10 facts on...
by Philip McIntosh
Acid washed. Acid rain. Acid fast. Acid test. Okay, so what exactly is an acid?
IN THE SIMPLEST sense, an acid is a
substance that ionizes to generate hydronium
ions (H+ cations) when dissolved in water.
This is known as the Arrhenius definition. It’s
not scientifically very useful, but for practical
understanding, it is used often enough.
AN ACID can also be understood as a
substance that donates a proton (an H+ ion).
That is part of the Brønsted-Lowry definition.
THE ACIDITY of a solution
is described by its pH value.
pH is a measure of the H+ and
OH- concentrations in a solution.
H+
OH-
WHAT COULD be stronger
than an acid? A superacid.
Superacids have acidity greater than
100 per cent sulfuric acid and can be
trillions of times stronger. The pH
scale doesn’t properly work to
describe a superacid.
WHEN THE number of H+ ions
equals the number of OH- ions,
water is formed and there are few
free H+ ions. In this case, the
solution is neutral, which is 7 on
the pH scale. Solutions with pH
values less than 7 are acidic.
THE SOLUBILITIES
of many nutrient
elements are pH
sensitive, with acidic
conditions required
for good availability.
This is why grow
system pH values
should be monitored
and maintained in
the 5.5-6 range for
most applications.
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Maximum Yield USA | December 2016
ACIDS EXIST in a balance of
some kind with their chemically
opposite entities, the bases.
Bases generate OH- anions
readily when dissolved in water.
H2O
IT IS NO accident that when
H+ ions meet OH-ions, they
react to form H2O—water.
A WEAK ACID does not
release all of its protons when
dissolved. A strong acid ionizes
completely to release all of its
protons into solution.