Some useful chemicals

chemicals || hard water || soft water || some useful chemicals || advantages and disadvantages of hard and soft water

1. What is water? What is the importance of water in human life?
Ans: Water is compound made of hydrogen and oxygen in the ration of 2:1. Water is most common substance on the earth. Water is important in human life due to following reasons:

1. It is used for drinking.
2. It is used for bathing, washing and cleaning purpose.
3. Water is used for irrigational purpose.

2. How does rainfall takes place? Explain.
Ans: When the extreme heat of the sun fall on sea water. The water get evaporated. The evaporated water vapour is taken to long distances by the wind and it becomes cloud due to condensation of water vapour. The cloud contains water droplets along with frozen vapour at high altitude which acts as big piece and collides with the Himalayas. Duee to collision, water in the form of ice begins to shake and melts so that it begins to fall down in the form of rain. In this way rainfall takes place. The rain water gets soaked into the soil and comes out as springs and rivers. The deposited water in underground may be obtained from wells.

3. Write down the physical properties of water.
Ans: The following are the physical properties of water;

1. Water is colourless, odourlesss and transparent liquid.
2. Water exists in three states- solid (ice), liquid (water) and gas (steam).
3. Water freezes at O^oC and boils at 100^oC at normal atmospheric pressure.
4. Its density is 1g/cm³ at 4^C.
5. Pure water is a bad conductor of head and electricity.
6. It can dissolve many substances.

4. Why is water called a universal solvent?
Ans: Water can dissolve many substances and hence called a universal solvent.

5. Write any two chemical properties of water.
Ans: The followig are the chemical properties of water;

1. It is formed by combining two parts of hydrogen and one part of oxygen.
2. Water is neutral substance.

6. Define soft water and hard water.
Ans: Soft water: Soft water is the one which can produce lather with soap easily.
Hard water: Hard water is the one which can't produce lather with soap easily.

7.What makes water hard?
Ans: The soluble salts of calcium and magnesium make the watrer hard.

8. Write the advantages of hard water.
Ans: The following are the advantages of hard water:

1. Hard water contains calcium salt dissolved in it which helps to strengthen the bones and teeth.
2. Water is somewhat tasty due to dissolved salts of calcium and magnesium.
3. Hard water is used in beer industries.

9. Write the disadvantages of hard water.
Ans: The disadvantages of hard water are as follows:

1. Hard water lead sto consume more soap while washing clothes.
2. A bright white cloth becomes dull due to salts dissolved in water.
3. In industries, due to hard water, the life of boilers decreases. This is due to the calcium salt deposited during boiling.

10. The taste of boiled water is different from original water, why?
Ans: If water is boiled, its temporary hardness of water is lost. This means some soluble salts become insoluble. So, the natural taste of water is lost. 

11. Distinguis between soft water and hard water.
Ans: The differences between soft water and hard water are as follows:

Soft water	Hard water
It doesnot conatin soluble salts of magnesium and calcium.	It contains soluble salts of magnesium and calcium.
It forms lather easily with soap.	It doesnot form lather easily with soap.

12. Decribe briefly the process of making temporary hard water soft.
Ans: Temporary hardness in water is caused due to the dissolved calcium and magnesium bicarbonate. This hardness can be removed by following process:

1. By Boiling water:
   On heating temporary hard water, the soluble salts like calcium bicarbonate and magnesium bicarbonate get changed into soluble carbonate salts and these settle down to the bottom of the container and can be filtered away.
   For example: Calcium bicarbonate -----------------Calcium carbonate + Carbondioxide + water
   Magnesium bicarbonate --------------- Magnesium carbonate + carbondioxide + water
2. By adding slaked lime [(Ca(OH)₂]
   Temporary hardness of water can also be removed by adding slaked lime.
   For example:
   Calcium bicarbonate + Calcium hydroxide ---------- Calcium carbonate + water
   Magnesium bicarbonater + calcium hydroxide --------- Calcium carbonate + Magnesium hydroxide + water

13. Describe briefly the process of making permanent hard water into soft.
Ans: Permanent hardness in water is due to dissolved calcium chloride, magnesium chloride, calcium sulphate and magnesium sulphate. The permanent hardness can be removed by the following methods.

1. By treating hard water with washing soda:
   In this process, following reaction takes place and water becomes soft.
   Calcium chloride + washing soda (Na₂CO₃) ------- Calcium carbonate + sodium chloride
   Magnesium Chloride + washing soda ------------------ Calcium carbonate + Sodium chloride
   Calcium sulphate + washing soda ------------ Calcium carbonate + sodium sulphate
   Magnesium sulphate + washing soda ----------- Magnesium carbonate + sodium chloride