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I struggle to understand the use of ion-permeable membrane (or salt bridge). https://en.wikipedia.org/wiki/Concentration_cell

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If i pour two solutions with different concentration, why do you need the junction between solutions ? Like this :

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According to my readings on Galvani's potential the electrode should be polarised with the potential of the solution their in. Hence you can calculate the concentration of unkown solution C2 without junction ?

In this page https://en.wikipedia.org/wiki/Salt_bridge it is said that the salt bridge is needed to avoid having one solution depleted of electrons and another full. Why the connection of electrode isn't creating equilibrium between solutions ?

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    $\begingroup$ You have no complete circuit. At best, there is an ultra-tiny and very short lived capacitive charging. And it is a bad capacitor at that: two beakers with a big air gap. Search around this site for salt bridges and answers asking why they are necessary. This one keeps coming up. $\endgroup$
    – Ed V
    Apr 20 at 19:53
  • $\begingroup$ Suppose one electron has left one of these solutions and gets to the other one. The solution rorm which it is coming becomes positively charged, and so will be reluctant to accept that a second electron would leave. Further more, the second solution becomes negatively charged, and will repell any second electron from coming. So no current could be established between the two solution. There may be a small tension, but no current. It is not a cell. $\endgroup$
    – Maurice
    Apr 20 at 20:27
  • $\begingroup$ Please see What happens inside salt bridges? $\endgroup$ Apr 20 at 22:16
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    $\begingroup$ Please avoid asking same question on multiple SE. I had a conversation with you on Physics SE . If you believe that this question cannot be answered on Physics SE than delete it from there or try migrating the original question to Chemistry SE. $\endgroup$ Apr 21 at 3:13
  • $\begingroup$ You must have heard about charge balance and what happens when charge disbalance occurs. 10 km long CG+ lightning needs charge that easily passes during just 1 minute of cell operation. $\endgroup$
    – Poutnik
    Apr 21 at 4:24

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