From: ROY MAYEDA (roymayeda@yahoo.com)
Date: Mon Feb 07 2005 - 14:10:14 PST
Message-ID: <20050207221015.65733.qmail@web20422.mail.yahoo.com> Date: Mon, 7 Feb 2005 14:10:14 -0800 (PST) From: ROY MAYEDA <roymayeda@yahoo.com> Subject: Re: pinhole chemical precipitate
Hi all.
Yes, calcium chloride IS often sold in areas where
iced sidewalks are a problem! Usually it’s a mix of
various chlorides (MgCl2, CaCl2, etc.). If you’re not
really picky about what precipitates, you should be
able to get away with washing soda (sodium carbonate
decahydrate, Na2CO3•10H2O) and Epsom salts (magnesium
sulfate heptahydrate, MgSO4•7H2O). The CRC manual
lists washing soda’s solubility (all solubilities
given as grams solute/100 ml H2O) as ranging from 21.5
to 421 between 0 and 104 C. (I’m assuming the higher
temp is given due to BP elevation of the solution.)
The Epsom salts’ solubilities were listed from 71 to
91 between 20 and 40 C. These should exchange and
yield sodium sulfate and magnesium carbonate. The
magnesium carbonate is nearly insoluble -- all forms
listed solubilities at less than 0.4 in hot water,
even less in cold. The sodium sulfate is about 100
times more soluble, so most of it should stay in
solution. I have not tried this, but it “should work”
on paper, and the materials should be easy enough to
get and very safe.
Did you need to demonstrate anything else in
particular, or simply a double replacement
(metathesis) reaction? Beware of trying anything
quantitative with this type of reaction. The product
does dissolve to some degree, and precipitates are
notorious for getting through filtration devices, even
after “digestion” in certain cases.
Hope this helps
Roy Mayeda
Wheaton High School
Wheaton, MN
Where “salting” the sidewalk IS necessary to keep it
from becoming a thrill ride.
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