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Re: Temp Hardness vs permanent hardness was DYING SNAILS
At 09:23 AM 7/21/2002 -0500, you wrote:
>Temporary hardness in due to Calcium Bicarbonate while permanent hardness
>is due to the amount of Carbonate present in the water.
I think this is a typo, Charles. So called permanent hardness is a measure
of dissolved calcium ions in the water. Temporary hardness, as you state,
is a measure of calcium bicarbonate. The latter is also referred to as
alkalinity and buffering capacity.
Actually, that is a simplification, but serves to understand the
principles. The term hardness comes from the old days of using real soaps,
which are potassium and sodium salts of fatty acids (such as oleic acid).
Soap used to be made by boiling animal fat (lards) in water with wood
ashes. The latter are high in potassium, resulting, under these hydrolyzing
conditions, in the formation of potassium hydroxide ("potash") and fatty
acids. These salts are soluble in water, and act as detergents, which are
able to emulsify fats and oils in water. That is why they work to remove
"dirt". Salts of fatty acids with calcium, magnesium, iron and others
cations are insoluble. Thus, if you try to wash with a real soap in water
containing a lot of those ions, the soluble soaps will be precipitated as
calcium, magnesium, iron (etc) salts, which are insoluble. Thus the water
won't lather easily, and thus the term "hard water". Incidentally, modern
"soaps" are not soaps at all, but synthetic detergents, which don't have
these problems to the same degree.
In those good old days hardness of water could be reduced in several ways,
but it was typically done by adding washing soda, which is sodium
carbonate. As calcium carbonate is insoluble, this treatment precipitates
the calcium, thus removing the source of calcium ions, which no longer can
interact with the soaps. Thus, that treated water would be high in
carbonates, but "soft' because the calcium would have been precipitated out.
I said alkalinity, or buffering capacity, is equivalent to temporary
hardness. That is not quite true, either. Sodium or potassium bicarbonate
in water will provide buffering capacity and alkalinity, but would not
contribute to hardness. However, in "real" water, addition of sodium
bicarbonate in the presence of calcium ions would result in an equilibrium
in which you essentially have calcium bicarbonate in solution.
To summarize and simplify again:
Hardness, also known as permanent hardness or calcium hardness, is due to
the presence of calcium ions (mainly) as well as magnesium, iron and other
ions in the water.
Temporary hardness, also known as alkalinity or buffering capacity, is due
to the presence of calcium bicarbonate in the water. Untreated, these
calcium ions would also make the water "hard". In other words, true soaps
would not lather. When the water is boiled, CO2 is driven off, resulting in
calcium carbonate, which is precipitated (as "sclae"), thus softening the
water. In other words, this form of hardness is "temporary".
I hope this, with the historical perspective, will help to clarify a set of
terminology that aquarists, for good reasons, always find confusing.
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