ICSE Living Science Chemistry for Class 8 Solutions Chapter 8 Water

Check Your Progress (Page 100)

Answer the following.
Question 1.
What are the main sources of water?
Answer:
Surface water is found in the oceans, seas, rivers, lakes, streams, etc. Sources of groundwater include springs and wells.

Question 2.
Water dissolves all nitrate salts and most chloride salts. True or false?
Answer:
True.

Question 3.
Differentiate between miscible and immiscible liquids.
Answer:
Liquids that dissolve in water are called miscible liquids that do not dissolve in water are called immiscible liquids.

Question 4.
What type of solution is sugar in water – homogeneous or heterogeneous?
Answer:
A solution of sugar in water is a homogeneous mixture.

Question 5.
Can you see the particles of a suspension?
Answer:
The particles of suspensions can be seen with the naked eye.

Check Your Progress (Page 107)

Answer these following.
Question 1.
Calcium chloride is a hygroscopic substance. True or false?
Answer:
True.

Question 2.
What will happen when sodium reacts with cold water?
Answer:
Sodium react with cold water to liberate hydrogen gas and form the corresponding metal hydroxide.
ICSE Class 8 Chemistry Notes Chapter 8 Water - 1

Question 3.
What is the chemical formula of aluminium oxide?
Answer:
The chemical formula of aluminium oxide is Al2O3.

Question 4.
Write the reaction between magnesium oxide and water.
Answer:
ICSE Class 8 Chemistry Notes Chapter 8 Water - 2

Question 5.
What are the types of hardness of water?
Answer:
There are two types of hardness of water :

  • Temporary hardness of water.
  • Permanent hardness of water.

A. Tick the most appropriate answer

Question 1.
Which of the following exists in three different states in natural conditions on the earth?
a. soil
b. water
c. oxygen
d. salt
Answer:
b. water

Question 2.
Which of the following does not dissolve in water?
a. sand
b. sugar
c. salt
d. vinegar
Answer:
a. sand

Question 3.
What type of solution is milk?
a. homogeneous solution
b. suspension
c. colloid
d. none of these
Answer:
c. colloid

Question 4.
Which of the following is an anhydrous salt?
a. copper sulphate pentahydrate
b. calcium chloride hexahydrate
c. Magnesium sulphate heptahydrate
d. sodium nitrate
Answer:
d. sodium nitrate

Question 5.
Which gas is evolved during the reaction of water with metals?
a. carbon dioxide
b. hydrogen
c. oxygen
d. nitrogen
Answer:
b. hydrogen

Question 6.
By which of the following can temporary hardness of water be removed from hard water?
a. boiling
b. freezing
c. melting
d. none of these
Answer:
a. boiling

B. Fill in the blanks.

Question 1.
Water is called the solvent as it dissolves many substances.
Answer:
Water is called the universal solvent as it dissolves many substances.

Question 2.
The particles of are bigger than those of a colloid.
Answer:
The particles of suspension are bigger than those of a colloid.

Question 3.
A is a heterogeneous solution in which the solute particles are larger than those of a solution and smaller than those of a suspension.
Answer:
A colloid is a heterogeneous solution in which the solute particles are larger than those of a solution and smaller than those of a suspension.

Question 4.
In a solution, no more solute can dissolve at a given temperature.
Answer:
In a saturated solution, no more solute can dissolve at a given temperature.

Question 5.
The process in which the crystals of a solute are separated on cooling a hot saturated solution is called
Answer:
The process in which the crystals of a solute are separated on cooling a hot saturated solution is called crystallization.

Question 6.
A substance that contains water of crystallization is called a substance
Answer:
A substance that contains water of crystallization is called a hydrated substance.

Question 7.
Metal oxides that are soluble in water dissolve in it to form
Answer:
Metal oxides that are soluble in water dissolve in it to form alkalis.

