Selina Concise Chemistry Class 9 ICSE Solutions Water

Selina Concise Chemistry Class 9 ICSE Solutions Water

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APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 9 Chemistry Chapter 3 Water. You can download the Selina Concise Chemistry ICSE Solutions for Class 9 with Free PDF download option. Selina Publishers Concise Chemistry for Class 9 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Exercise 6(A)

Question 1.
Water exists in all three states. Discuss.
Solution:
In free state, water occurs in three states viz, solid, liquid and gaseous state.

  1. Solid state of water: In solid state, a large amount of fresh water is found in the form of snow or Ice.
  2. Liquid state of water: Most of the water present in oceans, on land water found in streams, rivers, lakes, ponds, springs are also liquid state of water.
  3. Gaseous state of water: In gaseous form, water vapours present in air. When these vapours condense, they form clouds, mist, fog etc. are examples of water in gaseous form.

Question 2.
Why is water considered a compound?
Solution:
Water is considered as a compound because it is made up of two elements, hydrogen and oxygen combined in the ratio of 1 : 8 by mass.
Mass ratio of elements H2O
H : O, 2 X 1 : 16 X 1 = 1 : 8
(Atomic mass of H = 1, O = 16)
And also components of water cannot be separated by physical methods but can be separated by electrolysis of water.

Question 3.
(a) Why does temperature in Mumbai and Chennai not fall as low as it does in Delhi?
(b) Give the properties of water responsible for controlling the temperature of our body.
Solution:
(a) The temperature in Mumbai and Chennai do not fall as low as in Delhi because Mumbai and Chennai are situated at the bank of the oceans due to high specific heat capacity the presence of a large amount of water is able to modify the climate of the nearby land areas are warmer in winter and cooler in summer temperature does not fall wherever Delhi has not same condition.

(b) Our body is almost 65% of water and water has property of specific heat. Due high specific heat capacity the presence of large amount of water is able to modify the climate of the body and control the temperature of our body which is warm in winter and cooler in summer.

Question 4.
Water is the universal solvent’. Comment.
Solution:
Water dissolves many substances forming aqueous solution. It can dissolve solids, liquids and gases. When a solid dissolves in water the solid is said to be solute, the water (the solvent) and the resultant liquid, the solution. So it is said that water is a universal solvent. In other words water can dissolve nearly every substance.

Question 5.
What causes the violence associated with torrential rain?
Solution:
The sudden release of the latent heat of condensation causes the violence associated with torrential rain.

Question 6.
(a) Which property of water enables it to modify the climate?
(b) Density of water varies with temperature. What are its consequences?
(c) What is the effect of impurities present in the water on the melting point and boiling point of water?
Solution:
(a) Specific heat
(b) Water has an unusual physical property. When cooled, it first contracts in volume, as do other liquids, but at 4°C (maximum density), it starts expanding, and continues to do so till the temperature reaches 0°C, the point at which it freezes into ice.
The property of anomalous expansion of water enables marine life to exist in the colder regions of the world, because even when the water freezes on the top, it is still liquid below the ice layer.
Selina Concise Chemistry Class 9 ICSE Solutions Water image - 1

(C) Melting point: The constant temperature at which a solid changes into a liquid state, by absorbing the heat energy is called melting point.

Boiling point: The temperature at which water starts boiling under normal pressure is called boiling point of water.” It is 100°C. Boiling point increases with increase in pressure and vice versa.”

Specific heat capacity: The amount of heat required to raise the temperature of unit mass of that substance through 1°C.

Latent heat of vaporization of water: The energy required to change water into its vapour at its boiling point without any change in temperature is called latent heat of vaporization of water.

Latent heat of vaporization of water is 2260 joules J/g or 540 cal/g.
In the reverse process, 2260 joules of heat is released when 1 g of steam condenses to form 1 g of water at 100°C.
Latent heat of fusion of ice: The amount of heat energy required by ice to change into water is called latent heat of fusion of ice.
Latent heat of fusion of ice is 336 J/g or 80 cal/g.
In the reverse process, 336 joules of heat is released when 1 g of water solidifies to form 1 g of ice at 0°C.

Question 7.
What is the composition of water? In what volume its elements combine?
Solution:
Composition of water :- Hydrogen and Oxygen Volume Ratio = H2 : O
= 2 : 1

Question 8.
The properties of water are different from the properties of the elements of which it is formed. Discuss.
Solution:
The properties of water are different from the properties of elements from which it is formed

PropertyWaterElements – Oxygen and Hydrogen
NatureIt is clear, colourless, odourless, tasteless and transparent liquid.These are colourless,odourless, tasteless and non-poisonous gases.
SolubilityIt can dissolve many things in it and is called universal solvent.Oxygen and hydrogen are slightly soluble in water.
DensityPure water has maximum density at 4°C.Oxygen is heavier than air wherever is the lightest of all the known gases.

Question 9.
How is aquatic life benefited by the fact that water has maximum density at 4oC?
Solution:
The property of anomalous expansion of water enables aquatic life to exist because of the water freezes on top of the surface of the water body, but it is still liquid below the ice layer.

Solution 10.

(a) Aim: To show that tap water contains dissolved salts.

Procedure: Put some tap water on a clean watch glass and place it over a beaker containing water as shown in fig. Boil the water in the beaker. When all the water has evaporated from the watch glass, remove the burner and let it cool. We see at the watch glass against light, a number of concentric rings of solids matter on it. These are dissolved impurities, left behind after evaporation of water. To show that water contains dissolved solids.

