Tag: experiments with water

Questions Related to experiments with water

Calgon used as water softner is:

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

  1. $Na _2[Na _4(PO _3) _6]$

  2. $Na _4[Na _2(PO _3) _6] $

  3. $Na _2[Na _4(PO _4) _5]$

  4. none of the above

Show answer
Correct Option: A
Explanation:

Calgon $\rightarrow { Na } _{ 6 }{ P } _{ 6 }{ O } _{ 18 }\rightarrow { Na } _{ 2 }\left[ { Na } _{ 4 }{ \left( { PO } _{ 3 } \right)  } _{ 6 } \right] $ it is used as water softener, when added to hard water following reaction takes place :

${ Na } _{ 6 }{ P } _{ 6 }{ O } _{ 18 }\rightarrow { 2Na }^{ + }+{ Na } _{ 4 }{ P } _{ 6 }{ O } _{ 18 }^{ 2- }$
${ Ca }^{ 2+ }+{ Na } _{ 4 }{ P } _{ 6 }{ O } _{ 18 }^{ 2- }\rightarrow { \left[ { Na } _{ 2 }{ Ca }{ P } _{ 6 }{ O } _{ 18 } \right]  }^{ 2- }+{ 2Na }^{ + }$

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:

Soft water gives lather with soap immediately whether the hard water does not produce lather with soap.

At ________ $^0C$ water has its maximum density and its minimum volume.

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

  1. $40$

  2. $4$

  3. $14$

  4. $24$

Show answer
Correct Option: B
Explanation:

The density of water is maximum at $4^oC$ and hence its volume at this temperature is minimum.

Hardness of water is mainly due to the dissolved salts of ________ and ________.

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

  1. calcium and magnesium

  2. calcium and sodium

  3. sodium and magnesium

  4. calcium and potassium

Show answer
Correct Option: A
Explanation:

Hardness of water is mainly due to the dissolved salts of calcium and magnesium.

We can cook pulses easily in hard 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:

The dissolved salts in hard water do not let the pulses cook easily.

In permanent hardness of water, when washing soda is treated with water, ________ is precipitated out.

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

  1. sodium carbonate

  2. magnesium carbonate 

  3. calcium carbonate

  4. $Na _2CO _3  and\ MgCO _3$

Show answer
Correct Option: C
Explanation:

The carbonate ions from sodium carbonate react with the calcium and magnesium ions in the water to produce insoluble product.

calcium ions + sodium carbonate → calcium carbonate + sodium ions

$Ca^{+2} + Na _2CO _3\rightarrow CaCO _3 + 2Na^+$

The water is softened because it no longer contains dissolved calcium ions and magnesium ions, hence we can say that it is converted in soft water. It will now form lather  easily with soap.

Hardness of water is due to soluble salts:

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

  1. Bicarbonates

  2. Sulphates

  3. Chlorides

  4. All of these

Show answer
Correct Option: D
Explanation:

Hardness of water is due to soluble salts such as bicarbonates, sulfates an chlorides of magnesium and calcium.

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= $\cfrac {20+18}{2}$
=$19g$