Construction and Working of Indicator Electrodes are electrodes that respond to the activity of ions in a solution. Their potential varies depending on the concentration of a particular ion. Common types include metal electrodes and glass electrodes.
1.Metal Electrodes is Construction and Working of Indicator Electrodes
Construction:
Metal electrodes, such as platinum or gold, are simple electrodes made from a piece of metal.
These metals are chosen for their inertness and high conductivity.
Working:
Metal electrodes are used to detect redox reactions where the metal either gains or loses electrons in response to a change in ion concentration in the solution.
For example, in a redox reaction, a platinum electrode may participate in the following half-reaction:
${Fe^{3+}_{(aq)} + e^- Fe^{2+}_{(aq)}}$
The electrode potential changes depending on the concentration of and ions in the solution.
2. Glass Electrode is Construction and Working of Indicator Electrodes
Construction:
The glass electrode is a specialized ion-selective electrode (ISE) used primarily to measure pH (concentration of H⁺ ions).
It consists of a thin glass membrane that is selective to hydrogen ions. Inside the glass membrane is a solution of known pH (typically a buffer solution), with an internal reference electrode (such as Ag/AgCl).
The electrode body is filled with an internal electrolyte solution and sealed. A reference electrode, like a calomel or Ag/AgCl electrode, is used as the external reference.
Working:
The glass membrane allows the selective passage of H⁺ ions from the test solution into the internal buffer solution.
The potential difference across the glass membrane is a function of the hydrogen ion concentration in the test solution.
The Nernst equation governs the response of the glass electrode:
$E = E^\circ + \frac{RT}{F} \ln[H^+]$
Where:
E is the measured potential,
E∘ is the standard electrode potential,
R is the universal gas constant,
T is the temperature in Kelvin,
F is the Faraday constant, and
[H+] is the hydrogen ion concentration (pH).
The electrode provides a potential that varies linearly with the logarithm of the hydrogen ion concentration (pH). As pH changes, the electrode potential changes, enabling precise pH measurement.