Selina Concise Chemistry Class 9 ICSE Solutions Water image - 2

(b) Aim: To show that tap water contains dissolved gases.

Procedure: Take a round bottomed flask and filled it with the tap water. In its mouth fix a delivery tube, in such a way that its lower end of the delivery tube is in line with the under – surface of the cork.

Arrange the apparatus according to diagram.

Heat the flask with the help of a Bunsen burner. It is seen that tiny bubbles of gas are coming out, which stick to the sides of flask, heat it continuously, till the water is about to boil. It is seen that Bubbles of gas start coming out of beehive shelf.

Now lower the flame, to keep the water just near its boiling point. Invert over the beehive shelf a graduated tube, completely filled with tap water. Gradually, the boiled off air, starts collecting in the flask. Collect at least two tubes of boiled off air.

Selina Concise Chemistry Class 9 ICSE Solutions Water image - 3

Question 11.
State the importance of the suitability of CO2 and O2 in water.
Solution:
CO2 and O2 add taste to water for drinking purposes.

Question 12.
How is air dissolved in water different from ordinary air?
Solution:
Oxygen is more soluble in water than nitrogen. Air dissolved in water contains a higher percentage of oxygen. That is, 30% – 35% and in ordinary air it is only 21 %. In this way air dissolved in water is different from ordinary air.

Solution 13.

Rivers and lakes have large amount of water and water has high specific heat capacity, due to which they do not freeze easily.
Even if they freeze, they freeze at top layer. There is water below due to Anomalous expansion of water.

Question 14.
What is the importance of dissolved salts in water?
Solution:
Importance of dissolved salts in water:

  1. Dissolved salts provide a specific taste to water.
  2. Dissolved salts act as micro-nutrients for the growth and development of living beings.

Question 15.
Explain why:
(a) Boiled or distilled water tastes flat.
(b) Ice at zero degrees centigrade has greater cooling effect than water at 0oC.
(c) Burns caused by steam are more severe than burns caused by boiling water.
(d) Rivers and lakes do not freeze easily?
(e) Air dissolved in water contains a higher proportion of oxygen.
(f) If distilled water is kept in a sealed bottle for a long time, it leaves etchings on the surface of the glass.
Rain water does not leave behind concentric rings when boiled.
Solution:
(a) Boiled water tastes flat because boiled water does not contain matter like air, carbon dioxide and other minerals, So the boiled water tastes flat.

(b) Ice at zero degree centigrade gives more cooling effect than water at 0°C because, ice at 0°C absorbs 336J per gram of energy to melt to 0°C water and hence gives more cooling effect.

(c) Burn caused by steam is more severe than burn caused by boiling water because, 1 g of steam contains 2268J more energy than 1 g of boiling water and hence, cause more severe burns.

(d) Rain water does not leave concentric rings when boiled because rain water does not contain dissolved solid, so it does not form concentric rings.

(e) Air dissolved in water contains a higher percentage of oxygen because, solubility of oxygen in water is more than in air. So, air dissolved in water contains a higher percentage of oxygen.

(f) If distilled water is kept in a sealed bottle for a long time, it leaves etching on the surface of glass because, the substances which are insoluble in water, actually dissolve in minute traces in water. Even when we drink water from a glass, an extremely small amount of glass dissolves in water, so we see the etching on the surface of glass when a long time sealed bottle of distilled water poured into the glass.

Question 16.
Explain what you understand from the following diagram:
Selina Concise Chemistry Class 9 ICSE Solutions Water image - 18
Solution:
(i) When solid changes with liquid, it absorbs heat equal to latent heat of fusion and when a liquid changes into solid, it loses heat equal to latent heat of solidification.
(ii) When a liquid changes into gas, it absorbs heat equal to latent heat of vaporization and when a gas condenses into liquid, it loses heat equal to latent heat of condensation.

PAGE NO: 44

Exercise 6(B)

Question 1.
Explain the terms:
(a) Solution
(b) Solute
(c) Solvent
Solution:
(a) Solution: Solution is a homogeneous mixture of two or more substances, components of which cannot be seen separately.
(b) Solute: A solute is the substance that dissolves in a solvent to form a solution.
(c) Solvent: A solvent is a medium in which the solute dissolves.
Solution = Solute + Solvent

Question 2.
Explain why a hot saturated solution of potassium nitrate forms crystals as it cools.
Solution:
The solubility of nitrate decreases with the fall in temperature. Thus, when saturated solution of nitrate is cooled the excess of it separates from solution, in the form of crystals.

Question 3.
Give three factors which affect the solubility of a solid solute in a solvent.
Solution:
The three factors on which the solubility of a solid depends are:

  1. Temperature
  2. Nature of the solid
  3. Nature of solvent

Question 4.
(a) If you are given some copper sulphate crystals, how would you proceed to prepare its saturated solution at room temperature?
(b) How can you show that your solution is really saturated?
Solution:
Take 100 g of distilled water in a beaker. To this add one gram of copper sulphate crystals.

Stir this mixture with the help of a glass rod and dissolve copper sulphate crystals. Similarly, go on dissolving more of copper sulphate, (1 gram) at a time with constant and vigorous stirring. A stage is reached when no more copper sulphate dissolves. It is called saturated solution at this temperature.

Take this saturated solution of copper sulphate some solution in a test tube and add some copper sulphate crystals. The crystals do not dissolve but settle down. This indicates that the solution is really saturated.

