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It seems to me that the cell setup of a galvanic cell is pretty much the same as in a potentiometric cell. However, galvanic cells just proceed the spontaneous direction of the net redox reaction of the anodic and the cathodic species in the cell, while in a potentiometric cell, it seems that the equilibrium activity ratios of the measured solution are not to be affected.

I've read that in a galvanic cell, current flows as to follow the natural tendency of electron flow--from the anode to the cathode. But in a potentiometric cell, it's said that the current of electrons flowing is kept to a minimum. How does a potentiometric cell does that? How does it avoid for reduction at the measured cell or oxidation at the reference electrode to happen?

P.S. I know that the question looks uncohesive, but it's because I'm really confused how these concepts occur. Please try to clear up the misconceptions that might have been apparent from my question.

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First, I wouldn't classify cells as potentiometric or galvanic.

If you take any electrochemical cell with non-zero total cell potential and connect a wire between the two electrodes it will discharge. This will happen spontaneously in the galvanic direction.

In potentiometric measurements of electrochemical cells, what you do is a potential measurement which ideally happens at zero current(definition of a voltmeter), and practically at picoampere or lower current. Therefore you are not allowing the electrons to flow from the outside circuit and hence your cell doesn't discharge.

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  • $\begingroup$ Ahh, but then you said that when you connect a wire between two electrodes mediating for a redox couple (that are practically possible to undergo spontaneous reaction), the reaction will automatically proceed to the more spontaneous direction, hence, electrons will be transferred and current will flow. So how will that current be minimized to picoamperes or lower magnitudes in a potentiometric setup? $\endgroup$ – Acnologia Dec 2 '17 at 13:13
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    $\begingroup$ That is the job of the instrument. The input impedance of the meter used is very high and doesn't allow appreciable currents to flow(this is also why standard voltmeters don't work in pH measurements). You may want to look into opamps with with FET inputs if you would like to see further details. $\endgroup$ – Burak Ulgut Dec 2 '17 at 19:41
  • $\begingroup$ Thank you!! That clears up much of my confusion regarding them. So it's really because of the voltmeters that potentiometric set-ups don't end up proceeding like a galvanic cell :) (I'm so mad at my books that they don't tell us those essential concepts,) $\endgroup$ – Acnologia Dec 3 '17 at 4:49
  • $\begingroup$ No problem. In their defense, at least one example does talk about this. 9th edition of Analytical Chemistry by Skoog, West , Holler and Crouch has a diagram that talks about this, and even shows what the potential does when connected through a wire(a resistor in their case). $\endgroup$ – Burak Ulgut Dec 3 '17 at 18:13
  • $\begingroup$ Really? In what page was that? I can't advance reading from the potentiometry's opening paragraphs to the second section because they didn't explain why it doesn't proceed like in a galvanic cell. $\endgroup$ – Acnologia Dec 4 '17 at 6:40

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