Daniell cell initial equilibrium

[cianfa72]

TL;DR

About the equilibrium reached at Daniell cell electrodes without any external connection

Hello,

consider again a simple Daniell cell with salt bridge in place but no external electric connection between electrodes.

Reading from some source e.g. link1 it seems upon Zinc and Copper metal rods are dipped into their own ions solution, both will gain a negative charge (-) due to an excess of electrons gained inside themselves (metal atoms get oxidised). Having Zinc and Copper different electronegativity, the amount of electrons gained on each electrode will be not the same resulting in a potential difference voltage between them.

From other sources instead (e.g. link2), the Copper rod (Cathode) will behave the other way around: Cu++ ions reduction will take place "stealing" electrons from the Copper rod leaving it positively charged (in other words there will be a depletion of electrons inside the Copper metal rod with an unbalance between protons and electrons inside it)

Which is the truth ?

 

[mjc123]

I'm not sure we know. We can measure the potential difference between two electrodes, so if we define the potential of one electrode (0.0V for the standard hydrogen electrode), we can assign electrode potentials to other electrodes. But we can't (I think) measure the potential of a single electrode, so we don't know absolutely how positive or negative the metal is.

I don't think link 2 actually states that Cu becomes positive in the absence of an electrical connection (Cu
²⁺ is reduced when a current flows); only that Cu is more positive/less negative than Zn. Likewise link 1, at least at the beginning, talks about what happens when a metal is immersed in water (not a solution of its ions).

 

[cianfa72]

I don't think link 2 actually states that Cu becomes positive in the absence of an electrical connection (Cu
²⁺ is reduced when a current flows); only that Cu is more positive/less negative than Zn. Likewise link 1, at least at the beginning, talks about what happens when a metal is immersed in water (not a solution of its ions).

See also here link 3: for Copper osmotic pressure is greater then solution pressure thus the copper electrode will gain positive charge developing a positive potential (even though there is no current flow)