Question 5.
(a) Define (i) Henry’s law and (ii) Crystallisation.
(b)State the different methods of crystallisation.
Solution:
(a) (i) Henry’s law: It states that at any given temperatures, the mass of a gas dissolved in a fixed volume of a liquid or solution is directly proportional to the pressure on the surface of a liquid.
(ii) Crystallisation: It is the process by which crystals of a substance separate out on cooling its hot saturated solution.

(b) In the laboratory, crystals may be obtained by the following methods:

  1. By cooling a hot saturated solution gently.
  2. By cooling a fused mass.
  3. By sublimation.
  4. By evaporating slowly a saturated solution.

Question 6.
What would you observe when crystals of copper (II) sulphate and iron (II) sulphate are separately heated in two test tubes?Solution:
Action of heat on copper (II) sulphate crystals
When copper (II) sulphate crystals are heated in a hard glass test tube, the following observations are made.
Selina Concise Chemistry Class 9 ICSE Solutions Water image - 4

  1. The crystals are converted into powdery substance.
  2. The crystals lose their blue coloration on further heating.
  3. Steaming vapour are produced inside the tube which condense near the mouth of the tube to form a colourless liquid.
  4. On further heating, steams escapes from the mouth of the tube and water gets collected in a beaker placed under the mouth of tube.
  5. On further heating, the residue changes to a white powder and steam stops coming out.
    Selina Concise Chemistry Class 9 ICSE Solutions Water image - 5

Action of heat on iron (II) sulphate

When iron (II) sulphate is heated in a test tube, the following observations are made.

  1. The crystals crumble to white powder and a large amount of steam and gas are given out.
  2. On strong heating, a brown residue of ferric oxide (Fe2O3) is produced and a mixture of SO2 and SO3 is given off.
    Selina Concise Chemistry Class 9 ICSE Solutions Water image - 6

Solution 7.

Table salt becomes sticky on exposure during the rainy season because, table salt generally contains a small percentage of Magnesium chloride, as an impurity. Since, these impurities absorb moisture from air due to their deliquescent nature; therefore it gets wet in rainy season and becomes sticky.

Question 8.
What is the effect of temperature on solubility of KNO3 and CaSO4 in water?
Solution:
Potassium nitrate (KNO3): Increase in solubility of substances with rise in temperature.
Calcium sulphate (CaSO4): Decrease in solubility of substances with rise in temperature.

Question 9.
Solubility of NaCl at 40oC is 36.5 g. What is meant by this statement?
Solution:
Solubility of NaCl at 40°C is 36.5 g means 36.5 g of NaCl dissolves in 100 g of water at the temperature of 40°C.

Question 10.
Which test will you carry out to find out if a given solution is saturated or unsaturated or supersaturated?
Solution:

  1. A solution in which more of solute can be dissolved at a given temperature is an unsaturated solution.
  2. A solution in which no more solute can be dissolved at a given temperature is a saturated solution at that temperature.
  3. A solution in which some solute separates on cooling slightly is a super saturated solution.

Question 11.
What is the effect of pressure on solubility of gases? Explain with an example.
Solution:

  • With the increase in pressure the solubility of a gas in water increases.
  • With the increase in temperature, the solubility of a gas in water decreases.
  • For example, The solubility of carbon dioxide in water under normal atmospheric pressure is low, but when the water surface is subjected to higher pressure, a lot more of CO2 gas gets dissolve in it.
  • Similarly, In the case of soda water, on opening the bottle, the dissolved gas rapidly bubbles out, since the pressure on the surface of the water suddenly decreases.

Solution 12.

A solubility curve is a line graph which shows changes in the solubility of a solute in a given solvent with a change in temperature.
To obtain this curve, values of temperature are plotted on X-axis and values of solubility on Y-axis.

Applications:

  1. The variation in the solubility of any given substance with temperature can be studied with the help of solubility curve.
  2. To compare the solubility of different substances, at a given temperature.

Question 13.
Explain why:

  1. Water is an excellent liquid to use in cooling systems.
  2. A solution is always clear and transparent.
  3. Lakes and rivers do not suddenly freeze in the winters.
  4. The solute cannot be separated from a solution by filtration.
  5. Fused CaCl2 or conc. H2SO4 is used in a desiccator.
  6. Effervescence is seen on opening a bottle of soda water.

Solution:

1. Water is an excellent liquid to use in cooling systems due to its ability to absorb large quantities of heat i.e. specific heat = 4.2J/goC, so it is used in cooling system i.e. cooling agent.

2.  A solution is always clear and transparent because in a solution, solid disappeared in water and water has property – cleanliness and transparent. So, the solution is always clean and transparent.

3. Lakes and rivers do not freeze suddenly in winters due to high specific latent heat of solidification. i.e. the amount of heat released when 1 g of water solidifies to form 1 g of ice at 0°C. It is about 336 J/g or 80 cal/g. Such enormous amount of heat leads to immediate freezing of lakes and rivers in winter.

4. The component that actually dissolves in a solvent is known as solute. So it can separated from solution by filtration process. But filtration process is applicable only when solute is insoluble in solution. So the solute cannot be separated from solution by filtration.

5. Fused CaCl2 or concentrated H2SOis deliquescent in nature absorbs moisture and hence, these are used in desiccators or as drying agent.

