Potentiometry

It is a technique which is used to identiy and analyse metal or non metal ions by measuring potential difference

Two types:

1. Electrolytic cell
2. Electrochemical cell (galvanic cell)

Nerst equation #

$$ \begin{align} E_{cell}=E_{cathode}-E_{anode}\\ =\left(E\degree_{cathode}+\frac{RT}{nF}\log\frac{left}{right}\right)-\left(E\degree_{anode}+\frac{RT}{nF}\log\frac{left}{right}\right)\\ =(E\degree_{cathode}-E\degree_{anode})+\frac{0.059}{n} \log(…) \end{align} $$

Types #

Types of electrodes based on application #

1. Standard electrodes
   1. Also known as reference elecrodes whose potential is assumed to be zero.
   2. Other standard or reference electrodes are Ag/AgCl, Hg/Hg₂Cl₂, SCE, SHE
   3. Reference electrodes are those elecrodes whose potential does not change much over a wide variety of concentrations and a long period of time.
2. Working electrodes:
   1. They are the type of elecrodes whose potential changes due to a particular chemical reaction taking place on its surface.

Types of electrodes based on chemical reactions #

1. Electrodes of first kind
   1. They are defined as half cells where a metal or a nonmetal substance is dipped into a solution containing its own ions.
   2. Potential determining ions: The ions whose concentration influence the potential of the electrode is called potential determining ions.
2. Electrodes of second kind
   1. They are defined as half cells where a metal is coated with its sparingly soluble salt and dipped into solution containing its ions.
3. Gas electrodes (H2,O2,Cl2)
   1. They are half cells where a inert platinum wire is passed through a sealed glass tube containing an ioinisable gas and dipped into a solution containing the ions of the gas.
   2. Q. Why platinum is only used is gas electrodes?
      1. Platinum is inert so it does not react and produce any other ions
      2. Platinum provides a very good catalytic surface for the exchange and transfer of electrons
4. Redox electrodes
   1. They are half cell where a Pt wire is dipped into a solution containing the same ion in two different oxidation states.
5. Amalgam electrodes
   1. They are half cells where a metal amalgam is dipped into a solution containing its ions.
6. Glass electrode