In hard water, lather is very difficult to form, leather is not formed in hard water.

A temporary hard water can from lather with soap. The ${ Ca }^{ 2+ }/{ Mg }^{ 2+ }$ ions of water displace ${ Na }^{ + }$ or ${ K }^{ + }$ ions from this salts & form insoluble $Ca/Mg$ salts of fatty acids. 

Soft water is surface water that contains low  concentrations of ions and in particular is low in ions of calcium and magnesium. Soft water naturally occurs where rainfall and the drainage basin of rivers are formed of hard, impervious and calcium poor rocks.

Hard water is water that has high mineral content (in contrast with "soft water"). Hard water is formed when water percolates through deposits of limestone and chalk which are largely made up of calcium and magnesium carbonates. Hard drinking water may have moderate health benefits, but can pose serious problems in industrial settings, where water hardness is monitored to avoid costly breakdowns in boilers, cooling towers, and other equipment that handles water.

Permanent hardness is caused by the presence of sulfates of $Ca/Mg$. Which further increases the hardness on boiling because boiling removes only water in the form of vapour while none of its mineral content boil away-they remain in the vessel.

Hard water does not lather with but instead forms a gooey mass called scum. Hard water is formed when water percolates through deposits of limestone and chalk which are largely made up of calcium and magnesium carbonates.

Boiling hard water with washing soda removes permanent hardness which removes ${ Ca }^{ 2+ }$ or ${ Mg }^{ 2+ }$ ions in a precipitation reaction.

Hardness of water can be of two types temporary and permanent hardness. Temporary hard water contains only bicarbonates of magnesium and calcium. It can be removed by boiling. Such water on treating with soap lathers easily.

Hardness of water can be of two types temporary and permanent hardness. Temporary hard water contains only bicarbonates of magnesium and calcium. It can be removed by boiling. Permanent hard water contains chlorides and sulfates of calcium and magnesium. It can be removed by adding washing soda.

Soaps are not suitable when hard water is used. Detergents can be used with both hard and soft water. Detergents are more soluble in water than soaps. They also have a stronger cleansing action than soaps. Detergents don't need expensive vegetable oil for their preparation as they can be prepared from hydrocarbons of petroleum. They can be used in acidic solutions whereas soaps cannot be used (free fatty acids are precipitated).

Soft water is surface water that contains low concentrations of ions and in particular is low in ions of calcium and magnesium. Because soft water has few calcium ions, there is no inhibition of the action of soaps and no soap scum is formed in normal washing. It lathers easily with water. Similarly, soft water produces no calcium deposits in water heating systems.

An easy way in which water manifests its hardness is scaling i.e. forming deposits through calcification that clog plumbing. These scales are usually white because calcium and magnesium are the most common sources of hardness in water. In swimming pools, a cloudy or milky appearance characterizes hard water.

Hardness of water can be of two types temporary and permanent hardness. Permanent hard water contains chlorides and sulphates of calcium and magnesium. It can be removed by adding washing soda.

Soap is the sodium and potassium salt of organic fatty acid. Soap reacts with hard water forming scum. They are derived from the treatment of tryglycerides with a strong base (saponification). Soaps are made by rendering fats from animal sources.

Detergents are soap-like compounds which are used for cleaning purpose. They are sodium salts of long chain alkyl benzene sulphonic acids or sodium salts of long chain alkyl hydrogen sulphate, whereas, soaps are sodium salts of long chain carboxylic acids.

Permanent hard water can be made soft by adding sodium carbonate (also called washing soda) to it. This will soften both temporal and permanent hardness. In this chemical reaction, the calcium and magnesium ions react with sodium to form a precipitate.

Water which gives lather with soap easily is called as soft water.

Calgon is a trade name of a complex salt, sodium hexametaphosphate $(NaPO _3) _6$.

$CaCO _3$ is not present in the clear water. It attains the temporary hardness to the water.

The substance that is not a water softener $MgCl _2$, which is responsible for permanent hardness of water.

Answer:- (B) An ion exchanger

Sodium hexametaphosphate $(NaPO _3) _6$, is known as calgon.

$1$ mole $CaCl _2\equiv 1$ mole $CaCO _3\equiv 1$ mole $MgCl _2$

By boiling : - On boiling, soluble $Mg{ \left( HC{ O } _{ 3 } \right)  } _{ 2 }$ is converted to insoluble $Mg{ \left( OH \right)  } _{ 2 }$ and $Ca{ \left( H{ CO } _{ 3 } \right)  } _{ 2 }$ to insoluble ${ CaCO } _{ 3 }$. It is because high solubility of $Mg{ \left( OH \right)  } _{ 2 }$ as compared to $Mg{ CO } _{ 3 }$, than $Mg{ \left( OH \right)  } _{ 2 }$ is precipitated. Precipitates can be removed by filtration.

Permanent hardness of water can be removed by permutit process. Permutite is an artifical zeolite used for softening of water. Through ion-exchange process, here cation-anion exchange chamber is used to obtain pure water. In calgon's process sodium hexa meta phosphate is used to soften the water.