6. Carbon dioxide is dissolved in soda water under pressure. On opening the bottle, the pressure on the surface of water suddenly decreases, therefore, the solubility of CO2 in water decreases and the gas rapidly bubbles out.

Question 14.
Normally, solubility of crystalline solid increases with temperature. Does it increase uniformly in all cases? Name a substance whose solubility:
(a) Increases rapidly with temperature.
(b) Increases gradually with temperature.
(c) Increases slightly with temperature.
(d) Initially increases then decreases with rise in temperature.
Solution:
(a) Potassium nitrate
(b) Potassium chloride
(c) Sodium chloride
(d) Calcium sulphate

Question 15.
What are drying or desiccating agents? Give examples.
Solution:
These are the substances which can readily absorb moisture from other substances without chemically reacting with them.
For example,
Phosphorus pentoxide (P2O5), quick lime (CaO).

Question 16.
Complete the following table:
Selina Concise Chemistry Class 9 ICSE Solutions Water image - 17
Solution:
Selina Concise Chemistry Class 9 ICSE Solutions Water image - 7

PAGE NO : 45

Question 17.
In which of the following substances will there be
(a) Increase in mass
(b) Decrease in mass
(c) No change in mass when they are exposed to air?

  1. Sodium chloride
  2. Iron
  3. Conc. sulphuric acid
  4. Table salt
  5. Sodium carbonate crystals

Solution:
(a) Increase in mass- Iron and conc. sulphuric acid
(b) Decrease in mass- Sodium carbonate crystals
(c) No change in mass- Sodium chloride

Solution 18.

Selina Concise Chemistry Class 9 ICSE Solutions Water image - 8

Solution 19.

Selina Concise Chemistry Class 9 ICSE Solutions Water image - 9

Solution 20.

Selina Concise Chemistry Class 9 ICSE Solutions Water image - 10
(b) Solubility of solid decreases with fall in temperature. A saturated solution on cooling, a part of dissolved solute separates out in the form of crystals.

(c) Solubility of salt at 293K

KNO3 → 32g
NaCl → 36g
KCl → 35g
NH4Cl → 37 g

(d) At 283K lowest solubility is of KNO3 → 21g

(e) Solubility of most of solids usually increases and of gas and liquid always decreases with rise in temperature.

Solution 21.

(a) Wt. of empty dish = 50 gm
Wt. of dish and solution = 65 gm
Wt. of dish and residue = 54.3 gm
Wt. of saturated solution = 65 – 50 = 15 gm
Wt. of crystals = 54.3 – 50 = 4.3 gm
Wt. of water in saturated solution = 15 – 4.3 = 10.7 gm
Selina Concise Chemistry Class 9 ICSE Solutions Water image - 11

(b) Wt. of water = 50 gm
Solubility at 500oC = 114 gm
Solubility at 30oC = 86 gm
Solubility from 50oC to 30oC = 114 – 86 = 28 gm.
Selina Concise Chemistry Class 9 ICSE Solutions Water image - 12
[Since, Wt. of water = Wt. of solution – Wt. of crystals]
50 g = Wt. of solution – Wt. of crystals
50 + 14 = Wt. of solution
Wt. of solution = 64 gm
Wt. of sodium = Wt. of saturated solution – Wt. of water
= 64 – 50 = 14 gm
Wt. of sodium = 14 gm

Solution 22.

Selina Concise Chemistry Class 9 ICSE Solutions Water image - 13

PAGE NO: 46

Question 1.
What do you understand by

  1. Soft water
  2. Hard water
  3. Temporary hard water
  4. Permanent hard water

Solution 1:

  1. Water is said to be soft when the water containing sodium salts easily gives lather with soap.
  2. Water is said to be hard when it does not readily form lather with soap.
  3. Water which contains only hydrogen carbonates of calcium and magnesium is called temporary hard water.
  4. Water containing sulphates and chlorides of magnesium and calcium is called permanent hard water.

Question 2.
What are the causes for

  1. Temporary hardness
  2. Permanent hardness

Solution:
The presence of hydrogen carbonates of calcium and magnesium makes water temporarily hard.
The presence of sulphates and chlorides of magnesium and calcium makes water permanently hard.

Question 3.
What are the advantages of (i) soft water and (ii) hard water?
Solution:
Advantages of soft water:
When the water is soft, you use much less soap and fewer cleaning products. Your budget will reflect your savings.
Plumbing will last longer. Soft water is low in mineral content and therefore does not leave deposits in the pipes.
Clothes last longer and remain bright longer if they are washed in soft water.
Advantages of hard water:
Water free from dissolved salts has a very flat taste. The presence of salts in hard water makes it tasty. So, hard water is used in making beverages and wines.
Calcium and magnesium salts present in small amounts in hard water are essential for bone and teeth development.
Hard water checks the poisoning of water by lead pipes. When these pipes are used for carrying water, some lead salts dissolve in water to make it poisonous. Calcium sulphate present in hard water forms insoluble lead sulphate in the form of a layer inside the lead pipe and this checks lead poisoning.

