KSEEB Solutions for Class 8 Science Chapter 13 Water

Students can Download Science Chapter 13 Water Questions and Answers, Notes Pdf, KSEEB Solutions for Class 8 Science helps you to revise the complete Karnataka State Board Syllabus and to clear all their doubts, score well in final exams.

Karnataka State Syllabus Class 8 Science Chapter 13 Water

KSEEB Class 8 Science Water Textbook Exercise Questions and Answers

I. Four alternatives are given to each of the following incomplete statements/questions. Choose the right answer.

Question 1.
Magnesium sulphate crystals are commonly called ___________.
(a) Gypsum salt
(b) Epsom salt
(c) green vitriol
(d) Alum
Answer:
(b) Epsom salt

Question 2.
When you buy washing soda from the market, you will get it in powder form because of ___________.
(a ) The crystals of washing soda quickly lose water molecules
(b) The shop keeper prefers to a powder the. crystal.
(c) Washing soda does not form crystals.
(d) Washing soda is a drying agent.
Answer:
(a ) The crystals of washing soda quickly lose water molecules

Question 3.
A sample of hard water is heated in an utensil. A white deposit of calcium carbonate is formed. This is due to the presence of ___________.
(a) Calcium Chloride
(b) Magnesium sulphate
(c) Calcium bicarbonate
(d) Calcium hydroxide
Answer:
(c) Calcium bicarbonate

Question 4.
The salt that cause hardness in water and that liberates carbon dioxide on heating is
(a) Magnesium bicarbonate
(b) Calcium chloride
(c) Magnesium sulphate
(d) Calcium sulphate
Answer:
(a) Magnesium bicarbonate

Question 5.
When steam is passed over red hot iron we get the following products ___________.
(a) Ferric hydroxide and hydrogen
(b) Ferric oxide and hydrogen
(c) Ferrous hydroxide and hydrogen
(d) Ferrous oxide and hydrogen
Answer:
(d) Ferrous oxide and hydrogen

II. Fill the blanks with suitable words:

1. The chemical name of Epsom salt is ___________.
2. The chemical used to soften hard water is ___________.
Answer:
1. Magnesium sulphate,
2. Sodium carbonate

III. Match the following:
A – B
1) Causes scale a) Calcium oxide
2) Basic oxide b) Soap
3) Test for hardness c) Sulphur dioxide of water
4) Acidic oxide d) Calcium bicarbonate, e) Neutral oxide, f) Does not react with water
Answer:
1. d,
2. a,
3. b,
4. c

IV. Answer the following :

Question 1.
Water is tasteless, but we experience different tastes of water in different places. Why?
Answer:
Water obtained from different places has several salts dissolved in it, therefore water has different taste even though pure water is tasteless.

Question 2.
Write the balanced equations for the reaction of sodium, potassium and calcium on cold water.
Answer:
a) 2 Na + 2 H₂O → 2 Na OH + H₂↑
b) 2 K + 2 H₂O → 2 KOH + H₂ ↑
c) Ca + 2 H₂O → Ca (OH)₂ + H₂ ↑

Question 3.
What happens when steam is passed over red hot iron? Write the equation.
Answer:
When steam is passed over a red hot iron, hydrogen is liberated along with the formation of ferric oxide.
3 Fe + 4 H₂O → Fe₃ O₄ + 4 H₂

Question 4.
Define the terms efflorescence and Deliquescence.
Answer:
Loss of water from hydrated compounds to the surroundings is called efflorescence. Certain water-soluble substances: when exposed to the atmosphere at ordinary temperature, absorb moisture from the atmospheric air to become moist and dissolve in the absorbed water. This phenomenon is called deliquescence.

Question 5.
Give two reasons to prove that water is a compound and not an element.
Answer:
Though water contains combustible hydrogen and oxygen a supporter of combustion it is neither a supporter of combustion nor a combustible substance. Water has a different property which hydrogen and oxygen do not have i.e. it is a very good fire extinguisher. The compound does not show the properties of elements by which “it is formed but it will have a different property since it is a new substance. By this one can prove that water is a compound.

