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Questions Related to evs

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

Show answer
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

Show answer
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.

Calgon used as water softner is:

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

  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

Show answer
Correct Option: A
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 :

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

Water which doesn't give lather immediately with soap is called soft water.

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:

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

At ________ $^0C$ water has its maximum density and its minimum volume.

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

  1. $40$

  2. $4$

  3. $14$

  4. $24$

Show answer
Correct Option: B
Explanation:

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 ________ and ________.

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

  1. calcium and magnesium

  2. calcium and sodium

  3. sodium and magnesium

  4. calcium and potassium

Show answer
Correct Option: A
Explanation:

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

We can cook pulses easily in hard water. 

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:

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

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

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

  1. sodium carbonate

  2. magnesium carbonate 

  3. calcium carbonate

  4. $Na _2CO _3  and\ MgCO _3$

Show answer
Correct Option: C
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.

Hardness of water is due to soluble salts:

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

  1. Bicarbonates

  2. Sulphates

  3. Chlorides

  4. All of these

Show answer
Correct Option: D
Explanation:

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