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Topic: how do Sacrificial electrodes work? (edited)  (Read 2688 times)

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Offline iScience

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how do Sacrificial electrodes work? (edited)
« on: March 18, 2015, 06:13:49 PM »
EDIT: i decided to just rewrite the whole question..

i have brass metal in contact with ammonia(liq), could  someone help me identify the oxidation reaction?

i thought the oxidation rxn was supposed to involve the ammonia and the copper, but that combination would lead to the copper being reduced, not oxidized. am i right?
how exactly is copper losing its electrons?
« Last Edit: March 18, 2015, 07:17:00 PM by iScience »

Offline Borek

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Re: how do Sacrificial electrodes work? (edited)
« Reply #1 on: March 18, 2015, 07:38:16 PM »
Why do you think copper gets oxidized?
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Offline unsu

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Re: how do Sacrificial electrodes work? (edited)
« Reply #2 on: March 19, 2015, 10:31:04 PM »
Quote
i thought the oxidation rxn was supposed to involve the ammonia and the copper, but that combination would lead to the copper being reduced, not oxidized. am i right?

sorry I do not understand anything you are talking about  :)

Offline thelastone

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Re: how do Sacrificial electrodes work? (edited)
« Reply #3 on: March 20, 2015, 12:42:25 PM »
I think to recall that anhydrous ammonia doesn't react with Copper or Zinc alone, BUT when there's humidity forms a very stable ammonia complex (Cu(NH3)6)2+.

Hope it helps.

Offline john13579

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Re: how do Sacrificial electrodes work? (edited)
« Reply #4 on: May 09, 2015, 11:09:04 AM »
The copper is indeed oxidized to copper(II).
Copper reacts readily with aqueous ammonia in the presence of oxygen, as follows:
Cu+ 1/2 O2 + 4NH3(aq)  :rarrow: Cu(NH3)42+ + 2 OH-

The reaction only works in presence of oxygen as the oxidizing agent (http://jes.ecsdl.org/content/100/10/421.short)

ammonia serves to form the Tetraamminecopper(II)  ion and remove the protective oxide layer form the surface of the metal allowing for further oxidation.

It is referred to as season cracking (http://en.wikipedia.org/wiki/Season_cracking)

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