Permanent hardness
Permanent hardness is hardness (mineral content) that cannot be removed by boiling
. When this is the case, it is usually caused by the presence of calcium sulfate
and/ormagnesium sulfates
in the water, which do not precipitate out as thetemperature
increases. Ions causing permanent hardness of water can be removed using a water softener, or ion exchange column
.
Total Permanent Hardness = Calcium Hardness + Magnesium Hardness
The calcium and magnesium hardness is the concentration of calcium and magnesium ions expressed as equivalent of calcium carbonate.
Total permanent water hardness expressed as equivalent of CaCO3 can be calculated with the following formula: Total Permanent Hardness (CaCO3) = 2.5(Ca2+) + 4.1(Mg2+).[5]
Effects of hard water
With hard water, soap solutions form a white precipitate (soap scum
) instead of producing lather
, because the 2+ ions destroy the surfactant
properties of the soap by forming a solid precipitate (the soap scum). A major component of such scum is calcium stearate
, which arises from sodium stearate
, the main component of soap
: