Voltaic Cell

I studied that in the above setup electrons are attracted by Cu because of their reduction potential but they don't involve in reaction because of the d-bands of the electronic structure so Hydrogen accepts the electron and become as Hydrogen gas

My question is why don't the H+ ions absorb electrons near the Zinc strip itself, why the electrons are travelling through the external load to combine with H+ on the other electrode instead of combining to them at the Zinc strip itself

If the above scenario is impossible to happen How the H+ ions are combining with released electrons near the Zinc strip in the Activity of putting a Zinc strip inside a beaker with dilute sulphuric acid

I would also like to know why this is not as popular as Salt bridge experiment (Is this an inefficient way of producing electricity?) I was unable to find much resources on these kind of setups(Without salt bridge) on the internet.

Please correct me If I made any silly mistakes ;)
There is a similar Question regarding the electrolysis process but I had some uncleared doubts

  • $\begingroup$ Please provide reason for downoting! $\endgroup$ – Siva Manasan Dec 1 '18 at 16:21

Changing a few words may make the situation clearer. There are three reactants: 1) Zn, 2)Cu and 3) H2SO4. Actually, the Cu does not change, so it is not really a reactant, but it is part of the overall reaction.

What happens when Zn is placed into acid: some Zn atoms dissolve to become Zn++ ions, and they leave their electrons behind, so the Zn electrode become negatively charged. H+ ions may be attracted to the electrode, but there are barriers to formation of H2...too complicated for a simple discussion. But if you lead the electrons to a different electrode (like Cu), H+ ions can come closer to the electrode, and more easily form H2 molecules which will rise to the surface of the solution. I would say not that electrons are attracted to the Cu, but rather that they are forced there by the negative voltage developing on the Zn.

Why don't the electrons combine with H+ near the zinc strip? Zinc (especially pure zinc) is said to have a high hydrogen overvoltage. This means essentially that H2 is not formed and evolved as easily as theory suggests; it could be that a monolayer of hydrogen is deposited, but is stuck to the Zn surface as atoms which do not combine to H2 easily - you have to force them by forcing on more H+ ions. And hydrogen evolution eventually happens even with ordinary zinc because there are always tiny imperfections in the surface which can more easily permit 2 H atoms to combine to H2. In past days, a very thin surface coating of mercury was applied to zinc electrodes in order to coat these surface imperfections and reduce the ability of the zinc to evolve H2.

Perhaps the Salt Bridge experiment is a way to more clearly separate the two reactions of Zn dissolution and H2 evolution. In real batteries, salt bridges are not used. They would give extra resistance to current flow and reduce energy output.

  • $\begingroup$ The answer was really helpful but regarding the "but there are barriers to formation of H2...too complicated for a simple discussion.", Can you provide any external links(Wikipedia,etc.) for further understanding/reference, Thank You so much. $\endgroup$ – Siva Manasan Nov 29 '18 at 16:25
  • $\begingroup$ One (short) article is: en.wikipedia.org/wiki/Overpotential ; a longer one is: en.wikipedia.org/wiki/Electrochemistry . There are lots of term in both articles that you can Google to get more information. In a way, it is simple, but it is complex because every element has its own peculiarities that need to be explained by different mechanisms. Do a little at a time, try to understand one system at a time; eventually you will understand it all. (Not that I do...) BTW, overvoltage and overpotential can be used interchangeably if you want to. $\endgroup$ – James Gaidis Nov 30 '18 at 16:46

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