Voltaic cells utilize spontaneous redox reactions to produce electrical energy. Each cell consists of the following components:

• 2 electrodes
• 2 electrolytes
• porous boundary (salt bridge or porous porcelain cup)
• external circuit

A voltaic cell consists of two half-cells. Each half-cell contains one electrode and one electrolyte.

The two half-cells are connected by the porous boundary and an external circuit. The porous boundary separates the two electrolytes, but permits ions to move between the two solutions through tiny openings in the cotton plugs of a salt bridge or in the walls of a porcelain cup. This flow of ions maintains the electrical neutrality of the system. The figures shown below show two variations of the porous boundary.

In an voltaic cell, the strongest reducing agent always undergoes oxidation at the anode, while the strongest oxidizing agent in the cell always undergoes reduction at the cathode.

A voltaic cell can be represented using abbreviated notation, referred to as cell notation. In this notation, a single line indicates a phase boundary, such as the interface between an electrode and an electrolyte in a half-cell. A double line represents a porous boundary such as a salt bridge. A common practice is to write the anode on the left and the cathode on the right.

anode(-)| electrolyte || electrolyte |cathode(+)

Consider a voltaic cell that utilizes copper and zinc half-cells.

\( \mathrm { Zn(s)~ |~Zn^{2+}(aq)~ || ~Cu^{2+}(aq)~ |~Cu(s) } \)

This voltaic cell can be assembled using a U-shaped tube or an unglazed porcelain (porous) cup. Refer to the diagrams below.

Check Your Understanding

Complete Questions 1, 2, 3, 4, and 5 on page 626 of the textbook. Click the link below to check your answers.