Bad smells from over charging lead acid batteries

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Over the weekend someone had left a charger on a lead acid battery,
seriously overcharging the battery. It stunk up the whole shop with a
sulfur smell. I know when you overcharge you get hydrogen and oxygen
gas, and from the smell there is obviously some sulfur. That exhausts
my knowledge of battery chemistry, does anyone know what the actual
chemistry is?

Nearby we had some copper tubing that was discolored. Some of the
shop guys blamed that on the gas from the battery. Is that plausable?

Ethan

 

[Glen Walpert]

Actually the "sulfur smell" is hydrogen sulfide. Sulfur by itself
doesn't smell that bad. There was no shortage of hydrogen produced in
overcharging the battery, but hydrogen by itself doesn't really have a
smell. The free hydrogen combines with other random atoms it finds,
and even though sulfur isn't the most common element, when hydrogen
combines with sulfur in a confied space the result stinks to high
heaven.


The green tinted copper corrosion is copper sulfate. I think the
relation to your previous question, is that this shows that there is
no real shortage of sulfur compounds in your room. Blaming the
hydrogen for the presence of sulfur compounds is a little like blaming
the sun for letting you see ugly women .

Seriously overcharged lead acid batteries emit more than just
hydrogen. The bursting bubbles cause electrolyte misting and
evaporation, with enough flow rate to carry significant acid out of
the battery, and in severe cases the electrolyte can boil. There are
also a number of other reactions going on including one which releases
small amounts of Stibene from the Antimony (Sb) used to strengthen the
lead alloy plates.

(Normal charging releases pretty much the same stuff in smaller
quantities; hence TFM recommends ventilation.)

www.apcmedia.com/salestools/SADE-5TNQZQ_R1_EN.pdf
http://www.springerlink.com/content/m1660445062t2054/

---------
Stibine
From Wikipedia, the free encyclopedia

Stibine is the chemical compound with the formula SbH3. This
colourless gas is the principal covalent hydride of antimony and a
heavy analogue of ammonia. The molecule is pyramidal with H–Sb–H
angles of 91.7° and Sb–H distances of 1.707 Å (170.7 pm). This gas has
an offensive smell like hydrogen sulfide (rotten eggs).

Safety

SbH3 is an unstable flammable gas. It is highly toxic, with an LC50 of
100 ppm in mice. Fortunately, SbH3 is so unstable that it is rarely
encountered outside of laboratories.

Toxicology

The toxicity of stibine is distinct from that of other antimony
compounds, but similar to that of arsine.[6] Stibine binds to the
haemoglobin of red blood cells, causing them to be destroyed by the
body. Most cases of stibine poisoning have been accompanied by arsine
poisoning, although animal studies indicate that their toxicities are
equivalent. The first signs of exposure, which can take several hours
to become apparent, are headaches, vertigo and nausea, followed by the
symptoms of hemolytic anemia (high levels of unconjugated bilirubin),
hemoglobinuria and nephropathy.

 

[richard]

The "acid" in a lead-acid battery is sulfuric acid (H2SO4). When you
overcharge a battery it generally gets hot enought to boil the acid, which
in turn vaporizes a fraction of the acid. THe acid vapor escapes through
the vented caps of the battery and is quite happy to recondense to liquid
acid on anything cool in the area ... like copper tubing at room
temperature. THe discoloration is a sulfur compound of copper, either the
sulfate or the sulfide. One is green and one is black but I disrember which
is which.

The sulphate is blue and the sulphide is black.
But does H2SO4 react with copper ?

 

[Jasen Betts]

The sulphate is blue and the sulphide is black.
But does H2SO4 react with copper ?

CuSO4 is stable, so yes, I don't think it's a vigourous reaction at
room temperature though,

 

[richard]

Yes. Quite vigorously given the chance (like drop a bit in 1 molar
H2SO4), with much release of H2 gas. Vapors will corrode copper pipe
in a hurry.
.

Sorry, I don't believe that. Copper is below Hydrogen in the electrochemical series (along with similar "inert" metals - Gold,
Silver, Hg)

Cu does not react with H2SO4 appreciably at room temperature.

In order to increase the reaction rate between Zn & H2SO4, one adds a crystal or drop of CuSO4 solution. The Zn reacts with the
CuSO4 precipitating Cu which creates a "Zinc-Copper couple" which (I guess) makes it easier for the Zn to go into solution (like
rusting).

Do the experiment (and remember to add the concentrated acid to the water - and not the other way round).

 

[richard]

The issue is not the H2, the issue is the (hot) H2SO4 {(aq)?} vapor.
See:

http://jchemed.chem.wisc.edu/JCEsoft/CCA/CCA3/MAIN/CUNASID/PAGE1.HTM

Thanks for the reference.
I had not tried with hot conc H2SO4 - only cold dilute (eg 1 molar) - to confirm my memory before going public.

And OK not vigorously without a little bit of zinc to catalyze and
participate. See also brass fittings.

Was the stuff on the copper pipe blue or green? Likely to be copper
sulfate or similar. IIRC No mention yet of anything else in the
vicinity that could produce copper salts.
Perhaps with an H2O2 intermediary producing copper oxide (which is
conveniently green). The 4th oxygen from the sulfate ion may produce
H2O2.

2 H2SO4(aq) + 2 Cu(s) yeilds SO2(g) + H2(g) + CuSO4 + CuO + H2O ??

This does not produce any H2O2 and the CuO should preciptiate.

remnants of flux (perhaps containing Ammonium Chloride) can cause green corrosion

Alas, i do not currently have shelf access to such simple chemicals
these days.

Yes, more difficult to obtain as pure chemicals these days, but some drain cleaners contain "commercial" H2SO4

If I had to make H2SO4 I'd do it with sulphur, to make SO2 and pass that with air over Vanadium Pentoxide to make SO3


I think that Glen Walpert gave the most plausible answer - certainly the most interesting.