Hard water contains minerals specifically $Ca,Mg$ and $Fe$ which can dry our skin and cause flaking and itching.

If density of water $=1\text{ }g/ml$

The hardness of water due to ${ HCO } _{ 3 }^{ 21 }$ is $122ppm$. Because the hardness of water in terms of ${ CaCO } _{ 3 }$ is $200$ $ppm$.

• Temporary hardness is caused by dissolved calcium or magnesium hydrogencarbonate.
  

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

Determination of hardness of water:

Determination of hardness of water is done by titration method using the technique of complexometric titration.    

Ethylenediamine tetra-acetic acid and its sodium salts (EDTA) form a chelated soluble complex when it is titrated against a solution containing certain metal cations that cause hardness to water.

Calcium sulfate $\left( CaS{ O } _{ 4 } \right) $ being less soluble in water causes permanent hardness in water.

Hard water, water that contains salts of calcium and magnesium principally as bicarbonates, chlorides, and sulfates. Water hardness that is caused by calcium bicarbonate is known as temporary, because boiling converts the bicarbonate to the insoluble carbonate; hardness from the other salts is called permanent.

Causes

Hardness (in ppm)=$\cfrac {Weight\quad of\quad Na _2CO _3\quad required\quad (in\quad mg)}{Volume\quad of\quad Hard\quad water\quad (in\quad L)}$

Temporary hardness is amount of $ CaCO _{3} $ in grams present in $ 10^{6}\,ml/grams $ of water

According to the given reaction 

The following salts may be dissolved in water to obtain hard water for the experiment
2. Calcium sulphate
3. Magnesium chloride
5. Calcium chloride

Both temporary and permanent hardness in water is removed by distillation. Temporary hardness can be removed by boiling and filtration. Permenant hardnesscan be removed by: (1) adding washing soda, (2) permutit method (3) by using ion exchange resins.

Temporary hardness is removed by boiling water with $NaOH$ and $Na _2CO _3$. $Ca(HCO _3 ) _2+2NaOH \rightarrow CaCO _3 \downarrow +Na _2CO _3+2H _2O$ Permanent hardness is removed by boiling water with sodium carbonate. $CaCl _2+Na _2CO _3 \rightarrow CaCO _3 \downarrow + 2 NaCl$

Calgon is an industrial name given to sodium hexametaphosphate. Its formula is $Na _{2}[Na _{4}(PO _{3}) _{6}]$.

The temporary hardness of water can be removed by boiling. $Ca(HCO _3) _2 \xrightarrow {boil} CaCO _3 \downarrow + CO _2 \uparrow + H _2O$.

Yes the exhausted permutit is regenerated by treating sodium hydroxide solution in Clark's method for removing permanent hardness.

Calgon is $(Na _6P _6O _{18})$ i.e. sodium hexa-metaphosphate. The calgon when added to hard water forms a  soluble complex.

Due to anomalous expansion of water the density of water is not same at all temperatures. When water is cooled from room temperature it first contracts in volume and becomes increasingly dense as do other liquids but at $4^oC$ water reaches maximum density.

Calgon is an artificial zeolite, zeolites contains Na and Al which softens the hard water.

In anoin exchange resin the reaction takes place as

${ MgHCO } _{ 3 }$ and ${ MgCO } _{ 3 }$; with the presence ${ MgHCO } _{ 3 }$ or ${ MgCO } _{ 3 }$, water becomes temporary hard. 

By boiling, the bicarbonates undergo decomposition to form insoluble carbonates of $Ca/Mg$ which can further be removed by filtration.

Temporary hardness is caused due to the presence of ${ Ca }^{ 2+ }/{ Mg }^{ 2+ }$ bicarbonates and carbonates.

Calcium bicarbonate in water is responsible for temporary hardness and not permanent hydrolysis.

Permanent hardness is due to the presence of sulphate or chloride salts of $Ca$ or $Mg$.

Hardness of water can be removed by the following two methods:
CLARK'S METHOD 
In Clarks method a calculated amount of calcium hydroxide $Ca (OH) _2$ is added to hard water. Due to reaction, insoluble carbonates are obtained which are separated by filtration.
$Ca(HCO _3) _2 + Ca(OH) _2 2CaCO _3 + 2H _2O$
$Mg(HCO _3) _2 + Ca(OH) _2 CaCO _3 + MgCO _3 + 2H _2O$
ION-EXCHANGE METHOD
In this method sodium zeolite is used as ion-exchanger. Na-zeolite is passed through the pipes containing    hard water. Sodium zeolite is converted into calcium-zeolite or magnesium-zeolite. These are insoluble in water and are separated from water by filtration.
$Ca+2 + Na2-zeolite Ca-zeolite + 2Na+1$
$Mg+2 +Na2-zeolite Mg-zeolite + 2Na+1$

Temporal hard water is caused by calcium bicarbonate. This hardness can be removed by just boiling the water, as this converts the carbonate to insoluble carbonate (This leaves a precipitate and can clog your boiler). 

