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Can a covalent or metallic compound substitute a salt bridge in a battery?

 
 
sorin
 
Reply Thu 24 Oct, 2013 08:17 am
A simple experiment is proposed below:
The ,,positive” electrode is formed by a Cu piece inserted into a glass of water (or a CuSO4 solution). The ,,negative” electrode is formed by a Zn piece inserted into water or into an acid solution (vinegar, citric or sulfuric acid). Vinegar and citric acid are commonly used in food preparation so it is not a big deal to find them. For a more spectacular visual effect, a solution of sulfuric acid, 3 up to 5M can be used in Zn electrode chamber.
Common tap water can be used. Of course for more elaborated experiments or for the skeptics deionised water is necessary; for home experiments this can be bought from a car shop.
As salt bridge, a covalent compound (graphite) or a metal which does not react with electrolytes (Pt, Au) is used. For graphite, it is possible to arrange a geometrical form in a U shape only from graphite components, or to use two pieces of graphite connected with a metallic conductor. For the simplest setup, two graphite electrodes recovered from used batteries are used. Two graphite pieces recovered from a pen are another available option.
With this set up, an electric current of about 30 μA is counted on the ammeter when in the Zn electrode chamber, water is used. After long time of working, the Zn electrode is consumed, and at Cu electrode no visual modifications are observed.
An electric current of about 50 μA is counted on the ammeter, when in the Zn electrode chamber, vinegar is used as electrolyte. After long time of working, the Zn electrode is consumed, and at Cu electrode no visual modifications are observed. Bubbles of hydrogen develop on Zn electrode.
An electric current from 50 μA up to 5 mA is counted on the ammeter, when in the Zn electrode chamber, a sulfuric acid on growing concentration is used as electrolyte.
When sulfuric acid is used, at Zn electrode it can be clearly observed the release of hydrogen gas simultaneously with rapid Zn electrode consume (fig. 4). Formed ZnSO4 gives opalescence in the compartment and starts to sediment when quantity produced is greater then its solubility. At Cu electrode no visual effects are observed.
You can find the details of the experiment at
Edit [Moderator]: Link removed under basics of physical chemistry book.

As can be observed in this simple battery, both ,,oxidation” and ,,reduction” phenomena take place at the same electrode (Zn electrode), and, in the same time, a electric current is counted in external circuit.
Secondary, a non ionic salt bridge is used so again, the movement of ions as compensation for a current in the external circuit does not need any comment.
The framework for the conversion of chemical energy in electric energy is completely changed.
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