zinc pennies in HCl

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From: Charlotte Lum (charjinglum@yahoo.com)
Date: Wed Dec 11 2002 - 06:25:08 PST 

Message-ID: <20021211142508.78428.qmail@web40710.mail.yahoo.com>
Date: Wed, 11 Dec 2002 06:25:08 -0800 (PST)
From: Charlotte Lum <charjinglum@yahoo.com>
Subject: zinc pennies in HCl

As an introduction to chemical reactions, my class scored post-1983
pennies so that the zinc was exposed, and let them sit in Lysol
toilet bowl cleaner (hydrochloric acid). Zn + 2HCl --> ZnCl2 + H2

There is a lot of white foam that forms within 5-10 minutes, and in
most cases it smells like rotten eggs. After a day, the pennies are
almost hollow and a black precipitate has formed.

I know that the black precipitate is zinc chloride. I would have
thought that the foam was H2 gas, but I can't explain why it formed
so quickly and smells so bad. Does it have to do with the cleaning
of the dirt on the pennies [some were quite dirty]?

Thanks,
Charlotte

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