Selina Concise Class 8 Chemistry Chapter 8 Water Solution

Selina Concise Class 8 Chemistry Solution Chapter No. 8- ‘Water’ For ICSE Board Students.

1)

Answer : i.) Oceans, ii)  Seas , iii) rivers , iv) lakes , v) Ponds etc.

2)

Answer: The importance of water in nature is following.

  • Water cycle make or enable the availability of water for all living things or organisms.
  • Water cycle is monitored or control the whether on the earth.
  • Water cycle help the balance water in environment in various form or state.
  • Interchange of state from one form to another form water through water cycle.

3)

Answer: Water is very precious for all living things because water is source of life and only 1% water can be usable on earth for most of the  living beings , and  living organisms can not survive without water , all the things we grow in a field due the water , without water we can’t grow a vegetable , cereals , pulses etc .that’s why water is most Precious for living beings.

4)

Answer :

  • Hydrogen and oxygen two gases which is formed water .
  • Chemical composition of water are hydrogen (H2) and oxygen (O2) which present in the water by mass 1:8 ratio. And by volume 2:1 ratio.
  • Molecular formula of water is H2O.

5)

a)

Answer : If the pressure is increased boiling point of water is increased.

b)

Answer: If the impurities present in water freezing point of water is low or decreased boiling point of water is high or increased. For example if we added salt or sugar in water, vapour pressure is decrease or low and boiling point of water is increased or high.

6)

a)

Answer: Water is used as a cooling agent because water has high specific heat properties, water is a neutral it is neither heat up fast or not cool down quickly this nature make water excellent cooling agent.

b)

Answer: Water pipe burst in server winter because during winter water inside the pipe turn into a ice and volume of ice increase and it is expand due to this Expansion it is created pressure inside the pipe so it is burst.

c)

Answer : It is difficult to cook in hills as compared to plains because on the hills atmospheric pressure and boiling temperature is lower as compared to plains , so it take more time to cooked food on hills.

d)

Answer: Ice float on water because  ice has low density as compared to water that is why ice float on water.

e)

Answer: Sea water does not freeze at 0°C because sea water contains salt, and other impurities in it, if the impurities present in water, freezing point of water is low or decreased . Due to this sea water does not freeze 0°C. It is freeze below 0°C.

7)

Answer : Anomalous expansion of water help the aquatic Organism help in cold climate, during winter water is cold and it become dense, its sink, it happened when temperature reach 4°C after this temperature reach 0°C and water become ice (solid)and form a layer of ice on the surface of water (rivers , lakes ,ponds) . temperature under this ice layer not change . This ice layer present water surface protect inside water from cold air, this anomalous expansion of water preserve aquatic animal life during cold whether or climate.

Exercise – 2 Solution

1)

a)

Answer : Solution :

A uniform homogeneous mixture of one or more components ( solid , liquid, gas)  uniformly distributed ina solvent called solution.

b)

Answer : Solvent :

A one state of component or substance that can dissolved another components in it , which formed solution is called solvent.

c)

Answer :  Solute :

A substance that dissolved in a solvent and formed a homogeneous mixture of solution are called solute.

2)

a)

Answer : Unsaturated Solution:

A solution where solute can be dissolved more or the solution can be capable to dissolve more solute and concentration of solute low this type of  solution is called unsaturated solution.

b)

Answer: Saturated Solution:

A solution that dissolved more solute until they are unable to dissolve solute anymore, undissolved components of solute  settle at the bottom this type of solution are known as saturated Solution.

c)

Answer : Supersaturated solution :

A solution is can be dissolved excess or maximum solute , after cool down when given the  heat or temperature to saturated solution, this type of solution is known as supersaturated solution.

3)

a)

Answer : A solubility of a solid (solute) get affected by increase in temperature that is when the temperature is increased solubility of solid ( solute ) increase . And When the temperature increased solubility of gas (solute) decreased .

b)

Answer : When increased the pressure solubility of solid ( solute) not affected their solubility neither increase  nor decreased, But when the pressure increases solubility of gas (solute) increased.

4)

a)

Answer :

Sr.No. Solution Suspension
1 Solution is a homogeneous mixture Suspension is a heterogeneous mixture
2 Particles size are less than 1nm. Particles size are 10-7 m.
3 Solution is transparent in nature due to this there is no scattering of light. Suspension is a opaque in nature due to this there is scattering and reflection of light occurred.
4 Particles are uniformly dispersed in solution. Particlesare not uniformly dispersed in suspension
5 Example : NaCl in water , and sugar in water etc. Example : Sand in water , chalk in water , mud in water etc.

 b)

Answer :

Sr.No. Suspension Colloid
1 Suspension is a heterogeneous mixture Colloid are also a heterogeneous mixture.
2 Suspension Particles  size are 10-7 m. Colloidal Particles  size are in between10-10m to 10-7m.
3 Particles can not see by necked eye. Particles can seen by necked aye.
4 Suspension particles undergo in sedimentation. Colloidal particles do not undergo in n sedimentation.
5 Suspension particles can not pass through filter paper Colloidal particles can be pass through filter paper
6 Example : sand in water, mud in water , chalk in water etc. Example : Milk , blood , ink , etc.

