Salt Bridge - Uses

Uses

As electrons leave one half of a galvanic cell and flow to the other, a difference in charge is established. If no salt bridge were used, this charge difference would prevent further flow of electrons. A salt bridge allows the flow of ions to maintain a balance in charge between the oxidation and reduction vessels while keeping the contents of each separate. With the charge difference balanced, electrons can flow once again, and the reduction and oxidation reactions can proceed. In general, keeping the two cells separate is preferable from the point of view of eliminating variables from an experiment. When no direct contact between electrolytes is allowed, there is no need to make allowance for possible interactions between ionic species.

The technique more specifically allows freedom in the choice of ions in solution. For instance, a mixture of two different cations in solution might result in the preferential reduction of the wrong one, for the purposes of the experiment. With a salt bridge, the desired cation (positive) species is isolated in one vessel while the cation in the other vessel may be chosen to make the experiment easier, such as using a more soluble, or more stable salt of the anionic (negative) species.

If the two vessels are entirely disconnected, without a salt bridge, then the cation and anion species are also isolated, but then each species quickly reaches equilibrium because no electrical current can flow. The salt bridge can be seen as a way of completing the ionic circuit without letting the solutions intermix.