WATER
 The Universal Solvent
 Introduction
1
19.1
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Water is colourless. Water has no smell. It is odourless.
Water is tasteless . Water is shapeless .
• Water is the most common substance found on the Earth.
About 3/4 th of the Earth is covered with water.
• Water can be found in ponds, rivers, lakes, oceans and
seas.
• Water acquires certain properties when certain salts are
dissolved in it .
2
• In this chapter we will be learning
about :
•
•
•
•
•
•
Soft and Hard water
Experiments with Hard
Types of Hardness
Disadvantages of Hardness
Removal of Hardness
Conservation of Water
3
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•
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Less than 1% of the water supply on earth can be used as
drinking water.
By the time a person feels thirsty, his or her body has lost
over 1 percent of its total water amount
When water contains a lot of calcium and magnesium, it is
called hard water. Hard water is not suited for all purposes
water is normally used for
4
5
HARD WATER AND
SOFT WATER
 Soft water-Water that gives lather
with soap easily and readily is
called Soft water.
•
Hard water- Hard water
forms scum when it comes in contact with water.
IS RAIN WATER PURE??
 No, Because Rain water dissolves small amount of
atmospheric carbon dioxide in it to form a weak acid
called carbonic acid .The other chemicals that are let
into the atmosphere may also be dissolved.
HARD WATER
 Hardness of water is due to presence of dissolved salts
such as bicarbonates, sulphates, chlorides of
magnesium and calcium.
Let us consider how
these salts render water
hard..
RESULTS FOR TESTS ON
HARD AND SOFT WATER
LETS SEE HOW THIS
HAPPENS!!
http://www.youtube.c
om/watch?feature=pl
ayer_detailpage&v=41
eBQ9_FFV4
SCUM FORMATION
 After ionization Mg++ and Ca++ cause hardness.
These ions form an insoluble scum with soap. How??
 Soap is a potassium stearate or sodium stearate these
salts reacts with Mg++ and Ca++ to give Scum.
scum
HARDNESS OF WATER
PERMANENT HARDNESS:
The hardness caused by dissolved
Magnesium chloride, calcium chloride,
magnesium sulphate or
calcium sulphate is called
permanent hardness.
TEMPORARY HARDNESS:
The water that contains bicarbonate ions along with
Mg++ and Ca++ ions could be softened by mere
boiling. Hence, such water is called temporary hard
water.
DISADVANTAGES OF HARD
WATER
WHAT HAPPENS WHEN
HARD WATER IS USED??
Makes the skin dry and leaves a
whitish residue on the skin. The
utensils lose shine and get stained
when washed with hard water
The utensils lose shine and get
stained when washed with hard
water
SCALE FORMATION:
 Hard water contains
dissolved bicarbonates.
 The dissolved
bicarbonates, on boiling,
dissociate to form
insoluble carbonates
which go on depositing
on the inner walls of the
boiler.
 This results in “scaling”.
LETS SEE WHAT
HAPPENS…
WHEN SOAP SOLUTION IS ADDED TO HARD WATER..
Any guess..??
https://www.youtube.com/watch?feature=player_detailpag
e&v=zQjIr_jgqtE
WHAT COULD BE THE
REMEDY??
THINK..
THINK..
Converting hard water to
soft water !!
Methods of Softening
Hard Water
 Method of Removal of Temporary Hardness
 BOILING:
 When water is
boiled, the bicarbonates that cause
temporary hardness are converted into insoluble
carbonates, leading to the removal of Ca++ and
Mg++ from water.
Calcium bicarbonate → Calcium carbonate ↓ +
Water + carbon dioxide
Ca(HCO3)2 → CaCO3↓ + H2O + CO2
(Aqueous) → (solid) (liquid) (gas)
Magnesium bicarbonate→ Magnesium carbonate↓ +
Water + carbon dioxide
Mg(HCO3)2 → MgCO3↓ + H2O + CO2
(Aqueous)
(solid) (liquid) (gas)
 The precipitates that are formed are removed by
filtering.
 Reasons to consider other methods of softening:
 Boiling is the easiest method of softening a small
quantity of water.
 Softening a large quantity of water by boiling is
highly expensive. The process is also time
consuming.
 Temporary hardness is rare.
 Boiling removes the bicarbonate component only.
 Methods of removal of permanent hardness
 DISTILLATION:
 Principle:
The condensation of water vapours
produced on heating.
 This method removes both temporary and
permanent hardness.
 Distilled water is both soft and pure.
Youtube link:
www.youtube.com/watch?v=xxNfJLMNS4E
DISTILLATION APPARATUS
 SODA PROCESS:
 Both
temporary hardness and permanent
hardness of water can be removed by adding
sodium carbonate.
