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Chloride flows down its concentration gradient into the cell. At a certain point a minute amount of net positive charge develops on the outside, enough to electrostatically attract chloride ions back out and thus counterbalance the flow inwards due to the concentration gradient(thus achieving equilibrium). This would mean that the negative chloride ions INSIDE of the cell are furthest from the positive electrical field that develops OUTSIDE the cell(and thus have the highest potential,Picture below to illustrate.The big Q shows the attractive positive charges that develop outside the cell attracting the negative chloride(-q) to it)

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Then Chloride naturally flows back out to the lower potential. The Nernst equation on the other hand(which takes into account each ion individually so the Sodium and Potassium in the picture above isn't interrupting in anyway) says that the equilibrium resting potential for chloride is -70mV (at the concentrations indicated in the first picture) inside the cell relative to the outside(Outside the cell is always taken as the reference point in calculating equilibrium potential) How could this be though?? This would mean Chloride is flowing from a Low potential to a High Potential(When the natural order of things is High to Low). The only thing I could think of was the inside is actually a higher potential relative to the outside so that when we use the formula where Voltage=(Intracellular Potential energy - Extracellular Potential energy)/Charge we get (70-0)/-1=-70mV(basically it's just the negative sign of the charge that confuses everything)

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The issue is this:

This would mean Chloride is flowing from a Low potential to a High Potential(When the natural order of things is High to Low)

Positive charges move from higher to lower potential. However, since chloride ions are negatively charged, they actually want to move from lower to higher potential. This is because they want to move to lower potential energy, which for negative charges means higher potential because $\Delta V=\Delta U/q$. You can see this in the diagram with the two charges you have supplied. The negative charge wants to move towards the positive charge, which is towards higher potential (and lower potential energy).

Of course this neglects effects of concentration (chemical potential). Both need to be considered. The Nernst potential is the potential that needs to be applied to balance electrical and chemical gradients.

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