Factors affecting the conductivity of water
Electrical conductivity is the property of water to conduct
electricity from an area of high electric field to an area of low electric
field, with the help of dissolved ions that act as conductors. An ion is an
atom that is freed from an element and carries either a positive charge or a
negative charge. Although metals are far more effective conductors, water also
has the ability to conduct electricity. There are several factors that affect
the electrical conductivity of water, such as TDS (Total Dissolved Solids, or
concentration of salts in water), mineral purity and temperature of water.
Factors that affect
the conductivity of water
Total Dissolved Solids (TDS) / Salinity
Salt water conducts electricity much effectively and more
readily than pure water. Since dissolved ions enhance salinity as well as
increase conductivity, it is routinely used to calculate electrical
conductivity. Salts ions that usually cause salinity are sulphates, carbonates,
chlorides, potassium, sodium, calcium and magnesium. Electrical conductivity
will change with the kind of water source – groundwater, runoff water, water
drained from agricultural fields and rainfall. Therefore, sub-factors such as
geology, soil, land use and flow of water (conductivity increases as water flow
decreases) also affect the salinity of water, thus influencing electrical
conductivity.
Mineral purity
The electrical conductivity of pure water is low, but it can
be greatly increased by soluble impurities that will ionize in water (such as
common salt). Pure water consists of one oxygen and two hydrogen atoms. The
oxygen atoms share covalent bonding (with their outermost electron shells) with
the two hydrogen atoms, completing their octet of outermost shell. Therefore,
one oxygen atom can bond covalently with two dihydrogen molecules (two bonded
hydrogen molecules). Electricity travels easily and readily through materials
having atoms that form an ionic bond. Oxygen atoms in the water molecule pull
the electrons strongly, thereby developing a negative charge. The dihydrogen
forms a positive charge, thus resulting into negligible transfer of electric
flow. If minerals as impurities are added in water, the ionic bonds conduct
electricity and the electrolytic conductivity of water increases.
Temperature
Electrical conductivity in water invariably increases with
an increase in temperature, as opposed to metals. Warm water is less viscous
and has greater electronic movement, thus allowing free flow of electric
current. It is generally expressed as a relative change per degree Celsius, at
a particular temperature. Small variation or difference in temperature reports
a marked difference in conductivity and therefore, readings are normally
referenced to 25C. Generally, conductivity increases by about 2% for every degree
rise in temperature (range being 1 to 3 %).
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