C. Write true or false. Correct the false statements.

Question 1.
Liquids such as petrol and vegetable oil are miscible.
Answer:
True

Question 2.
Chalk powder in water is an example of suspension.
Answer:
True

Question 3.
Blue copper sulphate crystals are anhydrous.
Answer:
False; Blue copper sulphate crystals are hydrated.

Question 4.
Silica gel .is a desiccant
Answer:
True

Question 5.
The reaction of iron with steam is reversible.
Answer:
True

Question 6.
Hard water gives rich lather with soap.
Answer:
False; Soft water gives rich lather with soap.

Question 7.
Limescale is produced when hard water is heated.
Answer:
True

D. Write the chemical equations for the following.

Question 1.
Sodium oxide reacting with water
Answer:
Living Science Chemistry Class 8 ICSE Solution Chapter 8 Water - 1

Question 2.
Potassium reacting with cold water
Answer:
Living Science Chemistry Class 8 ICSE Solution Chapter 8 Water - 2

Question 3.
Aluminium reacting with steam
Answer:
Living Science Chemistry Class 8 ICSE Solution Chapter 8 Water - 3

Question 4.
Heating calcium bicarbonate
Answer:
Living Science Chemistry Class 8 ICSE Solution Chapter 8 Water - 4

Question 5.
Calcium chloride reacting with sodium carbonate
Answer:
Living Science Chemistry Class 8 ICSE Solution Chapter 8 Water - 5

E. Match the columns

1. Universal solvent a. Calcium oxide
2. Desiccant b. Calcium bicarbonate
3. Hygroscopic salt c. Water
4. Magnesium sulphate heptahydrate d. Phosphorus pentoxide
5. Temporary hardness of water e. Potassium nitrate
6. Anhydrous substance f. Hydrated substance
g. Magnesium oxide

Answer:

1. Universal solvent c. Water
2. Desiccant d. Phosphorus pentoxide
3. Hygroscopic salt d. Phosphorus pentoxide
4. Magnesium sulphate heptahydrate f. Hydrated substance
5. Temporary hardness of water b. Calcium bicarbonate
6. Anhydrous substance e. Potassium nitrate

F. Answer the following in short.

Question 1.
Why is water called the universal solvent?
Answer:
Water can dissolve many substances to form aqueous solutions. It can dissolve more substances than any other liquid. Therefore, it is called the universal solvent.

Question 2.
What happens when a carbonated drink bottle is opened?
Answer:
Carbonated drinks contain carbon dioxide dissolved in water at a high pressure. On opening a bottle of a carbonated drink, the dissolved carbon dioxide escapes with a ‘fizz’.

Question 3.
What is a suspension?
Answer:
A suspension is a heterogeneous mixture in which small solid particles are suspended.

Question 4.
Differentiate between a saturated solution and an unsaturated solution.
Answer:
A saturated solution is a solution in which no more solute can dissolve at a given temperature. An unsaturated solution is a solution in which more of the solute can dissolve at a given temperature.

Question 5.
What is crystallization?
Answer:
The process in which the crystals of a solute are separated on cooling a hot saturated solution is called crystallization.

Question 6.
What do you mean by water of crystallization?
Answer:
Water of crystallization is the definite number of water molecules chemically combined with a salt in its crystalline form.

Question 7.
What happens when metal oxides dissolve in water?
Answer:
Metal oxides that are soluble in water dissolve in it to form metal hydroxides.

Question 8.
What are the causes of hardness of water?
Answer:
Hardness of water is caused by dissolved salts of calcium and magnesium such as bicarbonates, chlorides and sulphates.

G Answer the following in detail

Question 1.
Differentiate between a suspension and a colloid.
Answer:
A suspension is a heterogeneous mixture in which small solid particles are suspended. The particles of suspensions can be seen with the naked eye. The particles of a suspension are bigger than those of a solution. Chalk powder in water, flour in milk, smoke emitted by moving vehicles and some medicines are examples of suspensions. A colloid is a heterogeneous solution in which the solute particles are large than those of a solution and smaller than those of a suspension. Milk, cream, toothpaste, blood and ink
are examples of colloids.

