Student Question

Can the concentration of the salt bridge be anything for this experiment to work?


Quick answer:

Changing the concentration of one solution in the cell will increase the voltage potential of the cell because you are putting the system further out of equilibrium. Because the concentration in only one side of the cell has changed, the concentration gradient across both sides of the cell becomes steeper. In order for this experiment to work, the salt bridge must be concentrated enough to effectively separate the two electrolyte solutions, but it must also be porous enough to allow ionic flow.

Expert Answers

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In a galvanic cell, the reason the voltage is generated is because of the combined electric potentials of the two metals in the metal sulfate solution of the electrolyte.  If you increase the concentration of one of the electrolyte solutions, you increase the number of cations and anions (depending upon which electrolyte you increase), thus increasing the voltage potential of the cell.

In a galvanic cell, when a current flows in the circuit, equilibrium conditions are not achieved and the cell potential will usually be reduced by various mechanisms, such as the development of overpotential.  It is also important to note since chemical reactions occur when the cell is producing power, the electrolyte concentrations change and the cell voltage is reduced, the longer the cell operates.

The concentration of the salt bridge has to be such that it effectively separates the two electrolyte solutions, but porous enough to allow the steady exchange of cations and anions between the two electrolytes.

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