Tag: evs

Questions Related to evs

Which element has variable covalency?

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

  1. F

  2. H

  3. I

  4. O

Show answer
Correct Option: C

$ RH _{2} $ (ion exchange resin ) can replace $ Ca^{2+} $ in hard water as : 
$ RH _{2}+Ca^{2+}\rightarrow RCa+2H^{+} $.


One litre of hard water after passing through $ RH _{2} $ has pH = 2. Hence, hardness in ppm of $ Ca^{2+} $ is:

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

  1. 200

  2. 100

  3. 50

  4. 125

Show answer
Correct Option: A
Explanation:

According to the given reaction 


$ RH _{2}+Ca^{2+}\rightarrow RCa+2H^{+} $

Each mole $ Ca^{2+} $ ion replaced by 2 moles $ H^{+}$

1 mole $ H^{+} $ replaced $ \Rightarrow \dfrac{1}{2} = 0.5\,mole \,Ca^{2+} $

Given,
$ pH = 2 $

$ H^{+} = 10^{-2} = 0.01 $

0.01 mole $ H^{+} $ replaced $ = 0.01\times 05 = 0.005\,moles\,Ca^{2+} $

Mass $ Ca^{2+}$ replaced $ = 0.005\times 40 = 0.2\,g = 200\,mg $

Concentration or Hardness of $ Ca^{2+} = 200\,mg/L $

$ = 200\,ppm $   

Hence, the correct option is $\text{A}$

In a laboratory, hard water, required for an experiment, is not available. However, the following salts are available in the school laboratory :
1. Sodium sulphate
2. Calcium sulphate
3. Magnesium chloride
4. Sodium chloride
5. Calcium chloride
6. Potassium sulphate
Which of the above salts may be dissolved in water to obtain hard water for the experiment?

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

  1. 1,3 and 5

  2. 1,2 and 5

  3. 1,2,4 and 6

  4. 3 and 5 only

  5. 2,3 and 5

Show answer
Correct Option: E
Explanation:

The following salts may be dissolved in water to obtain hard water for the experiment
2. Calcium sulphate
3. Magnesium chloride
5. Calcium chloride

Both temporary and permanent hardness in water is removed by:

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

  1. boiling

  2. filtration

  3. distillation

  4. decantation

Show answer
Correct Option: C
Explanation:

Both temporary and permanent hardness in water is removed by distillation. Temporary hardness can be removed by boiling and filtration. Permenant hardnesscan be removed by: (1) adding washing soda, (2) permutit method (3) by using ion exchange resins.

Both temporary and permanent hardness is removed on boiling water with :-

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

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

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

  3. $CaCO _{3}$

  4. $CaO$

Show answer
Correct Option: B
Explanation:

Temporary hardness is removed by boiling water with $NaOH$ and $Na _2CO _3$. $Ca(HCO _3 ) _2+2NaOH \rightarrow CaCO _3 \downarrow +Na _2CO _3+2H _2O$ Permanent hardness is removed by boiling water with sodium carbonate. $CaCl _2+Na _2CO _3 \rightarrow CaCO _3 \downarrow + 2 NaCl$

Both temporary and permanent hardness in water is removed by________.
evs experiments with water water and its types hard and soft water what floats - what sinks

  1. boiling

  2. filtration

  3. distillation

  4. decantation

Show answer
Correct Option: C
Explanation:
Both temporary and permanent hardness in water is removed by distillation. Temporary hardness can be removed by boiling and filtration. permanent hydration can be removed by adding washing soda, permutit method and by using ion exchange resins.

Hard water can be used:

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

  1. in boilers

  2. in textile industry

  3. in paper industry

  4. in drinking

Show answer
Correct Option: D

Calgon is an industrial name given to____________.

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

  1. normal sodium phosphate

  2. sodium meta-aluminate

  3. sodium hexametaphosphate

  4. hydrated sodium aluminium silicate

Show answer
Correct Option: C
Explanation:

Calgon is an industrial name given to sodium hexametaphosphate. Its formula is $Na _{2}[Na _{4}(PO _{3}) _{6}]$.

Temporary hardness of water can be removed by :

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

  1. boiling

  2. saponification

  3. clark's method

  4. chlorination

Show answer
Correct Option: A,C
Explanation:

The temporary hardness of water can be removed by boiling. $Ca(HCO _3) _2 \xrightarrow {boil} CaCO _3 \downarrow + CO _2 \uparrow + H _2O$.

Clark's method which uses lime (calcium hydroxide), it is also used for removal of temporary hardness of water.
$Ca(HCO _3) _2+Ca(OH) _2 \rightarrow 2CaCO _3+2H _2O$.

The exhausted permutit is regenerated by treating sodium hydroxide solution in Clark's method for removing permanent hardness.

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

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

Yes the exhausted permutit is regenerated by treating sodium hydroxide solution in Clark's method for removing permanent hardness.