CHEMISTRY TEXTBOOK

Salt bridge is prepared by filling a U

tube with hot saturated solution of the salt

and agar agar solution allowing it to cool.

The cooled solution sets into a gel which does

not come out on inverting the tube. The salt

bridge is kept dipped in distilled water when

not in use as shown in Fig. 5.5.

i. The metal electrodes or the inert electrodes

are denoted by vertical lines placed at the

ends of the formula or the short notation.

The anode (-) is written at the extreme

left and cathode (+) at extreme right.

ii. The insoluble species if any or gases are

placed in the interior position adjacent to

the metal electrodes.

iii. The aqueous solutions of ions are placed

at the middle of the cell formula.

iv. A single vertical line between two phases

indicates the phase boundary. It indicates

the direct contact between them.

v. A double vertical line between two

solutions indicates that they are connected

by salt bridge.

vi. The additional information such as

concentration of solutions and gas

pressures is also given.

vii. A single half cell is written in the order:

aqueous solution of ions first and then

the solid electrode.

For example Zn^2 ⊕(1M) Zn (s). This

order is reversed when the electrode

acts as anode in the cell. The following

example illustrates these conventions.

The cell composed of Mg (anode) and

Ag (cathode) consists of two half cells,

Mg^2 ⊕ (1M) Mg (s) and Ag⊕ (1M)Ag(s).

The cell is represented as :

Mg (s) Mg^2 ⊕^ (1M) Ag⊕(1M) Ag(s).

Try this...

Salt bridge can be prepared

with a laminated long strip of good

quality filter paper. Cut the two ends of

a laminated strip. Dip the two ends in a

saturated solution of KCl for 24 hours.

This strip can be used as salt bridge by

dipping the two ends in two solutions.

Functions of salt bridge

The salt bridge serves the following
functions :

i. It provides an electrical contact between
two solutions and thereby completes the
electrical circuit.

ii. It prevents mixing of two solutions.

iii. It maintains electrical neutrality in both
the solutions by transfer of ions.

5.6.2 Formulation or short notation of
galvanic cells : A galvanic cell is represented
by a formula or short notation that includes
electrodes, aqueous solutions of ions and other
species which may or may not be involved in
the cell reaction. The following conventions
are used to write the cell notation.

Can you tell?

You have learnt Daniel cell

in XI th standard. Write notations

for anode and cathode. Write the cell

formula.

5.6.3 Writing of cell reaction : The cell

reaction corresponding to the cell notation is

written on the assumption that the right hand

side electrode is cathode (+) and left hand

side electrode is anode (-).

Fig. 5.5 : Salt bridge

Saturated KCl

solution + agar gel

Glass

wool plugs

Beaker

Distilled water

U tube