Tag: evs

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Questions Related to evs

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

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

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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

  1. $0^oC$
  2. $4^oC$
  3. $40^oC$
  4. $100^oC$
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

Sodium carbonate softens permanent hard water.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
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.
Multiple choice evs experiments with water water and its types hard and soft water what floats - what sinks

Temporary hardness of water can be removed by:

  1. filtration

  2. boiling

  3. decantation

  4. washing soda
Reveal answer Fill a bubble to check yourself
B Correct answer
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.