Question 2.
How can a saturated solution be converted into an unsaturated one?
Answer:
A saturated solution can also be converted to an unsaturated solution by heating the solution gradually or by adding more of the solvent to it.

Question 3.
Explain the reactions of water with metals with the help of examples.
Answer:
Reactions of metals with water Many metals react with water to produce metal hydroxides or metal oxides and hydrogen gas. With cold water active metals such as potassium, sodium and calcium react with cold water to liberate hydrogen gas and form the corresponding metal hydroxides.
Living Science Chemistry Class 8 ICSE Solution Chapter 8 Water - 6
Living Science Chemistry Class 8 ICSE Solution Chapter 8 Water - 7
With hot water : Magnesium reacts with hot water to form magnesium hydroxide and hydrogen. But, the reaction is slow.
Living Science Chemistry Class 8 ICSE Solution Chapter 8 Water - 8
With steam : When steam is passed over heated magnesium, aluminium, zinc or iron, the corresponding metal oxides and hydrogen gas are produced.
Living Science Chemistry Class 8 ICSE Solution Chapter 8 Water - 9

Question 4.
How can hardness of water be removed? Explain with the help of examples.
Answer:
Removal of hardness of water Temporary hardness of water can be removed by boiling. The soluble bicarbonates of calcium decompose on boiling to form insoluble carbonates. These insoluble salts can be separated from water by filtration and the water then becomes soft.
Living Science Chemistry Class 8 ICSE Solution Chapter 8 Water - 10
Living Science Chemistry Class 8 ICSE Solution Chapter 8 Water - 11

Permanent hardness of water cannot be removed by boiling as it is caused due to chlorides and sulphates of calcium and magnesium. As these salts are stable to heat, permanent hardness can be removed by addition of compounds like washing soda (sodium carbonate). Washing soda reacts with chlorides and sulphates of calcium and magnesium to form their respective insoluble carbonates. The insoluble carbonates can be filtered out and the water becomes soft.
Living Science Chemistry Class 8 ICSE Solution Chapter 8 Water - 12

Question 5.
State the advantages and disadvantages of hard water.
Answer:
Advantages and disadvantages of hard water Hard water has some advantages compared to soft water. For example, the dissolved calcium compounds in hard water can improve the taste of the water. The ions of calcium and magnesium are good for the development and maintenance of bones and teeth. These can help to reduce heart disease.

Hard water also has some disadvantages compared to soft water. For example, hard water unsuitable for washing. More soap is needed to produce lather. With soap, it forms scum that causes wastage of soap. The scum produced spoils the appearance of
baths and shower screens. The scum also sticks to clothes, resulting in the poor washing of the clothes.

Think And Answer

Question 1.
The components of a solution cannot be separated by filtration. Explain.
Answer:
The particles of the solute in a solution are very small and Arundeep’s Living Sci. Chemistry-8th 184
cannot be seen with the naked eye. They are not visible even under a powerful microscope. Solutions are clear and transparent and their components cannot be separated by filtration.

Question 2.
Filter paper can be used to separate the components of a suspension. Why?
Answer:
The particles of a suspension do not pass through filter paper. Thus, filter paper can be used to separate the components of a suspension.

Question 3.
The permanent hardness of water cannot be removed by boiling. Why?
Answer:
The permanent hardness of water cannot be removed by boiling as it is caused due to chlorides and sulphates of calcium and magnesium. As these salts are stable to heat, permanent hardness can be removed by addition of compounds like washing soda (sodium carbonate).

Question 4.
Temporary hardness can reduce the heating efficiency of utensils, industrial boilers and hot water pipes. Explain.
Answer:
Temporary hardness can reduce the heating efficiency of utensils, industrial boilers and hot water pipes. This is because limescale that contains calcium carbonate is produced when hard water is heated. Limescale coats the heating areas in utensils and the inside of boilers and hot water pipes. Because of this, more heat energy is needed to heat water. Pipes may become blocked by limescale causing the heating system to break down.

Living Science Chemistry Class 8 ICSE Solutions

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