From: ROY MAYEDA (roymayeda@yahoo.com)
Date: Thu Oct 17 2002 - 19:08:49 PDT
Message-ID: <20021018020849.35231.qmail@web20413.mail.yahoo.com> Date: Thu, 17 Oct 2002 19:08:49 -0700 (PDT) From: ROY MAYEDA <roymayeda@yahoo.com> Subject: Re: Burners and/or Torches
Hi Charlotte.
A couple of problems.
(1) The salt may or may not melt. Whether it does or
not, the melting of the sugar does not show that
covalent bonds are weaker (as you don't have to break
any of them to melt the sugar), but rather that
molecular solids tend to have weaker attractions
between molecules than ionic solids have between their
ions.
(2) Hopefully you're thinking of melting the pennies
rather than "burning" them. (Students commonly misuse
the term "burn" to mean anything to do with heating in
a flame.) A couple of cautions about this. The first
is that the fumes given off by zinc that is actually
hot enough to burn are toxic and must be avoided.
Secondly, if you simply want to melt the core out of a
post-1982 penny, be sure to score the edges in several
spots or all the way around to keep the molten zinc
from spurting out under pressure. If you simply want
to get the cool hollow penny thing going, we've done
the trick of dissolving the core out of the post-'82's
at TI workshops by scraping the edges in several spots
and soaking them in any acid-containing toilet cleaner
for a while. Also remember that the pre-1982 pennies
are a solid copper-zinc alloy (95/5 if I remember
correctly), the post-1982's are a zinc (alloy?) core
clad with pure copper. The 1982's are mixed as the
change was made during that year.
As far as torches, most hardware stores should have
them. If you can get one with a little stand to hold
it, that would be recommended. As with all demo's,
practice beforehand, and be sure to use either a
shield or have all observers (as well as the
demonstrator) wear appropriate safety gear -- goggles,
etc. Have fun. Play safe.
Roy Mayeda
Sauk Centre HS
Sauk Centre, MN
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