How cathode is positively charged in voltaic cell?

[gracy]

How cathode is positively charged in voltaic cell?I mean at cathode reduction takes place ,but the electron which is gained for reduction comes from anode,than why cathode becomes positively charged ?As electrons are from anode not from cathode that means electrons are not lost by cathode ,so it should not become positively charged.Right?

 

[proton007007]

cathode is said to be the positive electrode . its not positively charged . everything in nature is electrically neutral . we perceive it as separate charges for better understanding .

 

[bwana]

cathode is said to be the positive electrode . its not positively charged . everything in nature is electrically neutral . we perceive it as separate charges for better understanding .

Alright, this might be off topic BUT, I too am perplexed by the phenomenon of radioactive decay. How is electrical neutrality maintained when electrons (beta particles) and proton-neutron sets (alpha particles) are being spit out by some elements. These particles are whizzing by all the other neutral particles - how do they maintaintain their neutrality.

 

[Drakkith]

cathode is said to be the positive electrode . its not positively charged . everything in nature is electrically neutral . we perceive it as separate charges for better understanding .

I'm sorry but this is just wrong.

Alright, this might be off topic BUT, I too am perplexed by the phenomenon of radioactive decay. How is electrical neutrality maintained when electrons (beta particles) and proton-neutron sets (alpha particles) are being spit out by some elements. These particles are whizzing by all the other neutral particles - how do they maintaintain their neutrality.

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.

How cathode is positively charged in voltaic cell?I mean at cathode reduction takes place ,but the electron which is gained for reduction comes from anode,than why cathode becomes positively charged ?As electrons are from anode not from cathode that means electrons are not lost by cathode ,so it should not become positively charged.Right?

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.

 

[Bystander]

cathode is positively charged in voltaic cell?

"Cathode" is the term for any electron source. "Electrodes" in a voltaic cell can be "cathodes" when one considers their function within the cell as electron sources for reactants within the cell, and as "anodes" when one considers their function outside the cell as electron sinks for an electrical circuit.

 

[Drakkith]

Indeed. A cathode is generally the electrode that conventional current leaves. Conventional current is a flow of positive charges, which is the same as negative charges flowing the opposite direction. So the cathode is just the electrode that electrons flow into. This refers to the external circuit of course. For a battery, the 'internal circuit', consisting of the two electrodes and electrolyte, this is opposite. Electrons leave the cathode and flow into the electrolyte.

 

[gracy]

Can you please tell me why cathode is at high potential in galvanic cell?As in galvanic cell electrons naturally(spontaneously) flow from anode to cathode ,cathode must be at higher potential because electrons always move from lower to higher potential.But how cathode is at higher potential?How anything can be at higher potential?

 

[Bystander]

As in galvanic cell electrons naturally(spontaneously) flow from anode to cathode

Very quick question: has there been any explicit statement in class regarding electrode name convention? There are at least two, European, and American, and they have been a source of endless confusion over the past one or two centuries.

A cathode is generally the electrode that conventional current leaves.

Same question: which convention?

 

[gracy]

We have been told that at anode oxidation takes place and at cathode reduction takes place.I don't know whether it is European and American convention.Please tell me why cathode is at high potential in galvanic cell?How anything can be at higher potential?

 

[Bystander]

cathode reduction takes place.

I'll call that American. It's an electron source and reduces oxidized species which reach it.

at higher potential?

Without context, "higher potential" is meaningless; the discussion in your text or lecture notes has to be comparing it to something, and without knowing what that "something" is, it's tough to really answer your question.

 

[gracy]

Without context, "higher potential" is meaningless

Higher potential than anode.

 

[Bystander]

This may be more in reference to the electrons themselves. Electrons at/on the cathode have a higher potential energy than exists for oxidized species approaching the cathode, or at the anode once they've been transported through the cell.

 

[gracy]

. Electrons at/on the cathode have a higher potential energy

You mean it depends on material of cathode or anode?If one electrode is made up of copper and the other one is made up of zinc,electrons of zinc would be at lower potential than electrons of copper?Right?If yes.then it implies that reduction or oxidation potential is all about electrons of particular material/element.

 

[Bystander]

depends on material of cathode or anode?

Yes.

copper and the other one is made up of zinc

Copper ions oxidize zinc, or zinc reduces copper ions.

reduction or oxidation potential is all about electrons of particular material/element.

Yes.

 

[gracy]

Sir,last question
If any element's electron has greater oxidation potential does it mean it has lower potential than the electrons of cathode?But why only reduction potential is considered as potential not oxidation potential?Because if we consider oxidation potential the anode would be at higher potential.

 

[Bystander]

reduction potential is considered as potential not oxidation potential?

This is another of those "arbitrary choices/conventions." Whether it's regarded as one or the other, it's the same reaction. We're just looking at which direction we're going to consider. If we say "oxidation," it means we're going to look at how easily every reaction proceeds as an oxidation when comparing them. If we say "reduction," we're comparing every reaction as a reduction.

 

[gracy]

This is another of those "arbitrary choices/conventions." Whether it's regarded as one or the other, it's the same reaction.

