NEWS104
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The importanceofwaterhardnessforthebreedingofornamentalfisheswasrealizedthankstotheHarlequinRasbora.
hardness. Thus if water contains lots of
thesecalciumandmagnesiumcompounds
thenwe have hardwater, but if it has only
small amounts of calcium andmagnesium
compounds in it thenwe have soft water.
The correct scientific expression for this is
that total hardness is the sum of all the
alkaline earth metal ions dissolved in the
water.
Alkalineearthmetal ions
The alkaline earth metals are chemical
elements. They are called beryllium (Be),
magnesium (Mg), calcium (Ca), strontium
(Sr), barium (Ba), and radium (Ra). But, in
practice,onlycalciumandmagnesium ions
occur in suchhigh concentrations inwater
that they need to be taken into
consideration. These ions have a positive
charge, and are thus cations.The negative-
charged counterparts of these alkaline
earthmetal ions - the anions – responsible
for thebiological effects of thehardness in
the water are carbonates, which are
compoundmoleculescomposedofcarbon,
hydrogen,andoxygen.
Total hardness
Totalhardnesshasalreadybeendefined: it
is the sum of all the alkaline earthmetal
ion concentrations in the water. It is
termed total hardness because it ismade
up of two components, the carbonate
hardness
and
the
non-carbonate
hardness. These two terms will be
explained
shortly.
Calcium
and
magnesium are very important for the
body; they are the reason we drink
mineral water, which contains verymany
of these cations. These alkaline earth
metal cations form water-insoluble
compounds (soap precipitates) with the
wash-active components of soap, the
tensides, but the precipitates have no
cleaning power of any kind. The tensides
in soap are anionic. This is why so much
more soap is required inhardwater.
Carbonatehardness
The carbonate hardness is the part of the
total hardness that is formed by the
bicarbonate anions. (From a chemical
viewpoint that is incorrect,as in fact some
of the cations that in total make up the
hardness are those of calcium and
magnesium,but inpractice this iswithout
significance, as the two metal ions are
equivalent to the bicarbonate ions
present).Bicarbonate is inequilibriumwith
Infobox
What isan ion?
Apple users might think it was a
brilliant new invention from the
ideas melting-pot of Steve Jobs.
However, it isn’twritten i-On,but ion,
and is nothing more than an
electrically-charged particle - atom
or molecule – that has acquired
additional electrons or lost some of
the electrons originally present,
thereby achieving a chemically
stable condition. If an ion has lost
electrons and thereby acquired a
positive charge, then it is termed a
cation, while if it has a negative
charge as the result of acquiring
additionalelectrons,then it is termed
an anion. A well-known example:
why does common salt (NaCl,
sodium chloride) dissolve in water?
Chemically speaking, common salt
consists of a combination of
positively-charged sodium ions and
negatively-charged chlorine ions. If
common salt is added towater, then
water molecules combine with the
positively-charged sodium ions and
negatively-charged chlorine ions.
Water (H2O) possesses a positive
charge from its hydrogen (H), and a
negative charge from its oxygen (O).
Likemagnets, positive and negative
chargesareattracted tooneanother.
As long as there are sufficient water
molecules then they will combine
with the ions of the common salt,
and so the salt dissolves. But sooner
or later the solution becomes
saturatedand it isno longerpossible
to dissolve more salt: it trickles
undissolved to the bottom of the
container inwhich theexperiment is
being conducted. Energy is required
to dissolve salt in water, and hence
the solutioncoolsdown.
AltumAngel,a typical softwater fish.
