19.1 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
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3 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
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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
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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.
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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.
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HARD WATER Hardness of water is due to presence of dissolved
salts such as bicarbonates, sulphates, chlorides of magnesium and
calcium.
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Let us consider how these salts render water hard..
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RESULTS FOR TESTS ON HARD AND SOFT WATER
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LETS SEE HOW THIS HAPPENS!! http://www.youtube.c
om/watch?feature=pl ayer_detailpage&v=41 eBQ9_FFV4
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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
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HARDNESS OF WATER PERMANENT HARDNESS: The hardness caused by
dissolved Magnesium chloride, calcium chloride, magnesium sulphate
or calcium sulphate is called permanent hardness.
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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.
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DISADVANTAGES OF HARD WATER
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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
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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.
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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
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WHAT COULD BE THE REMEDY?? THINK.. Converting hard water to
soft water !!
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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)
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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.
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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
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DISTILLATION APPARATUS
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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
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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.
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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.
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Principle: 1. To convert the dissolved salts of calcium and
magnesium into insoluble calcium and magnesium permutits,
respectively. 2. This is done by exchanging the base ion radicals
such as Ca++ and Mg++ with the base ion Na+ of sodium aluminium
silicate. 3. Hence this process is also known as base exchange
process. 4. This is carried out by passing hard water through the
layers of zeolite or permutit.
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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.
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Sodium permutit + Calcium chloride Calcium permutit + Sodium
chloride Na 2 Pm + 2CaCl 2 = CaPm +NaCl Sodium permutit + Magnesium
sulphate Sodium sulphate+ Magnesium permutit Na 2 Pm + MgSO 4 = Na
2 SO 4 + 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.
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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.
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9.6 CONSERVATION OF WATER
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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
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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
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97% of the earths 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 earths fresh
water
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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
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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.
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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=_9OGvcVA3Gw
http://www.youtube.com/watch?v=BCHhwxvQqxg
http://www.youtube.com/watch?v=GlWVDcdRVUA