Question 4.
What are stalgmites and stalactites? How are they formed?
Solution:
In some limestone caves, conical pillar-like objects hang from the roof and some rise from the floor. These are formed by water containing dissolved calcium hydrogen carbonate continuously dropping from the cracks in the rocks. Release of pressure results in the conversion of some hydrogen carbonate to calcium carbonate.
Ca(HCO3)2 → CaCO3 + CO2 + H2O
This calcium carbonate little by little and slowly deposit on both roof and floor of the cave.
The conical pillar which grows downwards from the roof is called stalactite and the one which grows upward from the floor of the cave is called stalagmite.
These meet after a time. In a year, some grow less than even a centimetre, but some may be as tall as 100 cm.
CaCO3 + CO2 + H2O → Ca(HCO3)2
MgCO3 + CO2 + H2O → Mg(HCO3)2
If the water flows over beds of gypsum (CaSO4.2H2O), a little bit of gypsum gets dissolved in water and makes it hard.

Question 5.
Name the substance which makes water (i) temporarily hard and (ii) permanently hard.
Solution:
Hydrogen carbonates of calcium and magnesium
Sulphates and chlorides of magnesium and calcium

Question 6.
Give equations to show what happens when temporary hard water is

  1. Boiled
  2. Treated with slaked lime

Solution:
Selina Concise Chemistry Class 9 ICSE Solutions Water image - 14

Question 7.
State the disadvantages of using hard water.
Solution:
It is more difficult to form lather with soap.
Scum may form in a reaction with soap, wasting the soap.
Carbonates of calcium and magnesium form inside kettles. This wastes energy whenever you boil a kettle.
Hot water pipes ‘fur up’. Carbonates of calcium and magnesium start to coat the inside of pipes which can eventually get blocked.

Question 8.
What is soap? For what is it used?
Solution:
Soap is chemically a sodium salt of stearic acid (an organic acid with the formula C17H35COOH) and has the formula C17H35COONa.
Soap is used for washing purposes.

Question 9.
What is the advantage of a detergent over soap?
Solution:
Detergents are more soluble in water than soap and are unaffected by the hardness of water as their calcium salts are soluble in water.

Question 10.
Why does the hardness of water render it unfit for use in a (i) boiler and (ii) for washing purposes.
Solution:
Steam is usually made in boilers which are made of a number of narrow copper tubes surrounded by fire. As the cold water enters these tubes, it is immediately changed into steam, while the dissolved solids incapable of changing into vapour deposit on the inner walls of the tubes. This goes on and makes the bore of the tubes narrower. The result is that less water flows through the tubes at one time and less steam is produced. When the bore of the tube becomes very narrow, the pressure of the steam increases so much that at times the boiler bursts.

If hard water is used, calcium and magnesium ions of the water combine with the negative ions of the soap to form a slimy precipitate of insoluble calcium and magnesium usually called soap curd (scum).
Formation of soap curd will go on as long as calcium and magnesium ions are present. Till then, no soap lather will be formed and cleaning of clothes or body will not be possible. Moreover, these precipitates are difficult to wash from fabrics and sometimes form rusty spots if iron salts are present in water.

Question 11.
Explain with equation, what is noticed when permanent hard water is treated with

  1. Slaked time
  2. Washing soda

Solution:
Selina Concise Chemistry Class 9 ICSE Solutions Water image - 15

Question 12.
Explain the permutit method for softening hard water.
Solution:
Permutit is an artificial zeolite. Chemically, it is hydrated sodium aluminium orthosilicate with the formula Na2Al2Si2O8.XH2O. For the sake of convenience, let us give it the formula Na2P.
Selina Concise Chemistry Class 9 ICSE Solutions Water image - 16
A tall cylinder is loosely filled with lumps of permutit. When hard water containing calcium and magnesium ions percolates through these lumps, ions exchange. Sodium permutit is slowly changed into calcium and magnesium permutit, and the water becomes soft with the removal of calcium and magnesium ions.
When no longer active, permutit is regenerated by running a concentrated solution of brine over it and removing calcium chloride formed by repeated washing.
CaP + 2NaCl → Na2P + CaI2

More Resources for Selina Concise Class 9 ICSE Solutions

Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding

Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding

ICSE SolutionsSelina ICSE Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 9 Chemistry Chapter 4 Atomic Structure and Chemical Bonding. You can download the Selina Concise Chemistry ICSE Solutions for Class 9 with Free PDF download option. Selina Publishers Concise Chemistry for Class 9 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

PAGE NO: 55

Question 1.
What is the contribution of the following in atomic structure?

  1. MaharshiKanada
  2. Democritus

Solution:
According to Maharshi Kanada:
Matter consisted of indestructible particles called paramanus (now called atoms).
A paramanu does not exist in the free state, rather it combines with other paramanus to form a bigger particle called the anu (now called a molecule).
Democritus called paramanu as atom which comes from the Greek word atomos, meaning indivisible.

Question 2.
State Dalton’s atomic theory.
Solution:
Main postulates of Dalton’s atomic theory:

  • Matter consists of very small and indivisible particles called atoms.
  • Atoms can neither be created nor be destroyed.
  • The atoms of an element are alike in all respects, but they differ from the atoms of other elements.
  • Atoms of an element combine in small numbers to form molecules.
  • Atoms of one element combine with atoms of another element in a simple ratio to form molecules of compounds.
  • Atoms are the smallest units of matter which can take part in a chemical reaction.

Question 3.
What is an α (alpha) particle?
Solution:
An α-particle is a doubly charged helium ion (He2+) containing two protons and two neutrons. It is formed by removing two electrons from the helium atom.

