How cathode is positively charged in voltaic cell?

[gracy]

Is my 48th post,correct?

 

[gracy]

Salt bridges are used in laboratory applications, that is for cells that do no electrical work, nor have any electrical work done on them. One might be interested in comparing the concentrations of two different solutions of ferrous sulfate, for example, and it is necessary to prevent the solutions from mixing over the time frame of the measurement. Mixing is prevented by use of the salt bridge which allows for ionic current from a solution in one half cell (Fe/Fe+2) at one concentration to the second half cell (Fe/Fe+2) at a different concentration without the two solutions mixing or diffusing into one another and reducing the potential difference between the two half cells to zero before the measurement can be accomplished. Check the index in the textbook for "concentration cells."

But according to the video I have seen on concentration cell ,electrons are transferred not the ions.This is the video i am talking about

 

[gracy]

Mixing is prevented by use of the salt bridge which allows for ionic current from a solution in one half cell (Fe/Fe+2) at one concentration to the second half cell (Fe/Fe+2) at a different concentration without the two solutions mixing or diffusing into one another

What is mixing of solutions then?I thought that if ions of one half cell travel to second half cell ,it is said that solutions are mixed.

 

[Bystander]

,electrons are transferred not the ions.

This is in the external circuit. The part of the circuit where chemistry is happening carries current in one, or both, directions by ion transport.

Both of the processes will occur simultaneously ,the one i have mentioned in first option is to complete the circuit, and the second one to maintain neutrality ,right?

Yes.

I thought that if ions of one half cell travel to second half cell ,it is said that solutions are mixed.

Any transfer of solute, ions, solvent, from one half cell to the other is "mixing." The idea behind the salt bridge is that the ion transfer is insignificant over the course of a measurement due to difficulty of diffusion through the salt bridge, or that the actual ion transport carrying the current involves the ions of the salt bridge, and that the salt be chosen to minimally interfere with the chemistry being measured/studied.

 

[gracy]

The idea behind the salt bridge is that the ion transfer is insignificant over the course of a measurement due to difficulty of diffusion through the salt bridge,

Only sufficient enough to complete the circuit?

 

[Bystander]

sufficient enough to complete the circuit?

Yes.

 

[gracy]

that the actual ion transport carrying the current involves the ions of the salt bridge,

Ions of salt bridge also produce current?I thought they are only to maintain neutrality .

 

[Bystander]

Ions of salt bridge also produce carry current?

For every cation reduced at the cathode, to maintain neutrality, cation(s) must move through the salt bridge (carrying charge/current).

 

[gracy]

For every cation reduced at the cathode, to maintain neutrality, cation(s) must move through the salt bridge (carrying charge/current).

But at the same time For every anion oxidized at the anode, to maintain neutrality, anions must move through the salt bridge (carrying charge/current)Won't it cancel the current produced by cations of salt bridge?

 

[Bystander]

Won't it cancel the current produced by cations of salt bridge?

The two contributions are NOT necessarily equal. If you look at current through a Cu/Cu⁺²//Cu⁺²/Cu cell for refining/producing electrolytic copper, almost all the current carried through the cell is by Cu⁺² ions. There is very little transport by SO₄^-2 ions which more or less maintain the electrical neutrality by playing "hot potato" or passing Cu⁺² ions from one to another.

 

[proton007007]

I'm sorry but this is just wrong.
They don't. Electrons have a negative charge, protons have a positive charge, and neutrons are electrically neutral. You're replying to a bad answer.
The electrons that flow into the cathode are used in the chemical reaction between the cathode and the electrolyte. They are indeed 'lost' from the cathode in this reaction.

What I actually meant was that the electrons that reach at the electrode get consumed and the negative charge doesn't linger on . In totality , everything is neutral . The electrolytic cell in whole is neutral . The cathode is not charged but as you said , the action of loss of electron makes us call it positive electrode .

 

[Borek]

The cathode is not charged

It is. If it wasn't charged there would be no potential difference between cathode and anode.

Charge is typically pretty small, but it definitely is there.