Ask A Scientist© Chemistry Archive

name        Erika Brown
status      student
age         20s

Question -  I am a photography student and I am working on a project
where I am making film developer out of coffee. The recipe for the developer
asks for Potassium Hydroxide. It requires me to mix this with baking
soda, coffee, and water. I am quite concerned about mixing it with
water after researching it because of all of the warnings say not to
mix the two together. My question to you is how safe is it to mix
Potassium Hydroxide with water?
I really have no idea what exactly can happen.
Thank you very much.
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Solid potassium hydroxide, like solid sodium hydroxide, releases a large
amount of heat when dissolved in water. To prevent overheating, add the
potassium hydroxide TO THE WATER SLOWLY, not the other way around. The heat
capacity of the water will help absorb the heat.
If you want added precaution place the vessel in an ice bath.

Your concern for safety is commendable. Also wear eye shields and protective
gloves. Even disposable latex or polyethylene gloves are adequate.

Vince Calder
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The hazard associated with mixing KOH (potassium hydroxide) with water is
that it generates a lot of heat as it dissolves. This can lead to
spattering. A concentrated KOH solution will erode skin and eyes. These
hazards can be avoided by wearing safety glasses and rubber gloves, and
immediately rinsing with water if any skin contact occurs. (If any eye
contact occurs, flush the eyes with water for 15 minutes and then get
medical attention.)

The proper way to combine KOH and H2O is to add the KOH slowly to cool water
with gentle stirring.

Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois
=========================================================
I recommend that you obtain and read a MSDS (Material Safety Data Sheet) for
the potassium hydroxide(KOH).  It will have instructions and guidance for
safe handling that I could not adequately cover here.  KOH, like most bases,
is extremely corrosive to most living tissue, so direct contact with KOH and
its solutions should be carefully avoided.  (Wear at least proper gloves and
goggles, and have someone within easy earshot to help get you to the
eyewash/safety shower, just in case!) To prepare the solution you need,
start with the required amount of COLD water in a container 2 to 4 times the
size required to hold the final solution.  Add the KOH slowly, mixing gently
to dissolve the material before adding more.  Putting the mixing vessel in a
tub of icewater to control the heat created while the KOH dissolves will
further enhance safety and processing.
Tim Spry
=========================================================
The reaction of a strong base (such as potassium hydroxide) and water will
generate quite a bit of heat.  If performed slowly and with care this should
not be a problem.  Always add the other chemicals, such as the potassium
hydroxide, to the water rather than the other way around.

With typical quantities (250 ml of water) you might want to take 5 to 10
minutes to mix them.  If the reaction beaker gets hot, stop adding chemicals
and stir until it cools down.  Adding the KOH to the water will ensure that
the mixture is always relatively dilute and also keep it cooler.

'Care' means stirring the chemicals to mix them well as you combine them.  It
also means wearing the appropriate protective clothing such as goggles or a
face shield and a lab coat, or old clothes that you wouldn't mind having
holes in if you have a spill or splash.
Bradburn
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