Text 6618, 94 rader
Skriven 2006-10-16 18:45:00 av JOAN MACDIARMID (1:123/140)
     Kommentar till en text av MARK LEWIS
Ärende: Vinegar
===============
 Hi, Mark,

 ML> i also had to google "reagent grade" as well as "glacial acetic
 ML> acid"... whoa! that's some interesting stuff!

 ML> 98% pure water free acetic acid

 Jim W. caught us in this! 98% is tech grade, not reagent grade.

 ML> explosive when mixed with air (or was that oxygen?)
 ML> at "low heat" temps (38.9C, 102F)

 JM>  Nah. I think that only means it's easily flammable
 JM>  in air if ignited. It doesn't go off spontaneously.
 JM>  Freezing isn't a problem, after all. You warm it
 JM>  up, it melts into the same liquid it was before
 JM>  it crystallized.

 ML> =======================================================================
 ML> === Concentrated acetic acid is corrosive and must therefore be handled
 ML> with appropriate care, since it can cause skin burns, permanent eye
 ML> damage, and irritation to the mucous membranes. These burns or blisters
 ML> may not appear until several hours after exposure. Latex gloves offer
 ML> no protection, so specially resistant gloves, such as those made of
 ML> nitrile rubber, should be worn when handling the compound. Concentrated

 I am surprised to hear latex offers no protection.
 At least it would slow stuff down on its way to your
 skin so you could rinse the glove. But if one were
 planning to get right down into the stuff, like
 handling objects submersed in the acid for some
 reason, special gloves probably would be a good
 idea.

 ML> acetic acid can be ignited with some difficulty in the laboratory. It
 ML> becomes a flammable risk if the ambient temperature exceeds 39 øC (102
 ML> øF), and can form explosive mixtures with air above this temperature
 ML> (explosive limits: 5.4%-16%).

 OK, that's the flash point. It can in most cases
 be handled safely at this point, but one would need
 to avoid ignition sources. Not a problem in most
 chemical labs, but a likely problem in uncooled
 storage warehouses or shipping trucks in the summer!

 ML> Solutions at more than 25% acetic acid are handled in a fume hood
 ML> because of the pungent, corrosive vapour. Dilute acetic acid, in the
 ML> form of vinegar, is harmless. However, ingestion of stronger solutions
 ML> is dangerous to human and animal life. It can cause severe damage to
 ML> the digestive system, and a potentially lethal change in the acidity of
 ML> the blood.

 As with most things, concentration is the key!

 ML> diluting that to usable levels would require a protective gearing up,
 ML> gloves, respirator, mask, and a measuring utensil that wouldn't get

 JM>  Again, nah! Even at 98% purity, acetic acid is
 JM>  intrinsically a "weak acid" (that's a specific
 JM>  chemistry concept I don't want to explain) but
 JM>  it is in no way comparable to sulfuric or
 JM>  hydrochloric acids.

 The vapors would probably make you sneeze, of course.

 ML> right... i understand that... it is also known as an ethanoic acid...
 ML> it is a weak acid based on its ability to dissociate in aqueous
 ML> solutions... it is also one of the simplest carboxylic acids... the
 ML> only simplier one being formic acid...

 ML> how do you pronounce "carboxylic"??  car box ee lick??

 Americans would probably do so, or car box ILL ick (to put the stress
 in the right place. Brits might use a long I (eye) in the third
 syllable...they pronounce ethyl as EE-thile, anyway.

 JM>  If I spilled glacial acetic
 JM>  acid on my hands, I would probably find it
 JM>  irritating and walk (not race) to the nearest
 JM>  sink to rinse it off. Sulfuric or nitric acids
 JM>  would blacken the skin almost immediately and
 JM>  leave a fearful burn if not washed off

 Of course, when I am handling any concentrated
 acid I am wearing some sort of gloves. Even flimsy
 vinyl ones give you a few seconds to react to a spill,
 back away and strip the gloves off, removing the
 acid with them. I am not stupid.

 [Splitting message: I try to keep them less than 100 lines]

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