Ask A Scientist Chemistry Archive

name         Matthew
status       student
age          15

Question -   I'm a freshman in high school. I've been trying for
about a week looking at libraries and other places to find information
about my question, unsuccessfully. My question is how and why does salt
and water speed up corrosion on metal objects? I have tried the sites you
gave me on my last question but they did not have what I was looking for.
I have tried looking at the archives, http:///www.google.com
http://www.altavista.com/sites/search/simage
http://www.glenbrook.k12.il.us/gbn/imc/ and the others you gave me.
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Matthew,

Let me address the problem by referencing the rusting of iron. When iron
rusts (oxidizes), it surrenders electrons to oxygen to form iron oxide. If
the electrons cannot be transferred from iron to oxygen, oxidation cannot
occur. When dry iron is exposed to dry oxygen gas at room temperature,
oxidation is rather slow because there is little opportunity for the
electrons to flow from the metal to oxygen.

Pure water is a rather poor conductor of electricity. However, it's a better
conductor than dry air. If the water is contaminated with salt, it becomes
an excellent conductor. As a result. iron exposed to salty water oxidizes
much faster that it would if exposed to either dry air or pure water.

Regards,
ProfHoff 398
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