Re: buffer, bicarbonate, dancing angels
> From: Elizabeth Worobel <eworobe at cc_UManitoba.CA>
> Date: Sat, 11 Jan 1997 09:57:35 -0600 (CST)
> Subject: Re: Alkalinity
> > Hi everyone,
> > The other day I picked up Tetra's book "Aquariology, Master Volume". In it,
> > it states:
> > "Sodium Bicarbonate is a pH adjuster rather than a buffer. If added in
> > excess to an aquarium, the pH can be elevated to unacceptably high levels.
> > A 10% solution of baking soda can safely be used to raise the pH of an
> > aquarium.
> > ...
> > Also, since Sodium Bicarbonate by itself is not a buffer, the desired pH
> > may not hold for very long."
> > So, who's right? Or am I confusing KH (Carbonate Hardness) and Alkalinity
> > (Acid Binding Capacity)? Am I totally confused yet????
> George, of course, is correct. As usual the so called aquarium 'experts'
> havent got a clue.
Not that I want to defend Tetra writers, but...
I understand the sense in which the word buffer was being used above. A
solution of pure sodium bicarbonate in water is a lousy buffer at the
initial pH. Indeed, the buffering capacity is at an absolute minimum at
that pH. As one adds acid or base, it gets progressively harder to
change the pH as more acid/alkali are added.
I believe that the author was trying to disabuse the idea that one can
take a 1 molar solution of sodium bicarbonate and add 1 part of it to the
aquarium or 100 parts and get the same final pH. That is because this is
a volatile buffer system that is in equilibrium with the atmosphere.
USUALLY when people say "buffer" they are talking about a mixture of an
acid and conjugate base. Alone, bicarbonate ions don't fulfill that
definition, although when they are paired with H2CO3/CO2 or carbonate
ions, they do.
My personal view is that sodium bicarbonate is most usefully called a
carbonate alkalinity booster. I'd be reluctant to call it a buffer by
itself, but it is completely fair to say that adding sodium bicarbonate can
increase the buffering capacity of the aquarium. Indeed, it increases
both the total alkalinity and total acidity of the aquarium. ;)
You could also call it a kH booster, but I might barf on you if you used
that word around me.
next week: the long awaited answer to how many angels can dance on a frog