Text 6476, 231 rader
Skriven 2006-10-13 12:21:08 av mark lewis (1:3634/12.0)
Kommentar till text 6335 av JOAN MACDIARMID (1:123/140)
Ärende: Vinegar
===============
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
ML> freezes at room temp (16.7C, 62F)
ML> explosive when mixed with air (or was that oxygen?)
ML> at "low heat" temps (38.9C, 102F)
ML> this stuff is only stable within a 40F degree range!
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.
i've had to wait until i had a chance to get back over and locate that info...
so here it is from wikipedia...
===== quote http://en.wikipedia.org/wiki/Glacial_acetic_acid =====
Safety
==========================================================================
Concentrated acetic acid is corrosive and must therefore be handled with
appropriate care, since it can cause skin burns, permanent eye damage, and
irritation to the mucous membranes. These burns or blisters may not appear
until several hours after exposure. Latex gloves offer no protection, so
specially resistant gloves, such as those made of nitrile rubber, should be
worn when handling the compound. Concentrated acetic acid can be ignited with
some difficulty in the laboratory. It becomes a flammable risk if the ambient
temperature exceeds 39 øC (102 øF), and can form explosive mixtures with air
above this temperature (explosive limits: 5.4%-16%).
The hazards of solutions of acetic acid depend on the concentration. The
following table lists the EU classification of acetic acid solutions:
=================================================================
| Concentration | | | |
| by weight | Molarity | Classification | R-Phrases |
|===============================================================|
| 10%-25% | 1.67-4.16 mol/L | Irritant (Xi) | R36/38 |
| 25%-90% | 4.16-14.99 mol/L | Corrosive (C) | R34 |
| >90% | >14.99 mol/L | Corrosive (C) | R10, R35 |
=================================================================
Solutions at more than 25% acetic acid are handled in a fume hood because of
the pungent, corrosive vapour. Dilute acetic acid, in the form of vinegar, is
harmless. However, ingestion of stronger solutions is dangerous to human and
animal life. It can cause severe damage to the digestive system, and a
potentially lethal change in the acidity of the blood.
===== end quote =====
ML> i also hunted up "grain" as a measure of strength in vinegar... i
ML> wasn't able to find out how they came up with it but did find that it
ML> is simply 10 times the acidity percentage... 3% == 30grain, 4.5% ==
ML> 45grain, 9% == 90grain... that would mean that glacial acetic acid,
ML> with its 98% purity, would be some 980grain if i'm understanding things
ML> correctly...
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.
right... i understand that... it is also known as an ethanoic acid... it is a
weak acid based on its ability to dissociate in aqueous solutions... it is also
one of the simplest carboxylic acids... the only simplier one being formic
acid...
how do you pronounce "carboxylic"?? car box ee lick??
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
JM> immediately.
no doubt...
JM> Hydrochloric liquid acid is less
JM> harmful, because it is only about 36% in water,
JM> but the 100% is pretty nasty as a gas (I inhaled
JM> a plume of it once in a small accident, and had
JM> horrific nosebleeds because of the tissue damage).
no doubt... i've used liquid hydrochloric acid at eat drain stoppages... you
gotta be very careful and make sure that you have some kind of container
inverted over the drain to trap the gases... then, use plenty of water to flush
the pipes and dilute the acid! :)
JM> Acetic is relatively bland stuff. Any plastic
JM> utensil would handle it, and most metal ones
JM> in common use.
i know it is used in a great many foodstuffs... that's for sure ;)
ML> eaten... then you're looking at something like 1/4 teaspoon
ML> of GAA to 5 gallons of water O8-)
way outta range and thus the halo smiley :)
ML> to figure out how much water it would take to break 98% water-free GAA
ML> down to 5%... we'd have to add 93% water (ignoring the other 2%
ML> variable)...
ML> 98 - 93 = 5
ML> simple enough...
JM> Too simple! Taking the 98% seriously (no, I don't
JM> know what the other 2% is, arguing against using
JM> reagent acetic acid!), 1 unit x 0.05=V units x 0.98,
JM> This reduces to V units = 0.05/0.98 x 1 unit, or
JM> 0.51 units per unit of finished volume of 5%
JM> acetic acid! So you would want 5.1 parts of Glacial
JM> to 94.9 parts water to get it exact. Still, it's
JM> close to your idea of taking 5 parts one, 95 parts
JM> of another, and good enough for cooking.
hey! thanks! i was trying to remember all that formulation maths stuffs... it
has been far too long... but i had the right idea and just went with the simple
method to get there... i did sneak in back and use a "units conversion
calculator" though... i had originally started trying it with teaspoons as i
had just grabbed that outta the air above... once i saw some numbers, i just
switched to "units" and since 98% is so close to 100% it made for very easy
math ;)
JM> Seriously, I think cooks should stick to natural
JM> vinegar! The glacial is mostly made from petroleum
JM> sources by chemical procedures, and who knows what
JM> stray byproduct molecules are in that 2%? Natural
JM> vinegar at least originated from plant sources
JM> which mostly contributed carbohydrates to a
JM> fermentation to give stuff we know is mostly
JM> carbon/hydrogen/oxygen. It usually tastes better,
JM> too! Cider vinegar is rather nice on its own,
JM> diluted enough and sweetened!
i hear ya there!
===== quote =====
The global demand of acetic acid is around 6.5 million tonnes per year (Mt/a),
of which approximately 1.5 Mt/a is met by recycling; the remainder is
manufactured from petrochemical feedstocks or from biological sources.
===== end =====
===== quote =====
General
Systematic name Acetic acid
Ethanoic acid
Other names Methanecarboxylic acid
Acetyl hydroxide (AcOH)
Hydrogen acetate (HAc)
Molecular formula C2H4O2 or CH3COOH
SMILES CC(=O)O
Molar mass 60.05 g mol-1
Appearance Colourless liquid
or crystals
CAS number [64-19-7]
Properties
Density and phase 1.049 g cm-3, liquid
1.266 g cm-3, solid
Solubility in water Fully miscible
In ethanol, acetone Fully miscible
In toluene, hexane Fully miscible
In carbon disulfide Practically insoluble
Melting point 16.7øC (289.9 K) (62.1øF)
Boiling point 118.1øC (391.2 4K) (244.6øF)
Acidity (pKa) 4.76 at 25øC
Viscosity 1.22 mPaús at 25øC
Dipole moment 1.74 D (gas)
Hazards
MSDS External MSDS
EU classification Corrosive (C)
NFPA 704 health 2
flammability 2
reactivity 0
other hazards 'blank'
Flash point 43øC
R-phrases R10, R35
S-phrases S1/2, S23, S26, S45
U.S. Permissible
exposure limit (PEL) 10 ppm
Supplementary data page
Thermodynamic Phase behaviour
data Solid, liquid, gas
Spectral data UV, IR, NMR, MS
Related compounds
Related carboxylic Formic acid
acids Propionic acid
Butyric acid
Related compounds Acetamide
Ethyl acetate
Acetyl chloride
Acetic anhydride
Acetonitrile
Acetaldehyde
Ethanol
Except where noted otherwise, data are given for
materials in their standard state (at 25øC, 100 kPa)
Infobox disclaimer and references
===== end =====
lottsa interesting stuff there... and just think... it is all about vinegar
that we use in many recipes and food preparations...
)\/(ark
* Origin: (1:3634/12)
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