Water Types and its uses for std 9th GSEB CBSE Course

Hard and soft water
Experiments with hard water
Removal of hardness
Conservation of water.

Water is a wonderful substance.
It is one of our invaluable resources.
Without it life can neither exist on earth nor can the bio-chemical reactions take place.
Let us once again recall some of the important points that you have already studied about water.
Water is a compound made of hydrogen and oxygen.
Water is a compound made of hydrogen and oxygen.
Most of the land on earth is Covered with water.
Water exists on earth in all the three states – solid, liquid, and vapour.
Water can dissolve the highest number of substances in it.
Most of the substances that dissolve in water are inorganic ionic compounds.
The ionic compounds dissociate into positive and negative ions when dissolved in water.

Remember
Indian philosophers regarded water as one of the five elements that constitute the universe. Even the westerners had similar views. A British chemist, Sir Henry Cavendish showed for the first time in 1781, that water is produced when hydrogen burns in air. Lavosier, a French chemist proposed that water is not an element but a compound made of hydrogen and oxygen.
Seawater is saline and hence not potable. Distillation is a method of obtaining pure water from seawater.
Even distilled water is not potable.
Water gets cycled continually through the biosphere and this movement is called water cycle.
Water sources are being polluted due to human activities.

INTRODUCTION
The water obtained from natural sources have several salts dissolved in it.
Salts such as nitrates, sulphates, chlorides, and bicarbonates might have been dissolved in water.
Pure water has neither colour and taste nor smell.
Water gets colour, taste, and smell due to impurities.
Water acquires certain properties other than colour, taste and smell, when certain salts are dissolved in it.

Note
Rainwater 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 dissolved in it. Hence even rainwater is not pure.
The change in the way it interacts with soap is one such property.
Based on the way in which it acts with soap,

Water is classified as

Soft water, Hard water

SOFT WATER AND HARD WATER
Water that gives lather with soap easily and readily is called soft water.
Pure water is always soft.
Water may be soft even when some salts are dissolved in it.

Experiment : 1Collect samples of water from different sources – tap, bore-well, pond or lake etc.
Take equal quantity of the samples collected in different test tubes.
Add about 1 gram of soap powder to each of them.
Shake well, Which of them gave lather easily and spontaneously ?
Which sample does not give lather readily?
 

Different types of water sample for test

Test of soap leather on different types of water sample.

Experiment : 2Collect samples of water from various sources as mentioned in the experiment cited above.?
Add 1 gram of soap powder to each of them and stir until the soap dissolves in water.
Now blow the contains of each of the test tubes using a stir few times.
Which of them gives lather profusely?

Different types of water sample for test

Blow Air test on water with soap.

Experiment : 3Does the water you use at home give lather readily with soap? Test and find out.


Experiment : 4Take equal quantities of water in two beakers.
Add about 1 gram of calcium chloride to one of them and stir well.
Now add about 1 gram of soap powder to each beaker.
Blow the contents of the beakers using a straw.
Which of them give lather well ?
Repeat the experiment by using sodium chloride, sodium bicarbonate, magnesium chloride, calcium sulphate, and magnesium sulphate instead of calcium chloride.
Which of them give lather ?
Which of them does not give lather ? Examine.

Test of water with different chemicals.

Certain salts dissolved in water from a scum with soap.
Water that forms an insoluble scum with soap before giving lather is called hard water.
Hard water does not readily give lather with soap.
The dissolved salts such as calcium bicarbonate, calcium sulphate, calcium chloride, magnesium bicarbonate, magnesium sulphate and magnesium chloride are the chief salts that cause hardness of water.
Let us consider how these salts render water hard.
Remember
It is not practically possible to obtain calcium bicarbonate and magnesium bicarbonate in solid form. This is because these salts chemically dissociate much before the evaporation is complete and form their respective carbonates. Therefore, it is only possible to have solutions of calcium bicarbonate and magnesium bicarbonate.

Note that the salts that cause hardness are ionic compounds.
These salts ionize to give positive ions and negative ions when dissolved in water.
For example, magnesium sulphate when dissolved in water, dissociates into Mg++ ions and SO₄- ions.
Similarly calcium sulphate (CaSO₄) dissociates into Ca++ and SO₄-.
The equations showing the process of ionization of salts causing hardness of water, are given below.

Process of Ionization of Salts.

Remember
calcium fluoride and salts of iron. Lons of iron and manganese The salts that cause hardness in water include will also cause hardness of water.
Of the ions mentioned above, only Mg⁺⁺ and Ca⁺⁺ ions cause hardness.
These ions form an insoluble scum with soap.
How does hard water form scum with soap ?
Soap (you will know more about it later) is a sodium salt or potassium salt (Ex: sodium stearate or potassium stearate respectively).
These salts react with Mg⁺⁺ and Ca⁺⁺ ions present in water to form magnesium stearte and calcium stearate respectively.
These insoluble precipitates, from a scum on the surface of contact.
Soap begins to give lather only after all the Mg⁺⁺ and Ca⁺⁺ ions present in this water samples are precipitated.