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Topic: Electrochemistry: Corrosion  (Read 9483 times)

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777888

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Electrochemistry: Corrosion
« on: October 30, 2004, 06:26:59 PM »
1)In dry air, small quantities of H2S(g) can slowly react with Ag to produce H2(g) and Ag2S. Using the knowledge of riting and balancing redox equations, write and label the half-reaction and net ionic equations:

-This is a question quite different from other questions in the section. How can I write a half-reaction and net ionic equation? I don't understand...

2)When rusting appears on a car body, it appears around the break or chip in the paint but the damage may extend under the painted surface for some distance.
a)What is the evidence for damage extending well beyond the break in the paint.
b)Explain why the damage may extend far from the break in the paint.

These are the only 2 questions that I don't get. I spend hours reading the section in my textbook but I can't get the answer! Please teach me! I would appreciate!

Demotivator

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Re:Electrochemistry: Corrosion
« Reply #1 on: October 30, 2004, 07:55:18 PM »
1) Maybe it's mistyped?
 I suppose it means writing the two half reactions, and adding them to get the net, but leaving the S out since S does not change it's oxidation state. So instead of Ag2S, just 2Ag+.

777888

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Re:Electrochemistry: Corrosion
« Reply #2 on: October 30, 2004, 09:30:05 PM »
I think I get it!
2H+ + 2e -> H2
2Ag -> 2Ag+ +2e

Net equation: 2H+ +2Ag -> H2+2Ag


How about question 2, can anyone teach me? Thanks :)

Demotivator

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Re:Electrochemistry: Corrosion
« Reply #3 on: October 30, 2004, 11:17:53 PM »
2 a)  Evidence for damage deeper than the break can be detected by a loss of magnetism of oxidized steel (test with a magnet).

b) Oxide that forms on the surface can migrate or diffuse to deeper layers of iron because the concentration gradient is the driving force.
It's like osmosis, using a liquid phase analogy.

777888

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Re:Electrochemistry: Corrosion
« Reply #4 on: October 31, 2004, 01:56:20 AM »
I don't quite understand, but thanks anyway...
« Last Edit: October 31, 2004, 01:57:16 AM by 777888 »

777888

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Re:Electrochemistry: Corrosion
« Reply #5 on: October 31, 2004, 01:13:48 AM »
Is there a difference between the terms "rusting" and "corrosion"?

ssssss

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Re:Electrochemistry: Corrosion
« Reply #6 on: October 31, 2004, 03:21:29 AM »
Is there a difference between the terms "rusting" and "corrosion"?

Corrision is the change of metal to undesirable form by the action of O2 and Moisture.I think rusting is a corrosion.But wait for more appropriate replies.

Offline Donaldson Tan

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Re:Electrochemistry: Corrosion
« Reply #7 on: November 01, 2004, 08:14:57 PM »
rusting specifically refers to iron
"Say you're in a [chemical] plant and there's a snake on the floor. What are you going to do? Call a consultant? Get a meeting together to talk about which color is the snake? Employees should do one thing: walk over there and you step on the friggin� snake." - Jean-Pierre Garnier, CEO of Glaxosmithkline, June 2006

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