Tag: evs

Questions Related to evs

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.

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

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

  1. bicarbonates

  2. chlorides

  3. sulphates

  4. phosphates

Show answer
Correct Option: A,B,C
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

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

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

  1. 200 ppm

  2. 300 ppm

  3. 60 ppm

  4. 100 ppm

Show answer
Correct Option: D
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 $ppm=100ppm$

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

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

  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

Show answer
Correct Option: A
Explanation:

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

Temporary hardness maybe be removed from water by adding?

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

  1. $Ca(OH{ ) } _{ 2 }$

  2. $CaC{O } _{ 3 }$

  3. $CaS{O } _{ 4 }$

  4. $HCl$

Show answer
Correct Option: A
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.
$Ca(HCO _3) _2+Ca(OH) _2 \rightarrow 2CaCO _3(\downarrow)+2H _2O$
$Mg(HCO _3) _2+Ca(OH) _2 \rightarrow 2CaCO _3(\downarrow)+Mg(OH) _2(\downarrow)+2H _2O$

Permanent hardness in water is due to the presence of:

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

  1. $Ca^{2+},:Mg^{2+}$

  2. $CaCl _{2},:MgCl _{2}$

  3. $CaCO _{3},:MgCO _{3}$

  4. all of the above

Show answer
Correct Option: B

The reagent commonly used to determine hardness of water is:

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

  1. oxalic acid

  2. disodium salt of EDTA

  3. sodium citrate

  4. sodium thiosulphate

Show answer
Correct Option: B
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.

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

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

  1. $Ca^{2+}$

  2. $Mg^{2+}$

  3. $Na^+$

  4. None of these

Show answer
Correct Option: C