If the hard water has ferrous irons (oxidized to the ferrous form) it may leave some reddish brown stains on your clothing after laundry, or on the bathroom enamel surfaces.

Calgon $\rightarrow { Na } _{ 6 }{ P } _{ 6 }{ O } _{ 18 }\rightarrow { Na } _{ 2 }\left[ { Na } _{ 4 }{ \left( { PO } _{ 3 } \right)  } _{ 6 } \right] $ it is used as water softener, when added to hard water following reaction takes place :

Soft water gives lather with soap immediately whether the hard water does not produce lather with soap.

The density of water is maximum at $4^oC$ and hence its volume at this temperature is minimum.

Hardness of water is mainly due to the dissolved salts of calcium and magnesium.

The dissolved salts in hard water do not let the pulses cook easily.

The carbonate ions from sodium carbonate react with the calcium and magnesium ions in the water to produce insoluble product.

calcium ions + sodium carbonate → calcium carbonate + sodium ions

$Ca^{+2} + Na _2CO _3\rightarrow CaCO _3 + 2Na^+$

The water is softened because it no longer contains dissolved calcium ions and magnesium ions, hence we can say that it is converted in soft water. It will now form lather  easily with soap.

Hardness of water is due to soluble salts such as bicarbonates, sulfates an chlorides of magnesium and calcium.

Calcium and Magnesium salts like sulphates, chlorides and bicarbonates cause hardness of water.

Hard water is unfit for laundries because it can not form lather with soap, hence consumption of soap increases and it leaves dirty strains of calcium and magnesium. 

Molar mass of $D _2O$ = $20g$

Water is liquid at room temperature, the most important reason for this is the cohesive forces due to hydrogen bonds in water.

The salt is all dissolved in the water, this makes all of the water much denser than normal water, making it uncomfortable to swim in. Furthermore it means that the water is denser than the human body which is 70%, unsalted water. Meaning it is impossible to sink in the Dead Sea.

$1$ mole of $CaCl _2\equiv1$ mole of $CaCO _3\equiv1$ mole of $MgCl _2$

Milli equivalent of $Ca(HCO _{3}) _{2}$= miili equivalent of $CaCO _{3}$= mili equivalent of $HCl$

The water has maximum density at 4 deg C. When liquid water is converted to ice, an open cage three dimensional structure is formed. Almost half the space is unoccupied. In liquid state, molecules are more closely packed.

Hard water is  percolated over Calgon (sodium hexameta phosphate $Na _6P _6O _{18}$). Calgon reacts calcium ( or magnesium) ions present in hard water. Inactive complex ions are formed that do not precipitate with soap.

In an ion exchange using hard water is not a disadvantage since it becomes soft by exchanging anions or cations. $Na^+$, $Ca^{2+}$ and $Mg^{2+}$ ions (from water) are exchanged with $H^+$ ions (from cation exchange resins). $Cl^-$, $SO _4^{2-}$ and $NO _3^{-}$ ions (from water) are exchanged with $OH^-$ ions (from anion exchange resins).

 Polyphosphates like sodium hexametaphosphate (calgon) form souble complex with cations like $Ca^{2+}$ and  $Mg^{2+}  $present in hard water and hence are used as water softening agents.
$Na _{6}P _{6}O _{18} \rightarrow 2Na^{+}+ Na _{4}P _{6}O^{2-} _{18}$
$M^{2+} + Na _{4}P _{6}O^{2-} _{18}\rightarrow [Na _{2}MP _{6}O _{18}]^{2-} + 2Na^{+}$

Sodium hexametaphosphate $ (Na _6P _6O _{18}),$ commercially called 'calgon' is used for water softening. Calgon reacts with salts of $Ca/Mg$ (present in hard water) and forms inactive complex anions that do not precipitate in soap solution.

The temporary hardness of water is due to the presence of calcium or magnesium bicarbonates. 

Water free from cations $(Ca^{2+}, Mg^{2+}, etc.)$ and anions $(Cl^{-}, SO^{2-} _{4}, HCO^{-} _{3}, etc)  $ is called deionised or demineralised water.

Answer:-

Presence of calcium and magnesium salts in the form of hydrogencarbonate, chloride and sulphate in water makes water 'hard'.

Boiling and Clark's method are used for removing temporary hardness. They cannot be used for removing permanent hardness. Permanent hardness can be removed by treatment with $Na _2CO _3$ which takes place as follows:-

Degree of hardness $=\dfrac {6\times 0.001}{0.05} =120$ ppm.

The metal A is calcium. It reacts with cold water to form calcium hydroxide (C) and hydrogen gas (B) which is colourless and odourless.
$Ca+2H _2O \rightarrow Ca(OH) _2 + H _2$

mole of $ Ca(HCO _{3}) _{2} = \dfrac{162\times 10^{-3}mg}{162\,g/mole} = 1\times 10^{-3}\,moles $

$55.5$ mg of $CaCl _2$ in 1 litre of water corresponds to $55.5$ ppm.

The chemical reaction for softening water can be given as:-