Hard and Soft Water-Advanced

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Hard and soft water

Hard water: Water that contain high amout of dissolved minerls or ions such as calcium, magnesium etc.
Soft water: Soft water is surface water that contains very low concentration of ions or minerals, e.g., Rainwater and distilled water.

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Causes and types of hardness of water

Hardness of water is due to the chlorides, sulphates bicarbonates of calcium and magnesium in it.
Types of hardness of water are:

Temporary hardness
Permanent hardness

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Methods of removing temporary hardness

Temporary hardness can be removed by boiling and filtering the water.

Boiling : When temporary water is boiled, bicarbonates of calcium and magnesium decompose to form insoluble calcium and magnesium carbonates which can be easily filtered off
By clark's process:

C a O + H_{2} O \to C a (O H)_{2}

C a (H C O_{3})_{2} + C a (O H)_{2} \to 2 C a C O_{3} + 2 H_{2} O

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Methods to remove permanent hardness

Washing soda process: Hard water is treated with a calculated amount of washing soda when chlorides and sulphates of calcium and magnesium present in hard water get precipitated as insoluble calcium and magnesium carbonates which can be filtered off.

C a C l_{2} + N a_{2} C O_{3} \to C a C O_{3} + 2 N a C l

M g S O_{4} + N a_{2} C O_{3} \to M g C O_{3} + N a_{2} S O_{4}

Calgon's method: Sodium hexametaphosphate (

N_{6} P_{6} O_{18}

), commercially called 'calgon', when added to hard water , the reaction is as follows:-

N a_{6} P_{6} O 18 \to N a^{+} + N a_{4} P_{6} O_{18}^{2 -}

(M = Mg, Ca)

M^{2 +} + N a_{4} P_{6} O_{18}^{2 -} \to [N a_{2} M P_{6} O_{18}]^{2 -} + 2 N a^{+}

The complex anion keeps the

M g^{2 +}

and

C a^{2 +}

ions in solution.

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Experiments based on hard and soft water

There are two types of hardness i.e. temporary hardness and Permanent hardness. Temporary hardness is due to calcium and magnesium bicarbonates. It can be removed by boiling followed by filtration. Permanent hardness is due to the presence of chlorides and sulfates of calcium and magnesium. It can be removed by the addition of washing soda and caustic soda.

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Methods for removing both the hardness of water

Lime Soda process

C a (H C O_{3})_{2} + C a (O H)_{2} \to 2 C a C O_{3} + 2 H_{2} O

C a C l_{2} + N a_{2} C O_{3} \to C a C O_{3} + 2 N a C l

Ion exchange method: This is the most modern method for softening of hard water. $C a^{2 +}, M g^{2 +}$ ions present in hard water are exchanged by those present in complex inorganic and organic compounds.

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Removal of temporary and permanent hardness by ion exchange method

There are a number of methods to remove the hardness present in water. A few methods to remove hardness from water are,

Chemical Process of Boiling Hard Water
Adding Slaked Lime (Clark's Process)
Adding Washing Soda
Calgon Process
Ion Exchange Process
Using Ion Exchange Resins

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Removal of hardness of water

There are a number of methods to remove the hardness present in water. A few methods to remove hardness from water are,

Chemical Process of Boiling Hard Water
Adding Slaked Lime (Clark's Process)
Adding Washing Soda
Calgon Process
Ion Exchange Process
Using Ion Exchange Resins

example

Removal of hardness of water

There are a number of methods to remove the hardness present in water. A few methods to remove hardness from water are,

Chemical Process of Boiling Hard Water
Adding Slaked Lime (Clark's Process)
Adding Washing Soda
Calgon Process
Ion Exchange Process
Using Ion Exchange Resins

example

Removal of hardness of water

There are a number of methods to remove the hardness present in water. A few methods to remove hardness from water are,

Chemical Process of Boiling Hard Water
Adding Slaked Lime (Clark's Process)
Adding Washing Soda
Calgon Process
Ion Exchange Process
Using Ion Exchange Resins

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Properties of Water

Properties of water:

Water is transparent in colour.
Water has no shape,it takes the shape of vessel in which it is kept.
Water applies an upward force on every object immersed in it.
Water could dissolve many things like salt, sugar but not oil and chalk powder.
In water few objects sinks and few floats based on the heaviness and area occupied by objects.For example, a needle sinks and a heavy boat floats , this happens because boats occupies more area over water and needle occupies less area creating more push on water.

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