1. B] Describe the construction and working of calomel electrode
Answer:
CALOMEL ELECTRODE:
Construction:
Calomel Electrode is a Secondary Reference electrode. It consists of a drop of mercury at the bottom, over which a paste of mercury-mercurous chloride is placed. A solution of saturated solution of potassium chloride is filled inside the glass tube. A platinum wire sealed to the bottom of glass tube is taken out for making the electrical contact. This reference electrode is connected to other electrode system by the help of the side tube which serves as salt bridge.
Working:
It is a reversible electrode. It undergoes both oxidation and reduction depending upon the other electrode (Half-cell) in contact. If it acts as anode, undergoes oxidation add vice versa.
It is represented as KCl(satd)│ Hg2Cl2(satd)│ Hg
Half-cell for Calomel Electrode:
The net reaction involving both anode and cathode is,
The potential of the calomel electrode depends upon the concentration of the potassium chloride solution. The reduction potentials of the calomel electrodes on hydrogen scale at 298K are as follows: Saturated KCl0.2415 V1.0N, KC1 0.2800 V&0.1NKCl0.3338 V.
Advantages:
- Simple to Construct.
- Electrode potential is reproducible and constant for long period.
- Used as reference electrode to measure pH.