Water
is said to be hard if cannot readily form a lather with soap. This is as a
result of mineral salts present in the water. The principal minerals
responsible for hardness of water are:
is said to be hard if cannot readily form a lather with soap. This is as a
result of mineral salts present in the water. The principal minerals
responsible for hardness of water are:
a) Calcium carbonate
b) Calcium sulphate
c) Magnesium carbonate and
d) Magnesium sulphate
Types of hardness in water
There
are three types of hardness in water. They are:
are three types of hardness in water. They are:
i. Temporary hardness: this is due to the
presence of bicarbonates of calcium and magnesium.
presence of bicarbonates of calcium and magnesium.
ii.
Permanent
hardness: this is due to the presence of sulphates and chlorides of calcium and
magnesium. This hardness is still present even after boiling.
Permanent
hardness: this is due to the presence of sulphates and chlorides of calcium and
magnesium. This hardness is still present even after boiling.
iii.
Combined
hardness: this is due to the presence of both bicarbonate, sulphate, chlorides
and magnesium in the same water at the same time.
Combined
hardness: this is due to the presence of both bicarbonate, sulphate, chlorides
and magnesium in the same water at the same time.
Effect
of hard water
of hard water
i.
It
wastes soap into excess
ii.
It
spoils plumbing materials
iii.
It
spoils cooking utensils and films or spots on material surfaces.
iv.
It
renders food less digestible and food does not cook well
v.
It
is dangerous for generation of stream as they precipitate inside the boilers
and may lead to explosion or bursting due to overheating (because more energy
would be required to raise the temperature).
How to remove hardness in water
1.
Temporary
hardness:
Temporary
hardness:
a)
By
boiling, carbon dioxide is expelled and calcium carbonate or magnesium
carbonate is precipitated
By
boiling, carbon dioxide is expelled and calcium carbonate or magnesium
carbonate is precipitated
b)
Addition
of lime CaOH and calcium carbonate is obtained.
Addition
of lime CaOH and calcium carbonate is obtained.
2.
Permanent
hardness:
Permanent
hardness:
a)
By
distillation (not ordinary boiling) turn the liquid into vapour by heating,
cool the vapour and collect drops of liquids that condense from the vapour.
By
distillation (not ordinary boiling) turn the liquid into vapour by heating,
cool the vapour and collect drops of liquids that condense from the vapour.
b)
Addition
of lime and soda (Na2Co3) from a harmless precipitate
known as sulphate of soda. This method removes dissolved impurities, water then
becomes alkaline and should be neutralized with carbondioxide and sulphuric
acid (tetraoxosulphate VI acid) H2SO4
Addition
of lime and soda (Na2Co3) from a harmless precipitate
known as sulphate of soda. This method removes dissolved impurities, water then
becomes alkaline and should be neutralized with carbondioxide and sulphuric
acid (tetraoxosulphate VI acid) H2SO4
iii)
Combined hardness:
Combined hardness:
(a)
Addition of both milk of lime and caustic soda
from a precipitate of carbonates and sulphates, this is known as Base Exchange
process. In this method the water is filtered through a filter of sodium zeolite
or a synthetic ion exchange resin here, the sodium is exchanged for calcium and
magnesium (ca and mg). The water thus obtained contains sodium chloride. To
remove sodium chloride, the water has to be filtered through another column
containing ion exchange resin.
Addition of both milk of lime and caustic soda
from a precipitate of carbonates and sulphates, this is known as Base Exchange
process. In this method the water is filtered through a filter of sodium zeolite
or a synthetic ion exchange resin here, the sodium is exchanged for calcium and
magnesium (ca and mg). The water thus obtained contains sodium chloride. To
remove sodium chloride, the water has to be filtered through another column
containing ion exchange resin.
(b)
Filtration through a process called “permutit”.
Filtration through a process called “permutit”.
