Chemistry project

1. CALOMEL ELECTRODE
CH.SRAVAN
Roll.no:22H51A6272

2. REFERENCE ELECTRODE:
A ‘Reference electrode ’ is an electrode which has a
stable and well-known potential.
• It is used as half cell to build an electrochemical cell to
determine the other electrode potential.
• There are two types of Reference electrodes.They are:
1. Primary Reference electrode.
Ex:Standard hydrogen electrode.
2.Secondary Reference electrode.
Ex:Calomel electrode,Glass electrode.

3. CALOMEL ELECTRODE:
**Calomel electrode is a
secondary reference
electrode.
** It is used for measuring
Electrode potential.

4. CONSTRUCTION:
• It consists of a glass tube having a side tube on eachside.
• Mercury is placed at the bottom of a glass tube.
• Surface of Hg is covered with a paste of Mercurous chloride.
• A solution of KCl is then placed over the paste through the
side tube present on the right side.
• A Platinum wire dipping into the mercury layer is used for
making electrical contact.
• Left side of the tube is used for making electrical contact
with a salt bridge.

5. CELL REPRESENTATION:
•Hg,Hg2Cl2/ KCl(Saturated solution)
• The standard reduction potential of calomel electrode at
25⁰C :
1. For saturated KCl solution,E=0.24V
2. For 1N KCl solution,E=0.28V
3. For 0.1N KCl solution,E=0.33V
• The potential of calomel electrode depends on the
concentration of KCl solution.

6. CELL REACTIONS:
• Calomel electrode acts as both cathode and anode depending on the
nature of another electrode of the cell.

7. APPLYING NERNEST EQUATION:
• E cell = E⁰ cell –(0.0592/n)log([Hg]²[Cl-]²/[Hg2Cl2]
• n = number of electrons = 2
• [Hg] ,[Hg2Cl2 ] are in equimolar ratio .
• So,both of them can be cancelled.
• E cell = E⁰ cell –(0.0592/2)log[Cl-]²
• E cell = E⁰ cell –(0.0592/2)×2log[Cl-]
• E cell = E⁰ cell – 0.0592log[Cl-]
• The Calomel electrode is reversible with respect to
the concentration of Cl- ions.

8. ADVANTAGES:
• It is convenient to handle and easy to construct.
• No separate salt bridge is required for its combination
with other electrode.
• The potential of the electrode is reproducible and
remains constant.
APPLICATIONS:
• Calomel electrode is used in voltmeters and PH meters.