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Questions Related to evs

Calcium and Magnesium salts like _______ cause hardness 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:

Calcium and Magnesium salts like sulphates, chlorides and bicarbonates cause hardness of water.

Hard water is unfit for laundries because:

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

  1. consumes much soap

  2. leaves dirty strains of '$Ca$' and '$Mg$'

  3. causes irritation on skin

  4. water is very hard to handle

Show answer
Correct Option: A,B
Explanation:

Hard water is unfit for laundries because it can not form lather with soap, hence consumption of soap increases and it leaves dirty strains of calcium and magnesium. 

What is the mass of a mole of water containing 50% of heavy water $(D _2O)$?

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

  1. 18 g

  2. 19 g

  3. 20 g

  4. 21 g

Show answer
Correct Option: B
Explanation:

Molar mass of $D _2O$ = $20g$

Molar mass of $H _2O$ = $18g$

If both are present in same ratio (i.e. 50:50) then,

Mass of a mole of water= $\cfrac {20+18}{2}$
=$19g$

 What happens on adding salt to the water in which eggs are boiled?  

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

  1. Egg will take more time to cook

  2. Egg will start floating on water

  3. Egg will cook faster

  4. Egg will sink in water

Show answer
Correct Option: C

Water is liquid at room temperature, the most important reason for this is the :

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

  1. high boiling point of water

  2. high melting point of water

  3. high heat of vapourization of water

  4. cohesive forces due to hydrogen bonds in water

Show answer
Correct Option: D
Explanation:

Water is liquid at room temperature, the most important reason for this is the cohesive forces due to hydrogen bonds in water.

Which of the following is true?

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

  1. Vegetable oil is heavier than water

  2. Ghee is soluble in water

  3. Curd is soluble in water

  4. A person who can not swim will not drown in dead sea

Show answer
Correct Option: D
Explanation:

The salt is all dissolved in the water, this makes all of the water much denser than normal water, making it uncomfortable to swim in. Furthermore it means that the water is denser than the human body which is 70%, unsalted water. Meaning it is impossible to sink in the Dead Sea.

One litre of a samle of hard water contains 1 mg of $CaCl _2$ and 1 mg of $MgCl _2$.Then the total hardness in terms of parts of $CaCO _3$ per $10^8$ parts of water by mass is:

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

  1. 1.954 ppm

  2. 1.260

  3. 0.946

  4. none of these

Show answer
Correct Option: A
Explanation:

$1$ mole of $CaCl _2\equiv1$ mole of $CaCO _3\equiv1$ mole of $MgCl _2$

$\therefore$ $100mg$ $CaCO _3$ is produced by $95mg$ $MgCl _2$
$\therefore$ $1mg$ of $MgCl _2$ gives $\cfrac {100}{95}mg$  $CaCO _3=$ $1.05mg$ $CaCO _3$

Similarly, $1mg$ of $CaCl _2$ gives $\cfrac {100}{111}mg$ $CaCO _3=$ $0.90mg$ $CaCO _3$

$\therefore$ Total $CaCO _3$ per litre of water= $1.05+0.90=1.95$ $mg$
Weight of $1000ml$ of water= $10^3g$=$10^6mg$

$\therefore$ Total hardness in terms of parts of $CaCO _3$ per $10^6$ parts of water by weight = $\cfrac {1.95}{10^6}\times 10^6$
=$1.95$ $ppm$

Answer: (A) $1.954$ $ppm$

100 ml of tap water containing $Ca(HCO _3) _2$ was titrated with N/50 $HCl$ with methyl orange as indicator. If 30ml of $HCl$ were required, calculate the temporary hardness as part of $CaCO _3$ per $10^6$ parts of water.

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

  1. 150 ppm

  2. 300 ppm

  3. 450 ppm

  4. 600 ppm

Show answer
Correct Option: B
Explanation:

Milli equivalent of $Ca(HCO _{3}) _{2}$= miili equivalent of $CaCO _{3}$= mili equivalent of $HCl$

$N _{1}V _{1}= N _{2}V _{2}$
$1000 \times w$/($100$/$2$)= $30$/$50$
$w$= $0.03$ g
For $100$ml the amount of $CaCO _{3} = 0.03$ g
For $10^{6}$ = $0.03 \times 10^{6}$/$100=300$ ppm

The density of water is less in its solid state because:

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

  1. in solid state(ice) , water molecules are arranged in highly ordered open cage like structure

  2. more extensive hydrogen bonding is present in solid state ice

  3. the water molecules are closet in solid state of water

  4. water is a rigid crystalline, closely packed structure in its solid state.

Show answer
Correct Option: A
Explanation:

The water has maximum density at 4 deg C. When liquid water is converted to ice, an open cage three dimensional structure is formed. Almost half the space is unoccupied. In liquid state, molecules are more closely packed.

The formula of calgon is:

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

  1. $Na _{2}\left [ Na _{4}\left ( PO _{3} \right ) _{6} \right ]$

  2. $Na _{4}\left [ Na _{2}\left ( PO _{3} \right ) _{6} \right ]$

  3. $Na _{4}\left [ Na _{2}\left ( PO _{3} \right ) _{3} \right ]$

  4. $Na _{2}\left [ Na _{4}\left ( PO _{3} \right ) _{4} \right ]$

Show answer
Correct Option: A
Explanation:
The formula of calgon is $Na _2[Na _4(PO _3) _6]$. Calgon is a trade name of a complex salt, sodium hexametaphosphate $(NaPO _3) _6$. It is used for softening hard water. 
Calgon ionizes to give a complex anion.