Question

The calomel electrode used as a reference electrode contains:
(A)- $Pb{{O}_{2}}-PbS{{O}_{4}}$mixture
(B)- $HgC{{l}_{2}}$
(C)- $H{{g}_{2}}C{{l}_{2}}$
(D)- $ZnC{{l}_{2}}$

Answer 1

Hint: An electrode which has a stable and well-known electrode potential is known as a reference electrode. Calomel electrode is an electrode consisting of calomel, mercury, and a solution of potassium. The calomel electrode is used as a reference electrode.

Complete Step by step answer:
-A reference electrode can be used in many ways, but the simplest way is to use it as a half-cell to build an electrochemical cell which allows the potential of the other half cell to be determined.
-A reference electrode which is based on the reaction between elemental mercury and mercury (I) chloride is known as the saturated calomel electrode, abbreviated as SCE.
-In the calomel electrode, a small amount of mercury is placed at the bottom of the broad tube and is then covered with a saturated paste of Mercurous chloride $(HgC{{l}_{2}})$and mercury.
-The cell notation for saturated calomel electrode is written as-
$C{{l}^{-}}(4M)|H{{g}_{2}}C{{l}_{2}}(s)|Hg(l)|Pt$

So, the correct answer is option C.

Note: The saturated calomel electrode has many applications in electrochemistry. Saturated calomel electrode is used in pH measurement, cyclic voltammetry, and in general aqueous electrochemistry. A type of potentiodynamic electrochemical measurement in which the working electrode potential is ramped linearly versus time is known as Cyclic voltammetry, abbreviated as CV. Mercury and mercury (I) chloride in a saturated calomel electrode is widely replaced by the silver chloride electrode. The working of the silver/silver chloride reference electrode and the saturated calomel electrode are the same. In both the electrodes, the activity of the metal ion is fixed and is dependent on the solubility of the metal salt. There is a disadvantage for the usage of the saturated calomel electrode. The calomel electrode contains mercury, which poses much higher and greater health hazards in the form of mercury poisoning.