Tag: evs

Questions Related to evs

Calgon removes hardness by forming complex compounds with the $Ca^{2+}$and $Mg^{2+}$ ions of hard water or by adsorption.

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:

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


$Na _2[Na _4(PO _3) _6]+2CaSO _4\longrightarrow 2Na _2SO _4+Na _2[Ca _2(PO _3) _6]$ soluble

In the same way, $Mg^{2+}$ can also precipitate as $Na _2[Mg _2(PO _3) _6]$ and water becomes free from $Mg^{2+}$ and $Ca^{2+}$ ions.

Thus the answer is True.

The density of water is not same at all temperatures because of its anomalous expansion. The density is maximum at:

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

  1. $0^oC$

  2. $4^oC$

  3. $40^oC$

  4. $100^oC$

Show answer
Correct Option: B
Explanation:

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 for removing permanent hardness.

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:

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

hence, calgon is used for removing permanent hardness.

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

Show answer
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

Show answer
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

Show answer
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

Show answer
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

Show answer
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

Show answer
Correct Option: B
Explanation:

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