From: Uncle Al <UncleAl0@ix.netcom.com>
Newsgroups: sci.chem
Subject: Re: Do somebody know what Sulfochromic acid is?
Date: Thu, 11 Sep 1997 19:04:17 -0700

Nicolas Poirier wrote:

> I'm curious to know what is the green liquid stuff in wich
> we clean the lab glassware.

It isn't green, it's red.  At the bottom line it is a solution of
chromium trioxide in concentrated sulfuric acid, carcinogenic Cr(VI).
It is a powerful acid and oxidizing agent - Jones reagent with an
attitude.  When it exhausts you get green Cr(III) or a grey ppt of the
anhydrous sulfate.

My tastes go toward KOH/ethanol.  Getting the last traces of chromium
off glassware is a real pain.

--
Uncle Al Schwartz
UncleAl0@ix.netcom.com ("zero" before @)
http://www.ultra.net.au/~wisby/uncleal.htm
 (Toxic URL! Unsafe for children, Democrats, and most mammals)
"Quis custodiet ipsos custodes?"  The Net!

Newsgroups: sci.chem
From: B.Hamilton@irl.cri.nz (Bruce Hamilton)
Subject: Re: Chromic Acid Cleaning Solution
Date: Fri, 20 Dec 1996 13:14:09 LOCAL

In article <32B7280F.4B11@bobo.acs.uiuc.edu> 
Subramani Iyer <siyer@bobo.acs.uiuc.edu> writes:

>Where would I find the recipe for making chromic acid
>solution for cleaning glassware?  

There are several alternative cleaners available that
do not have the corrosiveness, toxicity and
environmental pollution of chromic acid, and your
institution may no longer permit the use of chromic
acid for cleaning glassware.

The following procedure is how I was taught, and the
resulting chromic acid is stable for years without
precipitation, and seems to be a far more effective
cleaner than just dissolving the salts in the acid,
however the latter method is also used by some
people.

* However * the procedure is hazardous, as it 
involves adding an aqueous solution to concentrated
sulfuric acid, with the consequent possible generation 
of splatters and aerosols, and the definite generation
of heat. Obviously, fume cupboard, gloves and facemask 
should be used.

If you are not sufficiently familar with laboratory procedures 
for handling litre quantities of thick, viscous, concentrated 
acids, examination of glassware for cracks, and how to 
safely stir with glass rods in glass beakers, please don't
try the procedure without expert help. 

Sodium dichromate dihydrate is usually used as potassium
dichromate is less soluble in acid. I usually dissolve 140g in 
approximately 100 ml of water. I add two litres of technical
grade 98% sulfuric acid to a 4-5 litre glass beaker that is sitting 
in a cold water bath in a fume cupboard. I carefully stir the acid 
gently and pour a few mls of the dichromate solution slowly into 
the acid. I keep repeating the addition every few seconds after
the previous dose as been dispersed. As long as the stirring is 
gentle and continuous, little or no splattering should occur and
the solution will become quite warm. Allow to cool. 

If made correctly, the solution should have no precipitate, and 
be a deep red colour, and will last for years in a glass-stoppered 
bottle. Ensure the glassware does not have any residual organic
solvents. It is very effective at around 80C, but overnight at 
ambient temperature is commonly used. If the solution develops
a green hue, it is exhausted and should be disposed of using
appropriate procedures. Slowly pouring down a drain with the
cold water tap fully open is no longer considered appropriate. 

                    Bruce Hamilton

Subject: Re: Chromic Acid Cleaning Solution
From: Alan \"Uncle Al\" Schwartz <uncleal0@ix.netcom.com>
Date: Dec 18 1996
Newsgroups: sci.chem

Subramani Iyer <siyer@bobo.acs.uiuc.edu> wrote:

>Where would I find the recipe for making chromic acid
>solution for cleaning glassware?  

Cr(VI) is a nasty carcinogen (consider eventual disposal) and chromic 
acid cleaning solution is really hazardous stuff.

Try the "Chemist's Companion."  We used a big battery jar.  A couple of 
gallons of conc. H2SO4 and maybe a half pound of potassium dichromate 
added slowly with stirring (goggles, heavy high ribber globes, rubber 
apron- it exotherms).  Cover with a pyrex plate.  Add more dichromate as 
necessary to maintain a deep red color.  NEVER USE A PLASTIC TUB!  The 
stuff eats right through.

Except for metal oxides and Apiezon grease, I much prefer a gallon of 
EtOH and a pound of KOH in a polyethylene bucket with a tight cover.  

-- 
Alan "Uncle Al" Schwartz
UncleAl0@ix.netcom.com ("zero" before @)
http://www.ultra.net.au/~wisby/uncleal.htm
 (Toxic URL! Unsafe for children, Democrats, and most mammals)
"Quis custodiet ipsos custodes?"  The Net!