Page 89 - A Working Method Approach For Introductory Physical Chemistry Calculations

Electrochemistry I: Galvanic Cells 73
Summary:

Cathode reaction: CU2+(aq) + 2e + CU'(~) Eo = +0.34V
Anode reaction: Zno(s) + Zn2+(,,) + 2e E" = -0.76V

Net cell reaction: CU2+(aq) + Zn'(,) + CU'(,) + Zn2+(aq)
EOcell = + 1.1ov

Cell Diagrams
Galvanic cells can be represented by a shorthand notation called a cell
diagram. For the Daniel cell, this one-line representation of the cell is
given as:

The short vertical lines represent phase boundaries or junctions. The
two vertical lines in the centre represent a device called a salt bridge,
which has three functions:
1. It physically separates the two electrodes, i.e. the cathode and the
anode.
2. It provides electrical continuity within the galvanic cell, i.e. a
path for migrating cations and anions.
3. It reduces the so-called liquid junction potential. This is a voltage
or potential generated when two dissimilar solutions are in
contact with each other. Such a potential is produced as a result
of unequal cation and anion migration across a junction. A salt
bridge, as its name suggests, consists of ions (charged species),
which migrate at practically equal rates. An example of such a
species is the inorganic salt potassium nitrate, KN03, which
consists of K+ cations and NO3- anions respectively.

In the one-line representation of the cell, the cathode (where
reduction takes place; 'CROA') by convention is shown on the right-
hand side, and the anode (where oxidation takes place) is written on
the left-hand side, i.e. for a galvanic cell this takes the form:
1 Anode (Oxidation) 11 Cathode (Reduction)

RHE
LHE
Therefore, in the Daniel cell, at the anode, metallic zinc gives up 2e
to form Zn2+(,,) ions. These electrons move from the anode and