Operation of a Voltaic Cell

  • Thread starter zen-47
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There is something that I just can’t seem to understand about the operation of a voltaic cell. I have a question and it would be great if someone could explain to me in detail and help clear it up for me.

Let’s take for example a simple zinc and copper electrode immersed in their sulfate solutions in separate beakers. These beakers are connected by a salt bridge(NaCl or KCl).

Now why is it that zinc is able to form ions in its beaker? I know that zinc is more reactive than copper and is willing to give up electrons, but what I mean is how it is able to form ions if it is immersed in its own solution? If you were to put zinc in its sulfate solution alone separately, nothing happens (they say no reaction occurs). So why is it that in a voltaic cell, it is able to form ions?

If you were to put zinc in its own sulfate solution alone separately, is it continually forming ions with two electrons released, which in turn is taken up by the zinc ions in the sulfate solution to form back zinc again(reversible), as in Zn(s)↔Zn2+ + 2e- , therefore creating a neutral zinc metal? Same thing for copper except it is taking electrons, Cu2+ + 2e↔Cu(s)?

This is how I currently think of the operation of the voltaic cell. But I am absolutely uncertain as to whether it makes sense.

In a voltaic cell, the chloride ions in the salt bridge would neutralize the Zn2+ ions formed in the anode, unlike if zinc was alone in its sulfate solution in a beaker, where no salt bridge exists. Therefore, this leaves an excess of electrons on the zinc electrode, causing it to be negatively charged. On the copper side, the Cu2+ ions has taken two electrons from the copper electrode and caused it to be positively charged. These Cu2+ ions are then neutralized by the sodium or potassium ions in the salt bridge, therefore causing the positive charge on the copper electrode to maintain. This causes a potential difference between the two metals, causing electrons to travel from anode to cathode, and thus repeats the cycle again.

Now is this what happens in a voltaic cell? Or am I completely wrong somewhere? Another thing is, what happens when no salt bridge is connected, specifically in the anode and cathode, do any production of ions occur in the anode? Thanks..
 

Answers and Replies

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Borek
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You may assume when you put piece of metal into water it will always produce some metal ions, although their number can be extremely small. However, there are enough ions created to make the metal slightly charged (when ions go into solution, electrons are left in the bulk of the metal). Each metal is charged to different extent, so when you connect two metals there will be a potential difference - that's enough to start the process going.
 

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