This video describes the principle of potentiometric titrations. It also tells about the different types of potentiometric titrations and suitable electrodes. It describes the procedure for FeSO4 vs K2Cr2O7 redox titration. The different ways of determining the end point or equivalence points using the redox titration curve, first derivative curve and second derivative curve. It lists the advantages, disadvantages and applications of this technique.
Potentiometric titration is a technique similar to direct titration of a redox reaction. It is a useful means of characterizing an acid. No indicator is used; instead the potential is measured across the analyte, typically an electrolyte solution. To do this, two electrodes are used, an indicator electrode (the glass electrode and metal ion indicator electrode) and a reference electrode. Reference electrodes generally used are hydrogen electrodes, calomel electrodes, and silver chloride electrodes. The indicator electrode forms an electrochemical half cell with the interested ions in the test solution. The reference electrode forms the other half cell.
Potentiometric titration is a titration used to measure the amount of an analyte present in the given solution by measuring the change in the potential by a suitable indicator electrode, as a function of volume of titrant.
Potentiometric titration : Types
Redox reaction
Acid-Base (Neutralisation )
Complex formation reaction (Complexation)
Precipitation
Inert electrodes – Redox reaction
When dipped in the analyte solution, it indicates the potential of the bulk solution
Metallic electrode – Pt, Au, Ag etc.
Other conductive electrodes – Graphite, glassy carbon etc.
Nernst equation
Ion-selective electrodes - It responds to the change in the activity or concentration of a particular species in the analyte solution.
Glass electrode – Acid-Base titration – measurement of pH (H+ ions )
Liquid-ion-exchanger electrodes, solid-state ion-selective electrodes, Coated-wire electrodes, Field-effect transistor electrodes
Neutral-carrier ion-selective electrodes - Complexometric titration
Gas-sensing electrodes  - used to monitor dissolved gases
Biomembrane electrodes – enzyme catalysis
Redox reaction - Pt, Au, Ag etc.
Acid-Base (Neutralisation) – Glass electrode or Combined glass and reference electrode
Complex formation reaction (Complexation) – Mercury-coated silver electrode, Neutral-carrier ion-selective electrodes
Precipitation - Silver indicating electrodes, ion selective electrodes
Reference Electrode: Calomel electrode
Indicator Electrode: Pt electrode
Analyte solution : FeSO4 (or) Ferrous ammonium sulphate + H2SO4
Titrant : K2Cr2O7
Acid-Base/Neutralisation reaction
Reference Electrode : Calomel electrode or Ag/AgCl electrode
Analyte solution : Acid/Base
Titrant : Base/Acid
Indicator Electrode : Glass electrode
Advantages of Potentiometric titration :
Used for coloured solutions
Suitable for turbid, fluorescent solutions
Suitable for dilute solutions
Uses small quantities of the sample
Special care is not required at the end point, as it is determined graphically- Can obtain sharp and accurate end point.
Does not require indicators.
Disadvantages of Potentiometric titration :
Accurate known concentration of solutions is required.
Labour intensive and time consuming measurements.
Highly pH sensitive.
Applications of Potentiometric titration :
Clinical chemistry – analysis of metals.
Pollutants in water such as metal ions, cyanide, fluorides, ammonia
Agriculture - Determination of various elements in soil, fertilizers etc.
Food processing industries
Detergent manufacturing industries
Other industries such as cosmetic, textile, paper, paint, explosive, energy etc.

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