 Sodium carbonate reacts with salts that cause
hardness to give their respective carbonates.
CaSO4 + Na2CO3 → CaCO3↓ + Na2SO4
MgSO4 + Na2CO3 → MgCO3↓ + Na2SO4
CaCl2 + Na2CO3 → CaCO3↓ + 2NaCl
MgCl2 + Na2CO3 → MgCO3↓ + 2NaCl
Ca(HCO3)2 + Na2CO3 → CaCO3↓ + 2NaHC
 The
insoluble carbonates present in the softened
water are removed by filtration.
 The water softened by this method contains salts
such as sodium sulphate, sodium chloride and so
on.
 These salts do not come in the way of formation of
lather with soap.
 PERMUTIT PROCESS:
 This
method removes both temporary hardness
and permanent hardness.
 Naturally occurring sodium aluminium silicate is
called Zeolite.
 Artificially prepared sodium aluminium silicate is
called permutit.
 Permutit is prepared by heating quartz, sand,
china clay and sodium carbonate.
 Fusing sodium silicate and sodium aluminates is
another method of preparing permutit.
 Permutit is in the form of a porous gel.
 Principle:
1.
2.
3.
4.
To convert the dissolved salts of calcium and
magnesium into insoluble calcium and
magnesium permutits, respectively.
This is done by exchanging the base ion radicals
such as Ca++ and Mg++ with the base ion Na+
of sodium aluminium silicate.
Hence this process is also known as ‘base
exchange process’.
This is carried out by passing hard water
through the layers of zeolite or permutit.
 There will be a column in which




gravel, sand and permutit are placed
in alternate layers.
Hard water is made to rise up
through the various layers.
As water passes through the
permutit, the ions of calcium (Ca++)
and magnesium (Mg++) which cause
hardness are exchanged with the
sodium ions of the permutit.
Due to this exchange, the sodium
ions of the permutit is changed
eventually into calcium aluminium
silicate and magnesium aluminium
silicate.
These are called calcium permutit
and magnesium permutit
respectively.
Sodium permutit + Calcium chloride → Calcium
permutit + Sodium chloride
Na2Pm + 2CaCl2 = CaPm +NaCl
Sodium permutit + Magnesium sulphate →
Sodium sulphate+ Magnesium permutit
Na2Pm + MgSO4 = Na2SO4 + MgPm
The water softened by this method contains sodium
ions. The presence of these ions will not make water
hard.
What we get through permutit process is only soft
water and not pure water.
 Advantages:
Permutit process is an economical
way of softening water. The hardness is more or
less completely removed by this method.
 Disadvantages: This method is not appropriate if
the hard water contains
1.
sodium salts or suspended matter in large
quantities.
2. Lead.
3. iron or manganese impurities.
9.6 CONSERVATION
OF WATER
What is conservation of water?
 The effort made by the society towards the rational
use, prevention of pollution and of water is called
water conservation.
Why do we need to conserve water?
 Water appears to be abundant source. This has led to
abuse of water. Although more than 75% of the surface
of the earth is covered with water, the water that is fit
and available for our consumption is very much less.
Therefore we need to conserve water.
Let us study about distribution of water on earth
Distribution of water on
earth
Distribution of water on earth(in
percentage)
Ocean and salt lakes
Ice
Atmospheric vapour
Rivers
Ground water
Ponds/lakes
97.3
2.0
0.7
 97% of the earth’s water is salt water which is unfit to
drink
 2% is in the frozen form
 Only 1% is fresh water-fit to drink
That needs to be enough for every one-all 7 billion
of us
 70% of all fresh water is in form of ice and snow,
nearly 30% is in soil or underground. Rivers and lakes
make up just 1% of all earth’s fresh water
 There is serious water crisis in our world right now.
Nearly 1 billion people live without drinking water.
 1 out of every 8 people on earth search for clean water
every day. 1 in 6 has no access to toilet. Think about
that. What would be your life like, if that were you?
 Every 20 sec a child die from water related disease.
4000 child die every day
How much longer can we let this go,this can not
last for ever.This needs a solution.
SAVE water, CONSERVE water
There are many causes for the scarcity of water. Some of
these are listed below:
 Ever increasing population
 Unsatisfactory management of water
 Deforestation and soil erosion
 Inadequate storage facilities
 Pollution of water
 Growing crop-breeds that consume more water
 Overuse of ground water
 Wastage through leakage, absorption, and
evaporation.
 Lowering of the storage capacity of water
 bodies due to silt collection.
 Wasteful habits of using water.
Click on link below
http://www.youtube.com/watch?v=BCHhwxvQqxg
http://www.youtube.com/watch?v=_9OGvcVA3Gw
http://www.youtube.com/watch?v=GlWVDcdRVUA