What are the electrochemical reactions found in Ag/AgCl and Hg/Hg2Cl2 electrodes, and what are their common names. Why do we use them in electrochemical measurements? (Look at Notebook for how to solve related problems)
Ag/AgCl- Called a Silver-Silver Chloride electrode, and its reaction is AgCl+e = Ag + e = Ag+Cl-Hg/Hg2Cl2 – Called a Calomel electrode, and its reaction is 1/2Hg2Cl2 (s) + e = Hg(l) + Cl-We use these reference electrodes because the absolute electic potential of a point is not simply defined, so we need a reference point’s potential so that we can take the difference of the reference and the potential
Ag/AgCl and Hg/Hg2Cl2 electrodes are common reference electrodes used in electrochemical measurements. They work based on electrochemical reactions that occur at the electrode surface.
At the Ag/AgCl electrode, the half-reaction occurring is:
AgCl(s) + e⁻ ⇌ Ag(s) + Cl⁻(aq)
This half-reaction is known as the reduction of silver chloride. At equilibrium, the electrode potential is defined as E = E⁰ + (RT/nF)ln([Ag⁺]/[Cl⁻]), where E⁰ is the standard electrode potential, R is the gas constant, T is the temperature in Kelvin, n is the number of electrons transferred in the reaction, F is Faraday’s constant, and [Ag⁺]/[Cl⁻] is the concentration ratio of silver ions to chloride ions in solution. The standard electrode potential for the Ag/AgCl electrode is +0.197 V.
At the Hg/Hg2Cl2 electrode, the half-reaction occurring is:
Hg2Cl2(s) + 2e⁻ ⇌ 2Hg(l) + 2Cl⁻(aq)
This half-reaction is known as the reduction of mercury(II) chloride. At equilibrium, the electrode potential is defined as E = E⁰ + (RT/nF)ln([Hg²⁺][Cl⁻]²/[Hg2Cl2]), where E⁰ is the standard electrode potential, R is the gas constant, T is the temperature in Kelvin, n is the number of electrons transferred in the reaction, F is Faraday’s constant, and [Hg²⁺][Cl⁻]²/[Hg2Cl2] is the solubility product constant for mercury(II) chloride. The standard electrode potential for the Hg/Hg2Cl2 electrode is +0.268 V.
Ag/AgCl and Hg/Hg2Cl2 electrodes are used as reference electrodes because they have stable and well-defined electrode potentials, which can be used to measure the electrode potential of other electrodes. Additionally, the electrolytes used in these electrodes are not easily contaminated or affected by other chemical species in solution, which helps to ensure the accuracy and reproducibility of electrochemical measurements.
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