The Salt Bridge

Question 1

As mentioned, the salt bridge is an essential component of any galvanic cell. It serves two main functions:

Answer 1

1. Completes the circuit by allowing charged ions to flow between the two half cells.
2. Maintains cell neutrality by neutralising the build-up of charge in each half cell.

Question 2

How does the salt bridge work?

Answer 2

o In the anode 1⁄2 cell, oxidation is taking place and so positive ions are being produced. This causes a build-up of positive charge in the electrolyte. If left unchecked, the electrons would no longer move readily away from the increasingly positively charged half-cell.

o Similarly, in the cathode 1⁄2 cell, the reduction is taking place and removing positive ions from the solution. The 1⁄2 cell, therefore, becomes negative, and electrons would cease to move toward it.

o The salt bridge contains positive and negative ions.
o Negative ions migrate into the anode 1⁄2 cell to neutralise the build up of positive ions produced by oxidation.
o Positive ions migrate into the cathode 1⁄2 cell to neutralise the excess of negative ions leftover after reduction.

Question 3

What should the salt used in the electrolyte be?

Answer 3

The salt used in the electrolyte should be both unreactive and soluble. A good choice would therefore be KNO3 or NaNO3 (from UIV, recall that all salts of Na, K
and NO3 - are soluble).