From: "Paul H. Merrill" <paulmerrill@acm.org>
Date: Wed, 28 Jan 1998 23:40:45 +0800
To: Rabid Wombat <wombat@mcfeely.bsfs.org>
Subject: Re: State of the Union Address
In-Reply-To: <Pine.BSF.3.91.980127113443.14544C-100000@mcfeely.bsfs.org>
Message-ID: <34CF78E9.5F29@acm.org>
MIME-Version: 1.0
Content-Type: text/plain



Rabid Wombat wrote:
> 
> On Tue, 27 Jan 1998, Paul H. Merrill wrote:
> 
> > Rabid Wombat wrote:
> > >
> > > On Sat, 24 Jan 1998, Matthew Ghio wrote:
> > >
> > > > Anonymous wrote:
> > > >
> > > > > [1] Grab a totally random sample of 100 high school students. Haul the
> > > > >     students out one at a time and ask them the following questions:
> > > > [snip]
> > > > > 11) Michelle mixes one gram of HCl and one half gram of NaOH. Under normal
> > > > >     circumstances, what is produced and in what quantities?
> > > > >
> > > >
> > > > The correct answer is an explosion and a big mess.  One student in my high
> > > > school chemistry class learned this the hard way.  :)
> > > >
> > > >
> > >
> > > Um, salt water explodes?
> >
> > I guess those high school students aren't the only ones with no clear
> > idea of the way the world works.  While salt water does not ordinarily
> > explode, in this case salt water is the ultimate product -- but massive
> > heat released when acids and bases join and recombine to produce salts
> > (in this case table salt) and water.
> >
> > while some do feel (especially on this list) that the ends justify the
> > means -- this is one means that definitely does not go along with that
> > "rule".
> >
> > PHM.
> >
> 
> Actually the qustion is probably hosed, as the ratio should be 1:1
> Hcl:NaOH mol, not weight (which would be about 10:9 Hcl:NaOH or so if I'm
> not confused here) ...  the idea being that if you calculate and measure
> just right, you can mix too highly dangerous chemicals and will get
> saltwater which you can drink. If you don't measure just right, and drink
> it, you are rightly fucked, so don't try this at home.
> 
> Can't find exact delta-h listed for NaOH, but rough guess on this reaction
> is maybe 150,000 - 175,000 joules, or about half a box of kitchen matches
> worth of heat (~150-175 btu ?), which wouldn't boil a quart of water. I
> suppose if you had a small enough solution you could get a small "bang"
> out of vaporizing the water. Not exactly a terrorist threat.
> 
> A moderate amount of heat, but without increasing the number of
> molecules, where's the explosion? Am I missing something? Looks like warm
> saltwater to me. OTOH, I don't know anything about chemistry 'cuz I
> always got kicked outa class for doing dumber things than mixing Hcl and
> NaOH and drinking it, which is the usual stunt. Don't try this at home,
> and don't take chemistry advice from marsupials.
> 
> btw - didn't really "do the math" on this, and it's 2am, so it could be
> wildly innacurate.
> 
> -r.w.

yes, the quantities are small, thus total heat is small, but so is the
mass to be heated (who cares idf it will boils a quart when we are
talking about a couple of grams).  Explosion is perhaps a poor choice of
words, but I would not like to be in the spatter zone of it either.

PHM