Question 4.
What are cathode rays? How are these rays formed?
Solution:
Cathode rays are the beam of electrons which travel from the negatively charged end (i.e. cathode to anode) of a vacuum tube, across a voltage difference between the electrodes placed at each end.
Formation of cathode rays:
Generally gases are poor conductors of electricity. However, when a high voltage charge from an induction coil is applied to tubes filled with gases at very low pressure (0.01 mm of mercury), the gases become good conductors of electricity and begin to flow in the form of rays.
These rays are called cathode rays and they travel from the cathode towards the anode.
Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 1

Question 5.
What is the nature of the charge on

  1. Cathode rays and
  2. Anode rays?

Solution:
Cathode rays are negatively charged as they consist of negatively charged particles called electrons.
Properties of cathode rays:

  • They travel from the cathode to the anode in straight lines.
  • They cause a greenish yellow fluorescence on a soda-glass screen placed in the tube.
  • They are affected by an electric field, i.e. they are inflected towards the positive field and deflected from the negative field. This shows that they carry a negative charge.
  • When a beam of cathode rays is made to fall upon hard metallic targets like tungsten, X rays are produced.
  • They penetrate matter.
  • They cause ionisation of the gas through which they pass.
  • The ratio of the charge (s) to mass (m) of the particles constituting cathode rays remains the same (e/m = 1.76 × 1011 coulomb/kg) irrespective of the nature of the gas taken and of the metal forming the cathode.
  • They produce the shadow of an opaque object placed in their path and make a light paddle wheel rotate.

Question 6.
How are X-rays produced?
Solution:
When a beam of cathode rays is made to fall upon hard metallic targets like tungsten, X-rays are produced.

Question 7.
Why are anode rays also called as ‘canal rays’?
Solution:
When perforated rays were used in the discharge tube, another set of rays travelling in a direction opposite to that of the cathode rays, i.e. from the anode towards the cathode, is seen, as in the figure below. These rays are called canal rays because they passed through the holes or canals in the cathode. These rays were named positive rays or anode rays.
Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 2

Question 8.
How does cathode ray differ from as anode rays?
Solution:
Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 3

Question 9.
State one observation which shows that atom is not indivisible.
Solution:
Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 4

Question 10.

  1. Name an element which does not contain neutron
  2. If an atom contains one electron and one proton, will it carry as a whole is neutral

Solution:

  • Hydrogen does not contain any neutron.
  • No. It is neutral.

Question 11.
On the basis of Thomson’s model of an atom explain how an atom as a whole is neutral.
Solution:
Thomson’s Atomic Model:
According to Thomson’s atomic model, an atom is made of positively charged substances in the form of a sphere. Electrons are embedded into this sphere, and the total positive charge of the sphere is equal to the total negative charge of electrons, and hence, the atom remained electrically neutral. This model was not accepted because it was unable to explain how positively charged particles were shielded from negatively charged particles without getting neutralised.
Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 5

Question 12.
Which sub-atomic particle was discovered by

  1. Thomson
  2. Goldstein
  3. Chadwick

Solution:

  • Thomson discovered particles.
  • Goldstein discovered protons.
  • Chadwick discovered neutrons.

Question 13.
Name the sub-atomic particle whose charge is:

  1. +1
  2. -1
  3. 0

Solution 13:

  • Proton
  • Electron
  • Neutron

Solution 14:
Rutherford selected gold metal because he wanted as thin a layer as possible, and gold is the most malleable metal.
Heavy metals such as platinum will show the same observation with alpha particles as shown by gold foil.
If a light nucleus like lithium is used, then fast-moving alpha particles may even push the light nucleus aside and may not be deflected back.

Question 15.
On the basis of Rutherford’s model of an atom, which subatomic particle is present in the nucleus of an atom?
Solution:
According to Rutherford’s model of an atom, the subatomic particle in a nucleus is a proton.

Question 16.
Which part of atom was discovered by Rutherford?
Solution:
The nucleus was discovered by Rutherford.

Question 17.
How was it shown that atom has empty space?
Solution:
Rutherford performed an experiment by allowing a stream of alpha particles to pass through a very thin gold foil. He observed that alpha particles pass through the metal foil without deviating from their path. This shows that an atom contains a large empty space called nuclear space.

Question 18.
State one major drawback of Rutherford’s model
Solution:
One major drawback of Rutherford’s model was the comparison of electrons with the planets in the solar system.
Thus, when an electron moved around the nucleus continually, it should radiate energy, i.e. lose energy. As a result it should be gradually pulled towards the nucleus and end up colliding with it. This should result in the total collapse of the atom.
However, we know that the atom is structurally stable. Thus, Rutherford’s model could not explain this stability.

Question 19.
In the figure given alongside

  1. Name the shells denoted by A,B, and C. Which shell has least energy
  2. Name X and state the charge on it
  3. The above sketch is of …………. Model of an atom
    Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 32

Solution:
A is for K shell or I shell.
B is for L shell or II shell.
C is for M shell or III shell.
Shell K has the minimum amount of energy.
X is a nucleus; it is positively charged.
The above sketch is of Bohr model of an atom.

Question 20.
Give the postulates of Bohr’s atomic model
Solution:
Atom has a central nucleus surrounded by electrons.
The electrons revolve around the nucleus in definite circular paths called orbits.
Each orbit has fixed energy. Therefore, these orbits are also known as energy levels or energy shells.
These orbits or energy levels are represented either by a number 1, 2, 3,… known as the principal quantum number (n) of the orbit or by K, L, M,….
There is no change of energy of electrons as long as they keep revolving in the same energy level and the atom remains stable. Electrons can jump from the higher orbit to the lower orbit when they lose energy and jump to the next when they gain energy.

