (II) solution
Sodium thiosulfate
Standard Oxidizing Agents
Potassium permanganate
Cerium (IV) solution
Potentiometry - when the pair of electrodes is placed in the sample solution it shows the potential difference by the addition of the titrant or by the change in the concentration of the ions.
Potentiometry works with these electrodes:
Reference Electrode
Indicating Electrode
Electrodes - are mainly used to measure the voltages.
Reference electrode – these are mainly used for the determination of the analyte by maintaining the fixed potential.
Examples of reference electrodes:
Standard hydrogen electrode
Ag/AgCl electrode
Saturated calomel electrode
Indicator electrode - it is used to measure the potential of the analyte solution comparing with that of reference electrode.
The potential of indicator electrodes are directly proportional to ion concentration.
Examples of Indicator electrode:
Hydrogen electrode
Glass electrode
Antimony-antimony electrode
Reference electrodes have two types:
Primary standard electrodes
Secondary standard electrodes
Primary standard electrodes
Standard hydrogen electrode
Secondary standard electrodes
silver-silver chloride electrode
saturated calomel electrode
Three classes of indicator electrodes:
Metal indicator electrodes
Membrane electrodes
Ion-selective electrodes
Metal indicator electrodes:
First kind electrodes - metal rods
Second kind electrodes - metals coated with precipitates
Third kind electrodes - inert electrodes
Membrane electrodes - are used to determine p-values:
pH
pCa
pNO3
Voltammetry - an electroanalytical technique that gives information about the analyte. We can even measure the amount of current by varying the voltage.
Voltammogram - change in current with the varying voltage gives the plot
Voltammetry is a three-electrode system including:
Working electrode
Reference electrode
Auxiliary electrode
Three-electrode system:
A) Working electrode
B) Auxiliary electrode
C) Reference electrode
Working electrode - ranges from small mercury to flat platinum disc
Commonly used working electrode materials:
Gold
Platinum
Glassy carbon
Depending on the choice of working electrode, the type of voltammetry is decided.
Dropping Mercury Electrode - is used in Polarography technique
Platinum electrode - Cyclic Voltammetry
Glassy Carbon electrode - used in Linear Sweep Voltammetry
Reference electrode - uses standard electrode where the potential is kept constant. It provides potential to the Working electrode.
Common reference electrodes:
Calomel electrode
Ag/AgCl electrode
Auxiliary electrode - usually a thin platinum wire. It serves merely to carry the current flowing through the cell
Usually, redox reaction occur simultaneously at the auxiliary electrode.
Polarography - branch of voltammetry in which a dropping mercury electrode (DME) is used as the working electrode.
Polarography:
Wide cathodic potential range and a renewable surface
Widely used for the determination of many reducible species