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Thread: Electrolysis

  1. #1 Electrolysis 
    Forum Masters Degree thyristor's Avatar
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    Could anyone give me a good explanation of why ions are needed to be in a liquid from the start if you want to conduct an electric curent through the liquid?
    I mean, take water for example. Why aren't the water molecules splt up in hydrogen and hydroxide ions when you lower down your electrodes in the liquid?


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  3. #2  
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    The electricity does not really "split" a water molecue into its components. The negative electrode merely dumps electrons onto positively charged species in its vicinity. Similarly, the positve electron accepts electrons from negative species. That's why in electrochemistry, we talk about half-reactions occurring at each electrode.

    Electrolysis of pure water can proceed in principle because there is already a trace of ionization of the water molecules. But it would occur at an extremely slow pace. Recall that the ionization constant of water is only about 10 exp-14. That's ridiculously small, way too small to support a significant current between electrodes. The electrical resistance of pure water is enormously high.

    Adding additional salts or acid as electrolytes provides many more ions to support a large current. Electrolysis can now proceed and a rapid pace.
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