Question 6.
Name three metals which do not react with water under normal conditions.
Answer:
Copper, aluminium, and tin are three such metals which do not react with water under normal conditions.

Question 7.
Name the products formed when the following oxides are dissolved in water. Write balanced equations.
Answer:
(a) Sulphur dioxide: When sulphur dioxide is dissolved in water, sulphurous acid is formed.

SO₂ + H₂O → H₂ SO₃

(b) Carbon dioxide: When carbon dioxide dissolves in water carbonic acid is formed.

CO₂ + H₂O → H₂ CO₃

KO + H₂O → KOH

(d) Calcium oxide: When calcium oxide is dissolved in water Calcium hydroxide is formed.

Ca O + H₂O → Ca (OH)₂

Question 8.
State the reasons for hardness in water.
Answer:
Presence of water-soluble calcium and magnesium bicarbonates, sulphates, and chlorides cause hardness in water.

V. Give reasons for the following:

Question 1.
Sodium metal should be stored under kerosene.
Answer:
Sodium metal should be stored under kerosene as it can react with oxygen and water vapours present in air and kerosene has no affinity towards sodium.

Question 2.
Washing soda loses its crystal structure quickly.
Answer:
Washing soda loses its crystal structure quickly as it loses water when exposed to air of moderate humidity. It is an efflorescent substance.

Question 3.
When calcium nitrate crystals are exposed to air, a solution is formed?
Answer:
Calcium nitrate, when exposed to air, absorbs moisture from the atmospheric air to become moist and dissolve in the absorbed water therefore it cannot be in the crystal form. It is a deliquescent substance.

KSEEB Class 8 Science Water Additional Questions and Answers

Question 1.
What is meant by Hydrotherapy?
Answer:
The Ayurveda water has been given an important place and it is used to treat common health problems. This is called Hydrotherapy.

Question 2.
Mention the steps in the water treatment.
Answer:
Water treatments include stages of coagulation or sedimentation, filtration, decolouration, deodorization, and sterilization.

Question 3.
Water is called the universal solvent. Why?
Answer:
Water is called the universal solvent because it dissolves more substances than any other solvent.

Question 4.
Many metals and their alloys are used to prepare utensils. Why?
Answer:
Many metals and their alloys are used to prepare utensils because they do not react with water under normal conditions.

Question 5.
What happens when sodium is dropped in water?
Answer:
Sodium reacts with water violently. The sodium piece moves around water gradually diminishes in size and finally disappears. It dissolves in water forming sodium hydroxide and hydrogen.

Question 6.
What is rust? How can this be prevented?
Answer:
Rust is a hydrated oxide of Iron. This can be prevented by galvanizing, painting, electroplating with chromium, alloying, etc.

Question 7.
Rusting is quick in the rainy season. Why?
Answer:
The two favourable conditions needed for rusting are oxygen and moisture. The humidity will be more in the rainy season, which promotes rusting.

Question 8.
What is water gas? Mention its uses.
Answer:
The mixture of carbon monoxide and hydrogen in the ratio of 1 : 2 is called water gas. The uses of water gas are:

as an industrial fuel
used in the manufacture of hydrogen

Question 9.
What happens when steam is passed over red hot coke and silicon.?
Answer:
When steam is passed over red hot coke a mixture of carbon monoxide and hydrogen is formed.

C + H₂O → CO ↑ + H₂↑

When steam is passed over red hot silicon, silicon dioxide and hydrogen gas are formed.

Si + 2 H₂O → Si O₂ ↑ + H₂↑

Question 10.
Give some examples of the substances which can absorb moisture.
Answer:
The substances which absorb moisture are magnesium chloride, solid sodium hydroxide, solid potassium hydroxide, anhydrous calcium chloride, calcium nitrate, ferric chloride, and sodium nitrate.