PAGE NO: 59

Question 1.

  1. Name the three fundamental particles of an atom.
  2. Give the symbol and charge of each particle.

Solution:
Symbol     Charge
Electron           e1-           -1
Proton             p1+         +1
Neutron            n              0
i. Electron 20
ii. Neutron 20
iii. Proton 20

Question 2.
Complete the table given below by identifying P, Q, R and S.
Selina Concise Chemistry Class 9 ICSE Solutions Water image - 20
Solution:
Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 6

Question 3.
The atom of an element is made up of 4 protons, 5 neutrons and 4 electrons. What are its atomic number and mass number?Solution:
Atomic number = Number of protons or number of electrons = 4
Mass number = Number of protons + Number of neutrons = 4 + 5 = 9

Question 4.
The atomic number and mass number of sodium are 11 and 23 respectively. What information is conveyed by this statement?Solution:
Atomic number (11) of sodium conveys information that the number of protons and electrons is the same.
Mass number (23) of sodium indicates the sum of protons and neutrons.

Question 5.
Write down the names of the particles represented by the following symbols and explain the meaning of superscript and subscript numbers attached
Selina Concise Chemistry Class 9 ICSE Solutions Water image - 21
Solution:
p = proton
n = neutron
e = electron
Superscript number : These superscript number show their mass number
Subscript number : These numbers show their atomic number

Question 6.
From the symbol, Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 33state the mass number, the atomic number and electronic configuration of magnesium
Solution:
Mass number = 24
Atomic number = 12
No. of electrons = 24 – 12 = 12
Electronic configuration = 2, 8, 2

Question 7.
Sulphur has an atomic number 16 and a mass of 32.
State the number of protons and neutrons in the nucleus of sulphur. Give a simple diagram to show the arrangement of electrons in an atom of sulphur.
Solution:
Atomic number = 16
Atomic mass = 32
Number of protons = 16
Number of electrons = 16
Number of neutrons = 32 – 16 = 16
Electronic configuration = 2, 8, 6
Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 22

Question 8.
Explain the rule according to which electrons are filled in various energy levels.
Solution:
The maximum capacity of a shell to accommodate electrons is given by the general formula 2n2, where n is the serial number of a shell.
The maximum number of electrons possible in the outermost shell is 8 and that in the penultimate shell is 18.
It is not necessary for an orbit to be completed before another is formed. In fact, a new orbit is formed when the outermost shell attains 8 electrons.

Question 9.
Draw the orbital diagram of Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 23ion and state the number of three fundamental particles present in it.
Solution:
Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 7

PAGE NO: 62

Question 1.
How does the Modern atomic theory contradict and correlate with Dalton’s atomic theory?
Solution:
The latest research on the atom has proved that most of the postulates of Dalton’s atomic theory contradict. However, Dalton was right that atoms take part in chemical reactions.
Comparisons of Dalton’s atomic theory with the modern atomic theory.

  1. Dalton’s atomic theory:
    • Atoms are indivisible.
    • Atoms of the same element are similar in every respect.
    • Atoms combine in a simple whole number ratio to form molecules.
    • Atoms of different elements are different.
    • Atoms can neither be created nor be destroyed.
  2. Modern atomic theory:
    • Atoms are no longer indivisible and consist of electrons, protons, neutrons and even more sub-particles.
    • Atoms of the same element may differ from one another called isotopes.
    • Atoms of different elements may be similar called isobars.
    • Atoms combine in a ratio which is not a simple whole number ratio; e.g. in sugar, the C12H22O11 ratio is not a whole number ratio.

Question 2.

  1. What are inert elements?
  2. Why do they exist as monoatoms in molecules?
  3. What are valence electrons?

Solution:
The elements have a complete outermost shell, i.e. 2 or 8 electrons. They ordinarily do not enter into any reaction.
These exist as monoatoms because molecules of these elements contain only one atom.
Valence electrons: The number of electrons present in the valence shell is known as valence electrons.

Question 3.
In what respects do the three isotopes of hydrogen differ? Give their structures.
Solution:
The three isotopes differ only due to their mass number which is respectively 1, 2 and 3 and named protium, deuterium and tritium.
Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 8

Question 4.
Match the atomic numbers 4,14,8,15 and 19 with each of the following:

  1. A solid non-metal of valency 3.
  2. A gas of valency 2.
  3. A metal of valency 1.
  4. A non-metal of valency 4.

Solution:
Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 9

Question 5.
Draw diagrams representing the atomic structures of the following:

  1. Sodium atom
  2. Chlorine ion
  3. Carbon atom
  4. Oxygen ion

Solution:
Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 10

Question 6.
What is the significance of the number of protons found in the atoms of different elements?
Solution:
The number of protons in the nucleus of an atom determines the element type of the atom.

Question 7.
Elements X, Y and Z have atomic numbers 6,9 and 12 respectively. Which one:
(a) Forms an onion
(b) Forms a cation
(c) Has four electrons in its valence shell?
Solution:
Atomic numbers of
X 6 (2, 4)
Y 9 (2, 7)
Z 12 (2, 8, 2)
Y(2, 7) forms an anion.
Z(2, 8, 2) forms a cation.
X(2, 4) has four electrons in the valence shell.

Question 8.
Element X has electronic configuration 2,8,18,8,1. Without identifying X,

  1. Predict the sign and charge on a simple ion of X.
  2. Write if X will be an oxidizing agent or a reducing agent. Why?

