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

Temporary hardness can be removed by:

  1. boiling

  2. clark's process

  3. calgon's process

  4. permutit method
Reveal answer Fill a bubble to check yourself
A,B Correct answer
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.

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

Permanent hardness of water can be removed by:

  1. permutit process

  2. boiling

  3. ion-exchange

  4. calgon's process
Reveal answer Fill a bubble to check yourself
A,C,D Correct answer
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.

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

Hard water causes _________ .

  1. burning of skin

  2. scales on the boiler walls

  3. relief to the body

  4. head-ache
Reveal answer Fill a bubble to check yourself
A,B Correct answer
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.

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

Salts of calcium and magnesium like ___________ cause harness of water.

  1. bicarbonates

  2. chlorides

  3. sulphates

  4. phosphates
Reveal answer Fill a bubble to check yourself
A,B,C Correct answer
Explanation
Hard water is the water that contains soluble salts of bivalent ions like calcium and magnesium principally in the form of bicarbonates, chlorides, and sulfates. Water is softened on a small scale by the addition of phosphates, together with sodium carbonate (washing soda) which separates the calcium and magnesium as white precipitates of their respective phosphates.
Therefore option $A,\ B,\ C$ are correct
Multiple choice evs experiments with water water and its types hard and soft water what floats - what sinks

If 10 g of a sample of water contains 16.2 g of  $ Ca(HCO _{3}) _{2} $, then the hardness of water is:

  1. 200 ppm

  2. 300 ppm

  3. 60 ppm

  4. 100 ppm
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

If density of water $=1\text{ }g/ml$

$\therefore 10\text{ }ml$ water contains $16.2\text{ }mg$ $Ca(HCO _3) _2$.
$\therefore 1L$ water contains $16.2\times 10^2\text{ }mg$ $Ca(HCO _3) _2$.
Equivalent of $CaCO _3=16.2\times 10^2\times \cfrac{100}{162}=100$
$\therefore $ Hardness in $ppm=100ppm$

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

The hardness of water due to $ HCO^{2-} _{3} $ is 122pm. Select the correct statement(s).

  1. The hardness of water in terms of $ CaCO _{3} $ is 200 ppm
  2. The hardness of water in terms of $ CaCO _{3} $ is 100 ppm
  3. The hardness of water in terms of $ CaCO _{3} $ is 222 ppm
  4. The hardness of water in terms of $ CaCO _{3} $ is 95 ppm
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The hardness of water due to ${ HCO } _{ 3 }^{ 21 }$ is $122ppm$. Because the hardness of water in terms of ${ CaCO } _{ 3 }$ is $200$ $ppm$.

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

Temporary hardness maybe be removed from water by adding?

  1. $Ca(OH{ ) } _{ 2 }$
  2. $CaC{O } _{ 3 }$
  3. $CaS{O } _{ 4 }$
  4. $HCl$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

  • Temporary hardness is caused by dissolved calcium or magnesium hydrogencarbonate.

Some of the methods to remove hardness from water are:

  • Chemical Process of Boiling Hard Water
  • Adding Slaked Lime (Clark's Process)
  • Adding Washing Soda
  • Calgon Process
  • Ion Exchange Process
  • Using Ion Exchange Resins

Clark’s method: In this method calculated amount of lime is added to hard water. It precipitates out calcium carbonate and magnesium hydroxide which can be filtered off.
$Ca(HCO _3) _2+Ca(OH) _2 \rightarrow 2CaCO _3(\downarrow)+2H _2O$
$Mg(HCO _3) _2+Ca(OH) _2 \rightarrow 2CaCO _3(\downarrow)+Mg(OH) _2(\downarrow)+2H _2O$

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

Permanent hardness in water is due to the presence of:

  1. $Ca^{2+},\:Mg^{2+}$
  2. $CaCl _{2},\:MgCl _{2}$
  3. $CaCO _{3},\:MgCO _{3}$

  4. all of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Permanent hardness is caused by the presence of dissolved chlorides and sulfates of calcium and magnesium. Calcium and magnesium ions themselves (Option A) are the cause of both temporary and permanent hardness, but the specific chemical compounds responsible for permanent hardness are the salts like CaCl2 and MgCl2.

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

The reagent commonly used to determine hardness of water is:

  1. oxalic acid

  2. disodium salt of EDTA

  3. sodium citrate

  4. sodium thiosulphate
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Determination of hardness of water:

Determination of hardness of water is done by titration method using the technique of complexometric titration.    

Ethylenediamine tetra-acetic acid and its sodium salts (EDTA) form a chelated soluble complex when it is titrated against a solution containing certain metal cations that cause hardness to water.

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

Which of the following ions present as impurity cannot be removed by calgon process ?

  1. $Ca^{2+}$
  2. $Mg^{2+}$
  3. $Na^+$

  4. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The Calgon process uses sodium hexametaphosphate (NaPO3)6 to sequester calcium and magnesium ions by forming soluble complexes. It does not remove sodium ions, as they are not responsible for water hardness and are often added by the process itself.