When two metals having different electrical potentials are placed in a solution of an electrolyte (such as a lemon or an orange,
with its high concentration of citric acid), a crude electrochemical cell is set up. The cell is a voltaic cell resulting from a spontaneous oxidation–reduction reaction.
The open-circuit potential difference between the reactions at each electrode is the cell potential, which can be measured with a digital voltmeter or a voltage sensor. The more active metal in a pair is usually the negative electrode (the anode). Magnesium, for example, which is the most active metal that was tested, always appears as the anode. (Aluminum is a significant exception to this general trend.) Significant bubbling is observed when magnesium is used as the electrode.
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