In order to better understand some of the concepts of
inorganic chemistry in the marine aquarium, I want to outline
some basic chemical principals applied in this article. It is not
necessarily vital to understand or read this section, but it will
help in following some of the ideas and math. This section is
hardly meant to make chemists out of anyone. If anything, it is
more of a repetition to bring back that long lost loving feeling
for atoms, molecules, and the like.
Chemical compounds consist of molecules made up out of atoms.
When these compounds are dissolved in water they separate into
ions that are either positively or negatively charged. The charge
is dependent upon whether an atom gives up or receives one or
more electrons. This is done to reach a more stabile state. For
example sodium chloride (NaCl) dissociates into a positive sodium
ion (Na+) and a negative chloride ion (Cl-)
in water.
Each chemical element (or atom) has a characteristic weight.
The molecular weight of a compound is thus calculated by adding
the individual weights of the atoms in the molecule. This weight
-- in grams -- is based on one mole of the substance, which
contains a constant number of molecules. For example sodium (Na)
weighs 22.9898 grams per mole, and chlorine (Cl) weighs 35.453
grams per mole. Thus the combination of the two, sodium chloride
(NaCl), weighs 58.4428 grams per mole. These weights can be found
in a table of chemical elements called the Periodic
Table of the Elements.
Molecules react with each other in predictable ways. Energy
and mass cannot be lost and so it is possible to know how two or
more substances will react with each other. By setting up an
equation and balancing out both sides, it is known what
substances are available for a reaction. Making sure that both
sides are equal in number of the same atoms though is important.
For example, if one mole of calcium chloride (CaCl2)
is dissolved in water, it dissociates into one mole of Ca2+
and two moles of Cl-. Furthermore if one mole of
sodium bicarbonate (NaHCO3; baking soda) is added to
the solution, it will dissociate into one mole Na+ and
one mole of HCO3-.
By forming the equations for the
reactions one can determine what the results will be, when added
to water:
CaCl2 <==> Ca2+ + 2Cl-
NaHCO3
<==> Na+ + HCO3-
Calcium chloride has two chloride ions. Calcium has a double
positively charge that can only be balanced out by two chloride
ions with their single negative charges. Sodium and bicarbonate
ions each have opposite single charges. This means that sodium
bicarbonate consists of only one each of the ions.
If both reactions run in the same
medium, the following would result:
CaCl2 + 2NaHCO3
<==> Ca(HCO3)2 + 2NaCl
Two sodium bicarbonates are needed on the left because the
double positively charged calcium ion reacts with two single
negatively charged bicarbonates. Conversely since two single
negatively charged chloride ions are available from the calcium
chloride on the left, two single charged sodium ions are needed
to balance them out. A close look at the equation will show that
there is the same number of ions on both sides of the double
arrow.
Note: The double arrow signifies that the reaction can run
in both directions.
The concentration of dissolved chemicals is usually given in
one of two forms. The first being "percentage." This
form can either be a "weight to volume" or "volume
to volume" percentage. The second form is the
"molar" form. In this form the number of moles of the
substance is given per 1000ml (1 liter) of solution. An example
for the first form would be a 10% NaCl solution. Here 10g of NaCl
are dissolved in 100ml of water (weight / volume %). Another
would be a 3% vinegar solution, where 3ml of vinegar are
dissolved in 100ml of water (volume / volume %). An example of a
molar solution would be a one (1) molar NaCl solution. Here one
(1) mole of NaCl (approximately 58.4g) is dissolved in 1000ml (1
liter) of water. A two (2) molar solution would have two (2)
moles per liter, etc. Knowing the concentration enables one to
calculate exactly how much substance one is adding to the
aquarium in a given amount of solution.
When buying chemical compounds, especially the ones we will be
working with, knowing that some are hygroscopic is important,
meaning that they attract -- or bind -- water. This is normally
apparent by the fact they will clump up in damp environments.
This on the one hand makes it difficult to measure them
accurately and on the other hand changes the weight of the
molecules, making calculations based on the original molecule
invalid. One example would be calcium chloride (CaCl2),
a compound we will be using. When buying this substance, it is
imperative to know whether you are buying anhydrous, dihydrous or
hexahydrous compounds. Anhydrous CaCl2 has a weight of
110.986 g/mole, since Ca weighs 40.08 g/mole and Cl weighs 35.453
g/mole. The dihydrate form has two (2) waters added to this
weight. This means that one mole of this form weighs 147.0168
grams per mole, or 36.0308 grams per mole more (water weighs
18.0154 grams per mole). The result being that if one makes their
calculations based on the anhydrous form and adds dihydrate, less
calcium would be added to the system than intended. This would be
even more drastic with the hexahydrate form, as it has six (6)
waters added.
Note: Bound water is signified by a "dot"
between the chemical formula for the substance and the number of
waters bound. For example, the dihydrous form of calcium
chloride: CaCl2.2H2O
There are also different grades of purity on the market. While
each person must decide for himself how much impurity they can
tolerate, beware of phosphates and copper especially. Buying
cheaper grades of chemical may seem great at first, but can be
the root cause of inexplicable algae blooms or invertebrate
die-offs.
Again, this was not
meant to make chemists out of anyone. If it has piqued your
interest in the subject, please refer to any number of good
general chemistry books, such as the one from Charles E.
Mortimer.
This was the first part of three part
series on making one's own trace element additives. The next
installment will have the actual "cook book recipes"
for the solutions and their approximate dosages.
Part II: Inorganic
Substances as Additives in the Marine Aquarium
Part III: Inorganic Substances as Additives in the Marine Aquarium