Tag: what floats - what sinks

Questions Related to what floats - what sinks

Which of the following substance is not present in clear water?

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

  1. $Ca\left ( HCO _{3} \right ) _{2}$

  2. $MgCl _{2}$

  3. $CaSO _{4}$

  4. $CaCO _{3}$

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Correct Option: D
Explanation:

$CaCO _3$ is not present in the clear water. It attains the temporary hardness to the water.

Identify the substance that is not a water softener.

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

  1. $NaOH$

  2. $Na _{2}CO _{3}$

  3. $Na _{2}Al _{2}Si _{2}O _{8}$

  4. $MgCl _{2}$

Show answer
Correct Option: D
Explanation:

The substance that is not a water softener $MgCl _2$, which is responsible for permanent hardness of water.


Other compounds are used for softening of water.

Option D is correct.

............ process is used for the removal of hardness of water.

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

  1. Calgon

  2. Baeyer

  3. Serpeck

  4. Hoope

Show answer
Correct Option: A
Explanation:
Calgon process is used for the removal of hardness of water. 

Calgon is a trade name of a complex salt, sodium hexametaphosphate $(NaPO _3) _6$. 

It is used for softening hard water.

Option A is correct.

Hard water can be softened in ?

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

  1. A chromatograph

  2. An ion exchanger

  3. A calorimeter

  4. An earthenware pot

Show answer
Correct Option: B
Explanation:

Answer:- (B) An ion exchanger

Explanation:-
In ion exchanger, the hard water is softened because it no longer contains calcium or magnesium ions. Ion exchange units that replaces calcium and magnesium ions from water are known as water softeners.

Sodium hexa-metaphosphate is known as:

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

  1. calgon

  2. permutit

  3. natalite

  4. nitrolim

Show answer
Correct Option: A
Explanation:

Sodium hexametaphosphate $(NaPO _3) _6$, is known as calgon.

It is used for softening hard water.

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:
Soaps are basically sodium salt of fatty acids. 

In the presence of excess calcium and magnesium ions in water, the sodium ions are replaced by these ions and are precipitated as scum. 

Water containing an excess of these (calcium and magnesium) ions is called hard water.

Therefore option $B$ is correct.

One litre of a sample of hard water contain $4.44mg$ $Ca{Cl} _{2}$ and $1.9mg$ of $Mg{Cl} _{2}$, what is the total hardness in terms of ppm of $Ca{CO} _{3}$ :

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

  1. $2$ ppm

  2. $3$ ppm

  3. $4$ ppm

  4. $6$ ppm

Show answer
Correct Option: D
Explanation:

$1$ mole $CaCl _2\equiv 1$ mole $CaCO _3\equiv 1$ mole $MgCl _2$

$\therefore 100g$ $CaCO _3$ produces $111g$ of $CaCl _2$
$\therefore 4.44mg$ $CaCl _2$ produces $\cfrac {4.44\times 100}{111}mg$ $CaCO _3$
Similarly, $100g$ $CaCO _3$ is required for $95g$ $MgCl _2$
$\therefore 1.9mg$ $MgCl _2=\cfrac {1.9\times 100}{95}mg$ $CaCO _3$
                               $=2mg$ $CaCO _3$
Total hardness= Hardness due to $CaCl _2$+Hardness due to $MgCl _2$
                         =$4+2$
Total hardness=$6$ $ppm$

Temporary hardness can be removed by:

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

  1. boiling

  2. clark's process

  3. calgon's process

  4. permutit method

Show answer
Correct Option: A,B
Explanation:

By boiling : - On boiling, soluble $Mg{ \left( HC{ O } _{ 3 } \right)  } _{ 2 }$ is converted to insoluble $Mg{ \left( OH \right)  } _{ 2 }$ and $Ca{ \left( H{ CO } _{ 3 } \right)  } _{ 2 }$ to insoluble ${ CaCO } _{ 3 }$. It is because high solubility of $Mg{ \left( OH \right)  } _{ 2 }$ as compared to $Mg{ CO } _{ 3 }$, than $Mg{ \left( OH \right)  } _{ 2 }$ is precipitated. Precipitates can be removed by filtration.


By Clark's Method : Calculated amount of lime is added to hard water $\rightarrow Ca{ CO } _{ 3 }$ precipitates out & $Mg{ \left( OH \right)  } _{ 2 }$ can be filtered off.

Permanent hardness of water can be removed by:

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

  1. permutit process

  2. boiling

  3. ion-exchange

  4. calgon's process

Show answer
Correct Option: A,C,D
Explanation:

Permanent hardness of water can be removed by permutit process. Permutite is an artifical zeolite used for softening of water. Through ion-exchange process, here cation-anion exchange chamber is used to obtain pure water. In calgon's process sodium hexa meta phosphate is used to soften the water.

Hard water causes _________ .

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

  1. burning of skin

  2. scales on the boiler walls

  3. relief to the body

  4. head-ache

Show answer
Correct Option: A,B
Explanation:

Hard water contains minerals specifically $Ca,Mg$ and $Fe$ which can dry our skin and cause flaking and itching.

The presence of these minerals also causes scaling in boiler walls as these minerals are less soluble in hot than cold or to the presence of too high concentration of silica in relation to the alkalinity of water in the boiler.