Tag: evs

Quizzes (439) Questions (4580)

Questions Related to evs

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

Hardness of water can be removed by :

  1. adding calcium hydroxide

  2. ion-exchange method

  3. both a and b

  4. none of above
Reveal answer Fill a bubble to check yourself
C Correct answer
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.
$Ca+2 + Na2-zeolite Ca-zeolite + 2Na+1$
$Mg+2 +Na2-zeolite Mg-zeolite + 2Na+1$

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

Temporal hardness can be removed by just boiling the water because :

  1. Form salts

  2. Converts magnesium to soluble magnesium

  3. Converts carbonate to soluble carbonate

  4. Converts carbonate to insoluble carbonate
Reveal answer Fill a bubble to check yourself
D Correct answer
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). 

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

Calgon used as water softner is:

  1. $Na _2[Na _4(PO _3) _6]$
  2. $Na _4[Na _2(PO _3) _6] $
  3. $Na _2[Na _4(PO _4) _5]$

  4. none of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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 :

${ Na } _{ 6 }{ P } _{ 6 }{ O } _{ 18 }\rightarrow { 2Na }^{ + }+{ Na } _{ 4 }{ P } _{ 6 }{ O } _{ 18 }^{ 2- }$
${ Ca }^{ 2+ }+{ Na } _{ 4 }{ P } _{ 6 }{ O } _{ 18 }^{ 2- }\rightarrow { \left[ { Na } _{ 2 }{ Ca }{ P } _{ 6 }{ O } _{ 18 } \right]  }^{ 2- }+{ 2Na }^{ + }$

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

In permanent hardness of water, when washing soda is treated with water, ________ is precipitated out.

  1. sodium carbonate

  2. magnesium carbonate

  3. calcium carbonate
  4. $Na _2CO _3 and\ MgCO _3$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

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.