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Topic: galvanic reaction between zinc and copper in electrolyte.  (Read 6544 times)

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Offline xchcui

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galvanic reaction between zinc and copper in electrolyte.
« on: June 08, 2015, 11:07:11 AM »
Hello.

I read that when you dip into electrolyte metals,the metals tend to drop atoms into the electrolyte as positive ions.But when i read about the action in H2SO4 electrolye ,when one metal is zinc and the other is copper,it says that zinc atoms drop into the solution as positive ions,but nothing is mentioned about the copper electrode.Does the copper electrode also drop copper atoms as positive ion into the solution?(before a wire connected between them)?
and if it doesn't,why it doesn't,while the zinc does?

It only said that,when we connected the electrodes with a wire the electrones flow from the zinc to the copper through the wire,the H+ move to the copper electrode and become hydrogen gas and the SO4-- connected to the zinc and become ZNSO4 in the solution,while the zinc electrode decrease.

Thanks in advance.

Offline Enthalpy

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Re: galvanic reaction between zinc and copper in electrolyte.
« Reply #1 on: June 08, 2015, 01:21:51 PM »
This relates (but not fully) to the difficulty to take electrons from the metal. Your acid (H2SO4) has H+ ions dissolved in water, and these H+ take an electron from metals to get neutral themselves, thereby dissolving the metal as ions - but only if this is easy enough.

Because this case has practical importance, the "difficulty to rip electrons compared to hydrogen" is formalized as the "standard electrode potential" and tables exist
http://en.wikipedia.org/wiki/Table_of_standard_electrode_potentials
from which you see that copper has a positive potential and shouldn't react with the acid (err, that's approximative) while zinc has a clear negative potential and does react.

Well, it can become less simple, for instance titanium and tantalum have a negative potential but their oxide layer protects them often, and this is about impossible to predict ex nihilo.

Offline Borek

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Re: galvanic reaction between zinc and copper in electrolyte.
« Reply #2 on: June 08, 2015, 04:34:47 PM »
Have you heard about reactivity series?
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Offline xchcui

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Re: galvanic reaction between zinc and copper in electrolyte.
« Reply #3 on: June 10, 2015, 08:06:26 AM »
Yes,i have heard about reactivity series and i know that the metal that is more negative(zinc is negative compare to copper) is the active one which loses Zinc atoms,but i know that this is happens when you connect a wire between them(then the action begins).
I am asking about what happens before the wire connections?
I read that if you dip a metal into solution,the metal tend to lose some atoms that drop into the solution as cations until there is a kind of equilibrium.It wasn't mention that The H+ or somthing else caused to that action.it says that this is what metal tend to do in elecrolyte,unless i connect a wire between them and then the H+ takes electrons from the copper.
So i wonder,if metals tend to lost atoms in the electrolyte as the zinc did,why doesn't the copper loses atoms as cations into the electrolyte until equilibrium?and i mean before connecting the wire.
If the H+ ions(in the solution) are the reason for the zinc atoms to drop into the electrolyte as positive ions,BEFORE CONNECTING THE WIRE,i might understand your rest explanation about the reason why the copper doesn't behave like the zinc and i assume that if i dip into the solution only the copper(without the zinc)it will also release some atoms as positive ions until equilibrium.
What am i missing here?

Offline Enthalpy

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Re: galvanic reaction between zinc and copper in electrolyte.
« Reply #4 on: June 10, 2015, 12:21:19 PM »
Most people would be happy with "copper releases no ions because it's less ionizable than hydrogen", but if you want to think it as an equilibrium, replace "no ions" by "few ions". "Few" coming from the positive potential.

Offline Borek

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Re: galvanic reaction between zinc and copper in electrolyte.
« Reply #5 on: June 10, 2015, 01:11:53 PM »
You are wrong about this part :

i know that this is happens when you connect a wire between them(then the action begins).
I am asking about what happens before the wire connections?

Zinc is so reactive it will react - albeit slowly - with H+ that are always present in water. This is a reason why hydrogen (despite not being a metal) is present in the reactivity series.
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Offline xchcui

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Re: galvanic reaction between zinc and copper in electrolyte.
« Reply #6 on: June 10, 2015, 01:44:54 PM »
Ok.
So the phrase"metal tend to release positive ions in electrolyte"is seems to be right,only that the more active metal tend to release more positive ions.
But i didn't understood:Do the metals release positive ion,because of the H+ in the electrolyte?
My confusion is due to the reason that i read:
"metals tend to release ion to the electrolyte until getting into equilibrium".
it didn't mentioned what is the reason.
Do the H+ response for that?(from your explanation it seems that it is,but i am not sure what did you refer to)
I would like to mention that i am talking about the situation that the two metals are in the electrolyte without any exterior wire for the electrons to flow.

Offline xchcui

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Re: galvanic reaction between zinc and copper in electrolyte.
« Reply #7 on: June 12, 2015, 01:58:27 AM »
Thank you for your responses,but why don't you answer directly to my question?
Do the metals release positive ion,because of the H+ in the electrolyte?(before wire is connected/galvanic action).This question is the main topic.
I have been repeated about this question 3 times with no directly answer.
I will very appreciate if you focus on this question.

Offline billnotgatez

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Re: galvanic reaction between zinc and copper in electrolyte.
« Reply #8 on: June 12, 2015, 03:21:20 AM »
Quote
Thank you for your responses,but why don't you answer directly to my question?
@xchcui
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Offline xchcui

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Re: galvanic reaction between zinc and copper in electrolyte.
« Reply #9 on: June 13, 2015, 05:23:41 AM »
OK. my mistake.
I didn't read that,but now i understand that the members followed the rules and answered to my question indirectly.
I read their answer,i thought about that and it seems that the answer is that the H+ ions are responsible for the metals to release positive ions into the solution until equilibrium(then stops).And that before connecting any exterior wire between the metals.
So,now i think that this is the answer by the indirectly answers that they gave me(Socratic Method).Now i need only approval,that it is right.

Offline xchcui

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Re: galvanic reaction between zinc and copper in electrolyte.
« Reply #10 on: June 15, 2015, 09:10:51 AM »
Even though you said that the people who ask the questions should understand the answer by the member's indirect answer.you should,eventually,confirm if the conclusion that he has been reached,is right.

How should i know if i am right or not? ???

Offline Borek

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Re: galvanic reaction between zinc and copper in electrolyte.
« Reply #11 on: June 15, 2015, 09:53:26 AM »
Do the metals release positive ion,because of the H+ in the electrolyte?(before wire is connected/galvanic action).

Some do, some don't. That's why I have pointed you to the reactivity series.

Generally speaking - for the potential to exist, you need charge separation. If you see two objects and there is a potential difference between them, that means they are differently charged (this is very basic physics). So if you see two electrodes put into the solution, and there is a potential difference, they must be charged. The only way for a piece of metal to become charged if is some of the metal dissolves, leaving excess electrons on the electrode.

In the case of zinc situation is slightly different, as the electrons produced during the dissolution and up in the gaseous hydrogen. But the electrode is still charged for the same reason, just the amount of charge (potential of the electrode) is high enough to reduce H+.
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Offline xchcui

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Re: galvanic reaction between zinc and copper in electrolyte.
« Reply #12 on: June 16, 2015, 09:50:27 AM »
Thanks.
That question had been asked in order to understand my main issue about galvanic action in car coolant.
But since it is a different issue i am going to open a new thread.

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