[confusedstud]

Hi chemicalforums!

If I have a  copper anode with a dilute sodium chloride electrolyte, what will be oxidised and reduced? In this case, I think copper will be oxidised and also reduced as well as some hydrogen because if copper is oxidised, then it won't have a anion to balance out its charge. So if the H+ ions are given out then there will be some excess OH- that will allow the copper to form ions.  Is this correct?

While if I have a copper anode with concentrated Cl- what will happen? I'm thinking that hydrogen will form, Cl2 gas will form as well as copper will be oxidised and deposited so a lot of competing reactions will happen?  

Lastly, if I have iron anode with dilute NaCl solution what will form? I know at the cathode, copper will form but what will form ar the anode? Will copper ions be produced? Similar with concentrated NaCl.

The thing I'm confused about is when we are electroplating something with a electrolyte that has a cation which is different from the metal anode. Also  I'm confused if we have another anion besides SO4 2-although if its dilute I don't think it has any effect as OH- is already below Cl- in the ease of discharge table. And since in a SO4 2- ionic compound, and it does not have any part to play in the reaction.

Thanks for the *delete me*

[Hunter2]

A little bit confusion here.

What is your setup, what material is your anode and what is your cathode.

If your anode is copper, it will be oxidised in sodium chloride electrolyte, no chlorine development. At cathode you will get hydrogen, because sodium is not noble enough to get deposited. It doesnt matter which concentration.

If you have iron anode it will oxidised to iron-III. No copper deposition you have sodium chloride where the copper should comes from.

copper can only be deposit at cathode, if you have a copper chloride or -sulfate  electrolyte.

[vmelkon]

Hi chemicalforums!

If I have a  copper anode with a dilute sodium chloride electrolyte, what will be oxidised and reduced? In this case, I think copper will be oxidised and also reduced as well as some hydrogen because if copper is oxidised, then it won't have a anion to balance out its charge. So if the H+ ions are given out then there will be some excess OH- that will allow the copper to form ions.  Is this correct?

If you use a copper anode, I have heard that it will get covered by a mixture of oxide and chloride.
The chloride would be copper(I) chloride.
In my experience, the stuff has a blue green color, so probably some copper (II) chloride is present as well.

While if I have a copper anode with concentrated Cl- what will happen? I'm thinking that hydrogen will form, Cl2 gas will form as well as copper will be oxidised and deposited so a lot of competing reactions will happen?

Hydrogen does not form. Perhaps you meant hydrogen will form at the cathode.
The reaction is
H2O + e -> (H2O-) -> 1/2 H2 + OH-

The primary reaction at the anode is
2 Cl- + 2 e->Cl2

however, oxygen is produced as well (not sure what the equation is).
Here, I do an oxygen test
http://www.youtube.com/watch?v=6WwytVbSKUI

Lastly, if I have iron anode with dilute NaCl solution what will form? I know at the cathode, copper will form but what will form at the anode? Will copper ions be produced? Similar with concentrated NaCl.

Why would copper form at the cathode?

[confusedstud]

A little bit confusion here.

What is your setup, what material is your anode and what is your cathode.

If your anode is copper, it will be oxidised in sodium chloride electrolyte, no chlorine development. At cathode you will get hydrogen, because sodium is not noble enough to get deposited. It doesnt matter which concentration.

If you have iron anode it will oxidised to iron-III. No copper deposition you have sodium chloride where the copper should comes from.

copper can only be deposit at cathode, if you have a copper chloride or -sulfate  electrolyte.

Hi hunter2, my anode will be copper and cathode will be graphite. So if dilute NaCl is used Cu-->Cu2+ + 2e occurs at anode and 2H+ +2e-->H2 right? And no copper is deposited? What if concentrated NaCl is used? Will the same thing happen? Because now Cl- has a greater tendency to be discharged than OH- so I'm not sure if Cl- will form Cl2 or whether copper will oxidise to copper ions. And why won't the copper be deposited rather than H+ ions if the copper ions is formed in the process? Since copper is lower down in the reactivity series. Shouldn't copper be deposited in preference?

Also, if iron anode is used and cathode is graphite, with dilute NaCl solution will the results be the same? Whereby iron forms ions at the anode and hydrogen gas evolved at the cathode. Then again what would the result be if concentrated NaCl is used?

Will it be correct to say that electroplating of a material (cathode)will only occur if the cation of the electrolyte is the same metal as the anode? If not the other reactants will preferentiallly discharged than the ions formed? But then again why is this so?

[Hunter2]

Your electrolyte is NaCl in water.

On the Cathode (graphite) you will get hydrogen, sodium cannot uncharged in aqaeous solutions. 2 H⁺ + 2 e^- => H₂

On the Anode(Copper) you will get copperchloride. Copper-I is unsoluoble and will cover the anode, If acid is present also copper-II is possible. Chlorine will only developed on graphite.  Cu + Cl^- =>  CuCl +  e^- or Cu + 3 Cl^- =>  CuCl₂ +  2 e^-

In long term if enough copper-II is dissolved you will plate it on the cathode. But this takes time and the ions have to travel from anode to the cathode. For this reason elctrolytes containing the ions you want plate.

[confusedstud]

okay, then what will happen if concentrated NaCl was used with a copper anode and graphite cathode?

But why when a little copper ions are produced why can't it coat the cathode immediately? Since its lower down in the reactivity series than hydrogen.

 So can it be said that coating will only occur if the cation in the electrolyte is the same metal as the cathode?

[Borek]

So can it be said that coating will only occur if the cation in the electrolyte is the same metal as the cathode?

No. But there is no easy logic behind which metals can be electroplated on which surfaces. From what I remember copper is rather easy to be electroplated with most metals, so quite often the best approach is to plate with a copper layer first.

[confusedstud]

So can it be said that coating will only occur if the cation in the electrolyte is the same metal as the cathode?

No. But there is no easy logic behind which metals can be electroplated on which surfaces. From what I remember copper is rather easy to be electroplated with most metals, so quite often the best approach is to plate with a copper layer first.

Hi Borek, thanks for the help. So the best option I would take would be to just ignore these examples first? But now if I have an iron cathode with a Fe(iii)no3 electrolyte, will it coat my anode? Taking into considerations that I'm in my O levels this year. thanks for the *delete me*

[Borek]

In general you can't electroplate with iron in water solutions (take a look at the standard electrode potential table - hydrogen will evolve first).

[Nobby]

Its a bad example,iron is not possible at all to plate. but if you had copper nitrate it would plate.

[confusedstud]

In general you can't electroplate with iron in water solutions (take a look at the standard electrode potential table - hydrogen will evolve first).

Oh yea, that's right. But if I have a silver cathode eith a silver nitrate electrolyte, then coating will occur on the cathode right? But if another electrolyte was used like NaCl (aq)? Will there be a way to determine this just by looking at the reactivity series of metals, or is it too complicated to figure it out just like this? So in such cases, how can I tell what reaction will take place?

As for Nobby's copper nitrate electrolyte example, won't iron form iron 3 ions and copper gets reduced? why would iron be coated? Thanks for the *delete me*