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?
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.)
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--------- 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.
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.
Jim
--
"It is the mark of an educated mind to be able to entertain a thought
without accepting it."
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).
The issue is not the H2, the issue is the (hot) H2SO4 {(aq)?} vapor. See:
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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.
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