Glass Cleaners

Standard Glassware Cleaning Solutions, stolen from the Chemist’s Companion
Routine, simple cleaning is conveniently accomplished by brushing with detergent or soap
solution; special products are available (such as “Alconox”) that act as wetting agents. (The
Microsoap we stock in the OEML is claimed to leave less residue.) Laboratory glassware
washing machines are also sold, as well as ultrasonic cleaning baths. (Ultrasonic baths are really
good at cleaning dirt from cracks and crevices and other places you have a hard time getting into.
They are also an aid to dissolution. Never run an ultrasonic cleaner without an inch of water or
some other liquid in them.) However, hard-to-clean glassware is most often treated with
solutions described below. It is economically advisable to buy technical grade chemicals for
their preparation.
A. Chromic Acid (Not recommended, see below. It is very effective but has undesirable side
For routine cleaning (burettes, pipes, etc.), add slowly with stirring 800 cc concentrated H2SO4 to
a solution of 92 g Na2Cr2O7  2H2O in 458 cc H2O. Alternatively, add 1 liter of acid to 35 cc
of a saturated aqueous sodium dichromate solution; the latter solution is obviously more
concentrated and is used for very difficult cases. When the red-brown solution turns green or
becomes too diluted after use, discard. Potassium dichromate may also be used, but is
considerably less soluble than the sodium compound. Very many (>10) washings of the
glassware with demineralized water are necessary to remove traces of chromium ions if desired.
For use in chelometric titrations and the like, treat the acid-washed glassware as follows for a
more effective metal “decontamination”: soak for a couple of hours with a solution (aqueous)
containing 1% disodium ethylenediaminetetraacetate and 2% NaOH; rinse several times with
demineralized water. This approach has fallen into disfavor over the years due to the toxicity of
hexavalent chromium. Any solution containing more than 5 ppm of chromium must be disposed
of as hazardous waste, and this exceeds the limit by many orders of magnitude. Needless to say,
it is extremely corrosive to tissue, another considerable drawback!
A ready-made dichromate concentrate is sold, which is added to a standard 9-lb bottle of H2SO4
to make cleaning mixture (“Chromerge”; Manostat Corp., 20 North Moore Street, New York,
N.Y.). Other products are available, such as ready-to-use “Dichrol” (Scientific Products, 1210
Leon Place, Evanston, IL 60201).
B. Alcoholic Sodium (Potassium) Hydroxide
Add about 1 liter of 95% ethanol to 120 cc water containing 120 g NaOH (or KOH). A very
powerful cleaning medium, but prolonged exposure will damage (by etching) ground glass
C. “Nochromix”
This inorganic oxidizer contains no metallic ions. The white powder is dissolved in water and
mixed with concentrated H2SO4, giving a solution that is reportedly more strongly oxidizing than
chromic acid. The solution is clear, but turns orange as the oxidizer is used up. Available from
Godax Laboratories, 6 Varick Street, New York, N.Y. 10013. Also available from the Chemistry
Stockroom, stock number C356.
D. Sulfuric-Fuming Nitric Acids
A mixture of the two is especially good for very greasy, dirty glassware. Needless to say, this
will also be extremely corrosive to tissue. Alternatively, grease may be removed by soaking in
warm soap solution for  1 hr; after rinsing with H2O soak in concentrated HC1.
E. Trisodium Phosphate
To remove carbon residues, soak for several minutes in the following solution and brush off the
incrustation: trisodium phosphate (Na3PO4) - - 57g; sodium oleate - - 28.5 g, water - - 470 cc.
Carbonaceous material may also be moved with 10 to 15% aqueous NaOH or KOH.
F. Pirana etch: composition and uses
A piranha is used to remove organic residues from substrates. Two different solutions are used. The most
common is the acid piranha: a 3:1 mixture of concentrated sulfuric acid (H 2SO4) with hydrogen peroxide
(H2O2). Also used is the base piranha: a 3:1 mixture of ammonium hydroxide (NH4OH) with hydrogen
peroxide (H2O2). Both are equally dangerous when hot, although the reaction in the acid piranha is selfstarting whereas the base piranha must be heated to 60 degrees before the reaction takes off. [1]
There are many things which will cause the reaction to accelerate out of control. "Out of control" can
mean anything from the piranha foaming out of its bin and on the deck, to an explosion with a huge shock
wave including glove and acid-gown shredding glass sharps. Piranhas burn organic compounds. If you
provide sufficient fuel for them (i.e. photoresist, IPA), they will generate enormous quantities of heat and
From Leonard Wojcik, chemist extraordinaire:
I only rarely use chromate (conc H2SO4, potassium dichromate). 1) it leaves a chromium residue
on the glass. 2) You have to use it hot. 3) While it is meaner than Piranha, it is also a disposal
problem (not supposed to be washed down the drain). 4) Piranha will remove graphite from
glassware if you have patience (a few days). It also works more vigorously if heated. Disposal
is not a problem, because once it is spent, you are only disposing of H2SO4.
Best mix: Conc H2SO4 (4 liters), 50% H2O2 (50 ml). It is most active when the acid is
concentrated, therefore use the most concentrated H2O2 available, and minimal added water therefore 50% H2O2