Tag: hard and soft water

Questions Related to hard and soft water

State whether the given statement is true or false:

In anion exchange resin the anions of hard water get replaced by $OH^-$ ions.

evs experiments with water water and its types hard and soft water what floats - what sinks

  1. True

  2. False

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Correct Option: A
Explanation:

In anoin exchange resin the reaction takes place as

$NH _4^+OH^- + HCl \rightarrow NH _4Cl + H _2O$
so, the anion of hard water get replaced by $OH^-$ ion.

Sodium carbonate softens permanent hard water.

evs experiments with water water and its types hard and soft water what floats - what sinks

  1. True

  2. False

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Correct Option: A
Explanation:
Sodium carbonate, $Na _2CO _3$ is also known as washing soda. It can remove temporary and permanent hardness from water. It is soluble in water and adds a large amount of carbonate ions to the water. These react with dissolved calcium and magnesium ions in the water to produce insoluble precipitates.

Hence, it is a true statement.

Presence of magnesium chloride in water makes it temporary hard.

evs experiments with water water and its types hard and soft water what floats - what sinks

  1. True

  2. False

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Correct Option: B
Explanation:

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

Temporary hardness of water can be removed by:

evs experiments with water water and its types hard and soft water what floats - what sinks

  1. filtration

  2. boiling

  3. decantation

  4. washing soda

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Correct Option: B
Explanation:

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

$Ca{ \left( { HCO } _{ 3 } \right)  } _{ 2 }\left( aq \right) \rightarrow CaC{ O } _{ 3\left( s \right)  }+{ CO } _{ 2\left( g \right)  }+{ H } _{ 2 }O(l)$
$Mg{ \left( HCO \right)  } _{ 3 }(aq)\rightarrow Mg{ CO } _{ 3\left( s \right)  }+{ CO } _{ 2\left( g \right)  }+{ H } _{ 2 }{ O } _{ (l )}$
Then the water obtained will be free from $Ca$ and $Mg$ ions and is soft.

The temporary hardness is caused due to:

evs experiments with water water and its types hard and soft water what floats - what sinks

  1. calcium carbonate only

  2. magnesium bicarbonate only.

  3. calcium bicarbonate only

  4. both magnesium and calcium bicarbonate

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Correct Option: D
Explanation:

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

Calcium bicarbonate in water makes it permanently hard.

evs experiments with water water and its types hard and soft water what floats - what sinks

  1. True

  2. False

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Correct Option: B
Explanation:

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

Permanent hardness of water is due the presence of:

evs experiments with water water and its types hard and soft water what floats - what sinks

  1. calcium carbonate

  2. calcium chloride

  3. calcium bicarbonate

  4. calcium sulphide

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Correct Option: B
Explanation:

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

Hardness of water can be removed by :

evs experiments with water water and its types hard and soft water what floats - what sinks

  1. adding calcium hydroxide

  2. ion-exchange method

  3. both a and b

  4. none of above

Show answer
Correct Option: C
Explanation:

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 hardness can be removed by just boiling the water because :

evs experiments with water water and its types hard and soft water what floats - what sinks

  1. Form salts

  2. Converts magnesium to soluble magnesium

  3. Converts carbonate to soluble carbonate

  4. Converts carbonate to insoluble carbonate

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Correct Option: D
Explanation:

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). 

The reddish brown stains when clothes are washed with hard water is due to :

evs experiments with water water and its types hard and soft water what floats - what sinks

  1. Limestone

  2. Calcium

  3. Ferrous ions

  4. All of the above

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Correct Option: C
Explanation:

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.