PHYSICAL CHEMISTRY IN BRIEF

CHAP. 11: ELECTROCHEMISTRY [CONTENTS] 397

Example

The Daniell cell is an example of a galvanic cell. It is formed by two half-cells. One of them

is a zinc electrode surrounded by a solution of zinc sulfate, and the other is a copper electrode

surrounded by a solution of copper sulfate. The zinc electrode is the anode at which oxidation

proceeds

Zn = Zn2++ 2 e−.

The copper electrode is the cathode at which reduction proceeds

Cu2++ 2 e−= Cu.

We add up the reaction at the anode and that at the cathode to obtain the overall reaction

taking place in the cell

Zn + Cu2+= Zn2++ Cu.

If the electrodes are connected by a first-class conductor, electrons travel through the conductor

from the anode to the cathode.

If the solutions of ZnSO 4 and CuSO 4 are separated by a frit, the zinc ions travel through the frit

from the anode to the cathode while the sulfate ions travel in the opposite direction. The liquid

potential originates at the interface.

11.8.2 Symbols used for recording galvanic cells

Galvanic cells are schematically recorded in a line, with the following conventions applied:

• The anode is written on the left, the cathode on the right. Their charges may, but do
  not have to, be marked.


• The phase interface is marked by a single vertical bar ”|”. We find it at the place of
  contact of the electrode and the electrolyte, two electrolytes separated by a frit, or at
  the place of contact of an undissolved salt and a metal in the case of electrodes of the
  second type, see11.8.10.


• If there is a salt bridge suppressing the diffusion potential at the place of contact of two
  electrolytes, we write a double vertical bar ”||” instead of a single one.