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Topic: Redox inside a battery  (Read 335 times)

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Offline Marcos Castillo

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Redox inside a battery
« on: April 23, 2020, 12:34:00 PM »
Hello
I've got a paragraph, and a question about it. I write it down and then my attempts to solve them:
"The standard alkaline battery uses Zn and MnO2. KOH separates them. OH- ions react with Zn electrode to produce Zn(OH)2 and free electrons. These electrons move trough a electrical circuit to return to the MnO2 electrode, where they react, to produce MnO3 and OH- ions. Both these quemical reactions end up producing a difference in potential voltage about 1,5 V between both electrodes."
My attempt to translate this into quemichal formulas:
Zn+2OH- :rarrow:Zn(OH)2+2e-
MnO2+2e- :rarrow:MnO3+OH-
How do I balance second reaction, MnO2+2e- :rarrow:MnO3+OH-?
Thanks

Offline chenbeier

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Re: Redox inside a battery
« Reply #1 on: April 23, 2020, 12:47:26 PM »
It is not MnO3, it will be Mn3+

The reaction is MnO2 + H2O + e- => MnOOH + OH-

Offline Marcos Castillo

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Re: Redox inside a battery
« Reply #2 on: April 23, 2020, 09:45:04 PM »
Hello chenbeier

It is not MnO3, it will be Mn3+

The reaction is MnO2 + H2O + e- => MnOOH + OH-

It is not needed an equilibrium in electrons?. I mean that 2 electrons are released, and only one needed:

Zn+ 2OH-=>ZnO+H2O+e-

MnO2 + H2O + e-=> MnOOH + OH-

Which is the role played by KOH? Where does it takes part?

« Last Edit: April 23, 2020, 10:24:56 PM by Marcos Castillo »

Offline chenbeier

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Re: Redox inside a battery
« Reply #3 on: April 24, 2020, 07:02:21 AM »
Of course you need balance the equation, in his way that you can eliminate the electrons.

OH- is needed to complex the zinc.

Offline Marcos Castillo

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Re: Redox inside a battery
« Reply #4 on: April 24, 2020, 10:51:58 AM »
I think it's only needed to multiply per two the reduction reaction of the manganese, and then sum both semireactions:

1-Zn+2OH-=>Zn(OH)2+2e-
  MnO2+H2O+e-=>MnOOH+OH-

2-Zn+2OH-=>Zn(OH)2+2e-
  2MnO2+2H2O+2e-=>2MnOOH+2OH-

3-Zn+2OH-=>Zn(OH)2+2e-
  2MnO2+2H2O+2e-=>2MnOOH+2OH-

4-Zn+2MnO2+2H2O=>Zn(OH)2+2MnOOH
 

Offline chenbeier

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Re: Redox inside a battery
« Reply #5 on: April 24, 2020, 11:32:51 AM »
Yes correct. Zink stays as a complex Zn(OH)4]2- normally.

Offline Marcos Castillo

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Re: Redox inside a battery
« Reply #6 on: April 24, 2020, 03:42:22 PM »
Thanks!

Offline AWK

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Re: Redox inside a battery
« Reply #7 on: April 26, 2020, 06:25:14 AM »
Yes correct. Zink stays as a complex [Zn(OH)4]2- normally.

A bit incorrect, but you can guess this printing error.
AWK

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