Let us take oxidation potential as potential .Then anode (at which oxidation takes place)should be at higher potential than cathode.As electrons move towards higher potential ,electrons should move from cathode to anode,but it is really not the case.So how it's our choice whether we take oxidation or reduction potential as potential of electron?

 

[gracy]

How does a salt bridge complete circuit?As no electrons flow within salt bridge.

 

[Borek]

Current is a movement of charge. Electrons are not the only charged objects.

 

[gracy]

So ,you mean ions ?Ions are responsible for completing the circuit via salt bridge?

 

[Borek]

Yes.

 

[gracy]

But to complete the circuit ions/electrons should move from cathode to anode ,how that occurs?

 

[Borek]

Through an external circuit.

 

[gracy]

an external circuit.

In which load is attached,right?

 

[Borek]

Yes.

 

[DrDu]

Maybe it is important to note that charge carriers do not only move due to electric fields and potentials but also because of,e.g., density gradients and, more generally, due to gadients of the chemical potential.

 

[epenguin]

Maybe it is important to note that charge carriers do not only move due to electric fields and potentials but also because of,e.g., density gradients and, more generally, due to gadients of the chemical potential.

Yes I had occasion recently to remark about this in connection with batteries, and also that something can seem to move against a gradient, a guy, not a student, seemed to be getting into a slight tangle about it.
Solubility and Precipitation of Unknown Ion

I think, well does anyone agree? - that quite a lot of harm is done by teaching electrochemistry as ions being attracted to the electrode of opposite sign like electrostatic attraction in vacuum. You can explain electrochemistry without saying that. All that happens is chemical reactions - but by the 'miracle' of metallic conduction a reaction in one place can be coupled to another in another place. The reactions cause concentration gradients, thence net ion movements. (Actually I think it would be possible to develop the whole subject without using the concept 'electrical potential' )

Once implanted this idea of attraction at a distance is hard to shake off. In fact I'm not sure I can explainl
band electrophoresis now any other way.

 

[gracy]

In which load is attached,right?

Yes.

In external circuit electrons move from anode to cathode,I am asking where do electrons go after reaching cathode? To complete the circuit ions/electrons should move from cathode to anode,that's what I am asking ,how that occurs?

 

[DrDu]

In external circuit electrons move from anode to cathode,I am asking where do electrons go after reaching cathode? To complete the circuit ions/electrons should move from cathode to anode,that's what I am asking ,how that occurs?

They react with the ions of the solution, e.g. ##\mathrm{Cu^++e^- \to Cu}##.
Let's consider the simple example of raffination of copper. There you have two electrodes, the anode consisting of impure copper and a pure copper cathode.
On the anode, copper dissolves according to ## \mathrm{Cu \to Cu^+ +e^-}##.
The electrons will be driven by an external electric field through a wire and e.g. a generator to the cathode, where the reverse reaction takes place and pure copper is deposited. Hence on the anode copper ions are created and on the cathode destroyed.
This generates a concentration gradient which drives the copper ions to the cathode.
Hence the copper ions transport the current in the solution. The gradient of the copper ion concentration is equalled by a static gradient of the counter ions which don't move, so that the solution remains overall charge neutral.

 

[gracy]

Yes.But that doesn't complete the circuit.To complete the circuit negative ions/electrons should go to anode.That's where salt bridge comes in.I think it all works in this manner
Electrons are lost by anode ,they move from external circuit to cathode.And those electrons are gained by cations of cathode half cell and get deposited on cathode.But to complete the circuit which is essential for flow of current the anion from cathode moves through the salt bridge into anode half cell .,this is how circuit is completed.Salt bridge contains inert electrolytes which provide conducting medium for flow of ions without reacting with them.

 

[DrDu]

Yes, if you have a salt bridge, both cations and anions will contribute to the current. The precise extent of current carried by anions and cations depends on their respective mobility.

 

[gracy]

Yes, if you have a salt bridge, both cations and anions will contribute to the current. The precise extent of current carried by anions and cations depends on their respective mobility.

You mean as we have studied protons do not produce current but electrons do,is it not true for ions?I mean do cations also produce current?What's the direction of the current produced by ions?In the direction of anions flow or cations flow?

 

[DrDu]

Who sais that protons don't carry current? In solution, protons have the highest mobility of all charge carriers. Anions moving in the same direction as electrons will prduce a current of the same sign, while cations moving in the same direction as electrons will produce a current in the other direction. In a salt bridge, anions and cations move in different directions (anions moving to the + pole, cations to the - pole), hence the sign of the current carried by them is the same.

 

[gracy]

Who sais that protons don't carry current?

In our class we have been told that it was a misconception that flow of proton produces current it was later learned but convention was not changed so still current direction is indicated by direction of proton (opposite of direction of flow of electrons).

 

[DrDu]

At the time the direction of current and the + and - were fixed, people had no idea about the existence of electrons and protons. So nobody ever claimed that the current in a wire were due to protons. Anyhow, that the current in a wire is carried by electrons does not mean that cations can't move (and can be the main charge carriers) in other media.