Date: Thu, 8 Jun 1995 10:57:08 -0700 (PDT)
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: tfab@netcom.com (thom fitzpatrick)
Subject: Distilled vs. Tap H20, chemical explanation. (fwd)
I got this off the Porsche list, and I thought it was a pretty good
disertation on rust and "proper" antifreeze, both of which are irrelevant to
me because I live in California and have only air-cooled cars!
BLenoble@aol.com coughed up:
> From porschephiles-request@tta.com Thu Jun 8 10:37:24 1995
> From: BLenoble@aol.com
> Date: Thu, 8 Jun 1995 13:16:45 -0400
> Message-Id: <950608131644_89843887@aol.com>
> To: porschephiles@tta.com
> Subject: Distilled vs. Tap H20, chemical explanation.
>
>
> >From my brother the Chemist:
>
>
> >I decided to do a little experiment. I polished a small sheet of
> >aluminum, washed it with a solvent, and cut off 4 strips. I placed
> >each strip in identical jars which had been cleaned in a laboratory.
> >I filled each jar as follows:
> >
> >1. 100% distilled water
> >2. 100% tap water
> >3. 100% Prestone
> >4. 50% Prestone, 50% distilled water
> >
> >That was May 19th. Today, here are the results so far:
> >
> >1. White precipitate (flakes) coating the top surface of the
> >aluminum. (looks almost like 1 mm specs of dandruff) There are
> >also flakes settled at the bottom of the jar.
> >
> >2. About 1/4 the precipitate of jar 1. The flakes are much smaller,
> >almost making the water look cloudy rather looking like they are in
> >suspension.
> > Also visible are small gray specs of corrosion on the aluminum
> >(not visible in jar 1 perhaps due to the thick coating of flakes).
> >
> >3 & 4. No discernable precipitate or cloudiness. Aluminum surface
> >still as satiny as when first polished.
> >
> >So jars 3 & 4 proves what we all know already, that antifreeze
> >prevents corrosion. Only time will tell whether my use of an
> >antifreeze which probably has phosphates will make any difference.
> >Unfortunately, I don't have phosphate-free antifreeze to use for a 5th jar.
> >
> >However, jars 1 and 2 behave the opposite as I would have expected.
> >Any chemists out there to explain why using distilled water produced more
> >precipitate than tap water?
> >
> >Joe '86 944
> >
>
>
> This is actually an interesting question from a chemistry
> point of view. Being an analytical chemist and not a
> inorganic chemist this is not my direct forte. I will give
> my attempt at an explanation.
>
> Here goes; First we need to think about what corrosion is to
> understand the chemistry involved. Corrosion, as used in
> this E-Mail, would be the oxidation of metals to form metal
> salts and precipitates. Different metals will oxidize to
> form different metal salts. Rust is the classic oxidation
> product of Iron.
>
> For those who forgot their general chemistry oxidation is
> the loss of electrons. This is promoted by what is called a
> oxidizing agent. An oxidizing agent is something that wants
> an electron or is electron deficient. Chlorine (Cl) is one
> of the best oxidizing agents there is. Cl is one electron
> short of a full electron state. So it will take an electron
> from anywhere it can.
>
> Next we must look at what metals come in contact with the
> coolant to figure out what things may be corroded. In most
> cars that would be Iron (Fe), Aluminum (Al), and steel
> (which is a blend of Fe, Carbon, and other metals, like
> Nickel (Ni) and Chromium (Cr). Any of these can be oxidized.
>
> Al is easily oxidized, more so then Fe or steel. The reason
> that Al looks dull is the surface is oxidized and this
> prevents further oxidation. If you polish Al it will oxidize
> immediately and if you continue to polish it will continue
> to oxidize.
>
> Now to the heart of the matter. Why did they Al in distilled
> water oxidize more then in tap? The answer is that distilled
> water is more reactive then tap water. This is because in
> distilled water you need to think of the water as a lose
> association of H+ and 2O- ions. These ions can react or
> oxidize metals. Tap water has other ions like (Fe3+, Mg3+,
> Fe2+, Ca2+, Cl-, F-). These ions will form lose
> associations with the H+ and the O- and make the water less
> reactive.
>
> The bottom line is that you should use antifreeze and tap
> water as your coolant. Antifreeze is designed to help
> prevent corrosion. At some other time I can talk about what
> is in antifreeze and how it works.
>
> Send your next chem question at Rod.Lenoble@Hauser.com
>
> Barry Lenoble
> Blenoble@aol.com
> 89 944 Turbo, Alpine White
>
>
--
Thom Fitzpatrick
tfab@netcom.com
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