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Author Topic: Do copper or zinc electroplated iron nails go rusty?  (Read 10132 times)

Offline Falcon

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Hey i'm a grade 12 student from Australia

I am currently doing an extended experimental investiagtion on the rusting of iron...

Anyway i eletroplated 2 iron nails among several others. One with zinc and one with copper and then submerged them in salt water for a week.

I was wondering if you could help me with the chemical reactions that are occuring.

thanks


[MOD EDIT title changed to a question - Hello falcon. Please could you try to phrase your thread titles as questions, in line with our forum policy. Thanks. Chris]
« Last Edit: 13/06/2009 13:47:31 by chris »


 

Offline Chemistry4me

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Re: Do copper or zinc electroplated iron nails go rusty?
« Reply #1 on: 13/06/2009 09:43:16 »
Hi Falcon, welcome.

Hmm...think about the reactivity of the metals. The zinc will protect the iron because it's more reactive. But what about the copper? Sorry, love to stay but I got to go, but I'm sure someone will help you out. :)
What reactions do you think are occuring?
 

Offline chris

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Do copper or zinc electroplated iron nails go rusty?
« Reply #2 on: 13/06/2009 14:03:58 »
Zinc is more reactive than iron and will therefore "sacrificially" protect it. In other words the zinc will go into solution more readily than the iron: Zn → Zn2+ + 2e-

This is the basis of "galvanising" iron to stop it rusting and the way sacrificial anodes can be used to reduce the rate of corrosion on boats and bridges. In this latter example, a block of metallic zinc is bolted to the ironwork (so as to ensure a good electrical contact). The zinc will then donate electrons to the iron, or the surroundings, becoming ionised in the process, which prevents oxidation of the metallic iron.

The beauty of this approach is that you don't need to cover all of the iron with zinc - you just need to ensure a good electrical contact. In other words, even if you electroplated just half of your nail both halves would be protected.

As to copper, this is less reactive than iron. The evidence for this is that if you hold a steel (iron) key in a solution containing copper ions (Cu2+) the key becomes copper coated because the iron goes into solution producing, I believe, iron III ions, and reducing the copper ions to metallic copper in the process:

2Fe + 3Cu2+ → 3Cu + 2Fe3+ (equation correct based on the supposition that the iron adopts the iron III oxidation state).

Therefore, a copper-plated nail will not be sacrificially protected in the same way as a zinc-coated nail. 

However, although the copper may not be able to sacrificially protect the iron, if the copper coating is uniform and intact (i.e. no breaches) then it will provide chemical protection and hence corrosion resistance so long as it remains that way.

Chris
« Last Edit: 13/06/2009 14:12:52 by chris »
 

Offline Falcon

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Do copper or zinc electroplated iron nails go rusty?
« Reply #3 on: 14/06/2009 06:12:44 »
Thanks for the help so far you guys are life savers <3

however is it because the copper is less reactive the reaction between copper and water is not spontaneous so if the nail was uniformly covered there would be no reaction at all??

thanks again
 

Offline Chemistry4me

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Do copper or zinc electroplated iron nails go rusty?
« Reply #4 on: 14/06/2009 06:23:06 »
I think this site might help

http://www.practicalchemistry.org/experiments/preventing-rusting,251,EX.html

The more reactive metal, iron, donates electrons to the copper and becomes electron deficient itself. This increases the rate of the rusting.
 

Offline Falcon

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Do copper or zinc electroplated iron nails go rusty?
« Reply #5 on: 15/06/2009 10:41:37 »
thanks for the help guys,

its handed in now so fingers crossed A+
 

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Do copper or zinc electroplated iron nails go rusty?
« Reply #5 on: 15/06/2009 10:41:37 »

 

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