5)

a)

Answer :  Water of Crystallization :

The definite number of water molecules chemically combine with a substance atom or molecules crystal or one formula unit of crystal components are known as water of crystallization .

Example : i) Sodium carbonate decahydrate ( washing soda)

Formula : Na₂CO₃.10H₂O

ii) Magnesium Sulphate heptahydrate ( Epsom salt)

Formula : MgSO₄.7H₂O

6)

a)

Answer : Hydrated substance :

  • Sodium carbonate decahydrat ( washing soda) Na₂CO₃.10H₂O
  • Magnesium sulphate heptahydrate ( Epsom salt) MgSO₄.7H₂O

 b)

Answer : crystalline anhydrous substance:

  • Sodium chloride ( Common Salt ) NaCl
  • Sugar C₁₂ H₂₂ O₁₁

c)

Answer : Drying agent :

  • Phosphorous pentoxide P₂ O₅
  • Calcium oxide ( quicklime) Cao
  • Silica Gel

d)

Answer : Deliquescent  substance  :

  • Sodium hydroxide ( caustic soda) NaOH
  • Magnesium chloride MgCl₂
  • Calcium chloride CaCl₂

e)

Answer : Efflorescent substance :

  • Sodium sulphate decahydrat (Glauber’s Sal) Na₂SO₄.10H₂O
  • Sodium carbonate decahydrat ( washing soda) Na₂CO₃.10H₂O

f)

Answer : Colloids :

  • Milk , Blood
  • Ink , bellies

g)

Answer : Solvent other than water :

  • Acetone
  • Ethanol
  • Turpentive

7)

a)

Answer :

When Blue vitriol heated in a test tube, colourless liquid removed from the. Copper sulphate pentahydrate. This  Colourless liquid is water, due to this blue colour copper sulphate pentahydrate convert into White powder (amorphous) , if we again bring back the colourless liquid ( water ) into a copper sulphate pentahydrate ( white powder)  it will again back to blue in colour.

b)

Answer : Sodium carbonate decahydrat ( washing soda)  Na₂CO₃.10H₂O is the Efflorescence substance , when it exposed to air it change from crystalline to white powder ( amorphous)

c)

Answer :Water is a neutral liquid when blue litmus paper added or deep in water it has no change because the neutrality of water .

8)

a)

Answer : Silica gel pouches are  kept in unused  water bottle because silica gel removed or absorbed moisture from the other things without chemically reacting with them , and keep the things dry.

b)

Answer : Table salt become moist during rainy season because table salt contain some contamination like Magnesium chloride , Calcium chloride which are deliquescence substance , so during rainy season they absorbed water from atmosphere and become moist .

c)

Answer : On  a bottle of   cold drink, a fizz sound is heard because in cold drinks carbon dioxide gas at under pressure so due to this carbon dioxide gas and pressure we heard fizz sound when we open cold drinks bottle.

9)

a)

Answer :  Sodium

Sodium react with water to produce sodium hydroxide and hydrogen gas very fast.

b)

Answer :  Iron

When iron in hot chemically react with water steam to produce Tri ferric tetaroxide and hydrogen gas.

3Fe   +  4H₂O    ⇋      Fe₃O₄     +   4H₂ (gas)

c)

Answer : Carbon dioxide

When carbon dioxide react with water to produce carbonic acid.

             CO₂    +        H₂O     →  H ₂CO₃

Carbon dioxide        Water.              Carbonic acid

d)

Answer :  Sodium Oxide

When sodium oxide is react with water to produce alkali sodium hydroxide .

    Na₂O     + H₂O    →  2NaOH

Sodium oxide.          Water.        Sodium hydroxide

11)

a)

Answer : Water gas ( CO + H2 )

When steam is passed over hot coke water gas is produced.

b)

Answer :  Oxygen  gas

When chlorine is dissolved to water and exposed to sunlight oxygen gas is produced .

c)

Answer : Hydrogen gas

When a piece of calcium is added to water hydrogen gas is produced.

d)

Answer :    Carbon dioxide

When fossils fuel is burnt carbon dioxide gas is produced.

Updated: July 6, 2021 — 10:49 pm

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