Question 11.
Give two examples of desiccants.
Answer:
Concentrated sulphuric acid and calcium chloride monohydr&te are examples for desiccants.

Question 12.
Give examples of efflorescent substances.
Answer:
Sodium sulphate (Na₂ SO₄ 10 H₂O) and washing powder
(Na₂ CO₃ H₂O) are examples of efflorescent substances.

Question 13.
Calcium Carbonate does not cause hardness. Why?
Answer:
Calcium Carbonate does not cause hardness because it is insoluble in water.

Question 14.
What is meant by soft water?
Answer:
The water which gives lather readily with soap is called soft water.

Question 15.
What is meant by hard water?
Answer:
The water which does not give lather with soap is called hard water.

Question 16.
Why is hard water not used in industrial boilers?
Answer:
Hard water contains calcium and magnesium soluble salts. If it is used in industrial boilers, it forms insoluble salts pf Calcium and magnesium. They produce scales on the inner walls of the boilers, which reduces heating efficiency. There are chances of the explosion of boilers due to foaming. It also corrodes the boilers.

Question 17.
What is meant by Desalinisation?
Answer:
Desalinisation is an artificial process by which saline water (generally sea water) is converted into freshwater.

II. Fill in the blanks:

Question:

The human body has about __________ % of water.
In the water treatment for sedimentation __________ is used.
The acid present in soft drinks is __________.
The by product got during desalinisation is __________.
The formula for Epsom salt is __________.

Answers:

65%,
Alum,
Carbonic acid,
Sodium chloride,
MgSO₄

III. Choose the correct answer from the alternatives given.

Question 1.
The soft metals along the following are
(a) Sodium and aluminium
(b) Sodium and Potassium
(c) Potassium and aluminium
(d) Aluminium and gold
Answer:
(b) Sodium and Potassium

Question 2.
The process by which hydrogen is manufactured is
(a) BOSCH process
(b) Frasch process
(c) Bessemer process
(d) Froth process
Answer:
(a) BOSCH process

Question 3.
The chemical which does not become wet, among the following is
(a) Calcium nitrate
(b) Sodium nitrate
(c) Potassium nitrate
(d) Magnesium chloride
Answer:
(c) Potassium nitrate

Question 4.
The hardness of water is due to the presence of the salts of
(a) Na and Ga
(b) Ca and K
(c) Na and K
(d) Ca and Mg
Answer:
(d) Ca and Mg

Question 5.
The gas liberated when temporary hard water is boiled is
(a) CO₂
(b) CO
(c) Cl
(d) SO₂
Answer:
(a) CO₂

Question 6.
During the boiling of temporary hard water, a white crust is formed inside the vessel, this is due to the deposition of
(a) Calcium and magnesium chloride
(b) Calcium and Magnesium Carbonates
(c) Calcium and magnesium bicarbonates
(d) Calcium and magnesium sulphates
Answer:
(b) Calcium and Magnesium Carbonates

Question 7.
While washing clothes using soap, the lather is not produced, then salt present in the water is of
(a) Calcium
(b) Sodium
(c) Potassium
(d) aluminium
Answer:
(a) Calcium

Question 8.
Water-gas is a mixture of
(a) CO₂ and H₂
(b) H₂ and O₂
(c) CO and O₂
(d) CO and H₂
Answer:
(d) CO and H2

IV. Match the following:

A – B
1) Washing Soda – a) Ca O
2) Baking Soda – b) Na₂ CO₃
3) Quick lime – c) KOH
4) Slaked limed – d) Ca CO₃
5) Epsom Salt – e) Na₂ CO₃, H₂O
6) Limestone – f) K₂SO₄, Al₂ (SO₄)₃ 24H₂O
7) Caustic Soda – g) Ca (OH)₂
8) Lime water – h) Na H CO₃
9) Alum – i) Mg SO₄
10) Soda ash – J) Na OH
Answer:
1. e,
2. h,
3. a,
4. c,
5. I,
6. d,
7. j,
8 g,
9. f,
10. b.

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