CALOMEL ELECTRODE - REFERENCE ELECTRODE.

Calomel electrode
Reference electrode
Silver Chloride electrode

1. A ARTS AND SCIENCE
COLLEGE COIMBATORE 008

NAME : SABARIDARAN B
ROLL NO : 20BMB042

LASS : | Bsc. MICROBIOLOGY ú
UBJECT : BIO ANALYTICAL, N UE
ORIG : CALOM

E —_

2. REFERENCE ELECTRODE

An ideal reference e
constant potenti.
of the amount of
through it.

e is one that maintains a

) that is passed

3. Voltammetric methods are those in which curre
passing in an electrochemical cell is measured as a
function of the potential applied to the working
electrode. Potential, by definition, is not something
that can be directly mi d. Rather, the
measurement of ap d potential requires that a
reference point firs lished, and individual

potentials be measu slative to that reference
point. This is accom hed by placing a second
electrode, called the nce electrode, in the cell
and measuring potential as the energy difference
between the two electrodes, called = ©

electro

4. Reference electr

half-cell com
with changin:
values of acti
reproducible

be constructed using
able over time and
sent at well-defined
)JOSsess fixed,

de

S.

5. The reference half-cell with which most of us

are familiar is the standard hyd aaa
ecos fm (SHE) inert solid
e platinum gas is
adsorbed, im containing
hydrogen ions a > half-cell
reaction for

H* +e

6. The potential of the standard
hydrogen electrode is arbitrarily
assigned the value of zero (0.000)
volts at 25% C. When standard
hydrogen electrode is coupled with
another electrode, the EMF of the cell

thus formed will evidently be equal
to the potential of that electrode to
which it is coupled. The potentials
obtained in this way are called
relative potentials, or e/ectrode
potentials on the hydrogen scale.

7. Practical application of the SHE is limited by the
difficulties in preparing sc

unit activity and m: nit activity for H2
(g) in the half-cell. pel ents carried out
in aqueous solution ne Of two other

common referen he saturated
calomel electroc E i
chloride electro

8. Calomel electrode is most widely used as secondary reference
electrode. The standard calomel electrode (SCE) comprises of
wide glass — tube fitted wi nar side tubes. Pure mercury is
placed at the bottom of the and covered with a paste
of mercurous chloride (c olution of KCI is introduced
above the paste. A lution may also be used. A
Pt wire sealed into used to make electrical
contact. The side tul solution provides the salt
bridge, which connects any other electrode.

The calomel electrode

And the half-cell reaction is written as
Hg2Cl, + 2e > 2Hg + 2CF

9. Lead to pH-meter &

Platinum wire

Hg

H9/H 920 12 paste
Saturated KCI
Porous plug

Saturated Calomel Electrode
Electrode is mercury coated with calomel (Hg,Cl,)

Electrolyte is a solution of potassium chloride.

10. INN Chloride Electrode
(A/A

The silver/silver chloride reference electrode is
composed of a silver wire (Ag) that has been
coated with a layer of solid silver chloride
(AgCl), immersed in a solution that is saturated
with KCI and AgCl. The half cell reaction is

AgCl (s) + e - Ag (s) + Cl” (satd)

11. Both the SCE and the Ag/AgCl reference
electrodes offer stable half-cell potentials that
do not change over time

12. THANK YOU!