Solution:
X1+
Oxidising agent, because it has the ability to donate electrons.

Question 9.
Define the terms:

  1. Mass number
  2. Ion
  3. Cation
  4. Anion
  5. Element
  6. orbit

Solution:
Mass number is the sum of the number of protons and the number of neutrons in the nucleus of an atom.
Ion is an atom or molecule which carries a positive or negative charge because of loss or gain of electrons.
Cation is a positively charged ion which is formed when an atom loses one or more electrons; for example, Na+, Hg2+ and Ca2+.
Anion is a negatively charged ion which is formed when an atom gains one or more electrons; for example, Cl and I.
Element is a substance which cannot be split up into two or more simple substances by usual chemical methods of applying heat, light or electric energy; for example, hydrogen, oxygen and chlorine.
Orbit is a circular path around the nucleus in which electrons of the atom revolve.

Question 10.
From the symbol Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 24for the element helium, write down the mass number and the atomic number of the element
Solution:
Atomic number = 2
Mass number = 4

Question 11.
Five atoms are labeled A to E
Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 25

(a) Which one of these atoms:
i. contains 7 protons
ii. has electronic configuration 2,7
(b) Write down the formula in the compound formed between C and D
Predict : (i) metals (ii) non-metals

Solution:

  • Atom E contains 7 protons.
    Atom B has an electronic configuration 2, 7.
  • Atom C stands for 7Li3, Atom D stands for 8O16.
    Hence, compound formula is Li2O.
  • Metals: A and C, Non-metals: B, D, E

Question 12.
An atom of an element has two electrons in the M shell.
What is the (a) atomic number (b) number of protons in this element?
Solution:
Number of electrons in the M shell = 2
So, the number of electrons in the K and L shells will be = 2, 8
Hence, atomic number = 2 + 8 + 2 = 12
Number of protons = 12

PAGE NO : 63

Question 13
Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 26
Solution:
Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 11

Question 14.
What are nucleons? How many nucleons are present in phosphorus? Draw its structure.
Solution:
Nucleons: Particles which constitute the nucleus are called nucleons.
Protons and neutrons are the nucleons.
Atomic mass of phosphorus = 31
Atomic number = 15
Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 12

Question 15.
What are isotopes? With reference to which fundamental particle do isotopes differ? Give two uses of isotopes.
Solution:
Isotopes: Atoms of the same element having the same atomic number but different mass numbers.
Isotopes differ with reference to neutrons.
Uses of isotopes:
Some isotopes are radioactive, i.e. isotopes of cobalt are used for treating cancer and other diseases.
An isotope of 235U is used as a fuel in a nuclear reactor.

Question 16.
Why do Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 27 have the same chemical properties? In what respect do these atoms differ?
Solution:
Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 13

Question 17.
Explain fractional atomic mass. What is the fractional mass of chlorine?
|Solution:
Atomic masses of the isotopes of chlorine are 35 and 37. However, in any given sample of chlorine gas, the isotopes occur in the approximate ratio 3:1, 75% of Cl35 and 25% of Cl37. So, the relative atomic mass or atomic weight of chlorine is 35.5.
Fractional atomic mass of chlorine
At. Mass = (3(35) + 1(37)) / 2 = (105 + 37) / 2

Question 18.
(a) What is meant by ‘atomic number of an element”?
(b) Complete the table given below
Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 28
(c) Write down the electronic configuration of (i) chlorine atom (ii) chlorine ion
Solution:
Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 14

Question 19.
Name the following:

  1. The element which does not contain any neutron in its nucleus.
  2. An element having valency ‘zero’
  3. Metal with valency 2
  4. Two atoms having the same number of protons and electrons but different number of neutrons.
  5. The shell closest to the nucleus of an atom

Solution:
Hydrogen
Helium
Magnesium
Hydrogen and carbon
K

Question 20.
Give reasons
(a) Physical properties of isotopes are different.
(b) Argon does not react.
(c) Actual atomic mass is greater than mass number.
Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 29
Solution:
Physical properties depend on atomic mass, and isotopes have different mass number, i.e. they have different number of neutrons. So, isotopes have different physical properties.
Argon does not react as it has the outermost orbit complete, i.e. 8 electrons in the outermost shell.
Actual atomic mass is greater than the mass number because the mass number is a whole number approximation of atomic mass unit. In fact, neutrons are slightly heavier than protons, and an atom has over 200 sub-atomic particles.
are isotopes of chlorine element which differ in the number of neutrons, whereas chemical properties are determined by the electronic configuration of an atom. Isotopes of an element are chemically alike.

Question 21.
An element A atomic number 7 mass numbers 14
B electronic configuration 2,8,8
C electrons 13, neutrons 14
D Protons 18 neutrons 22
E Electronic configuration 2,8,8,1
State (i) Valency of each element (ii) which one is a metal (iii) which is non-metal (iv) which is an inert gas
Solution:

  • Element A
    Atomic number = 7 = Number of electrons = 2, 5
    Valency of A = 8 – 5 = 3
    Element B
    Electronic configuration 2, 8, 8
    Valency of B = Zero
    Element C has 13 electrons
    Electronic configuration = 2, 8, 3
    Valency of C = 3
    Element D
    Protons = 18 = Electrons = 2, 8, 8
    Valency of D = Zero
    Element E
    Electronic configuration = 2, 8, 8, 1
    Valency of E = 1
  • C and E are metals.
  • A is a non-metal.
  • A, C and E are not inert gases.

Question 22.
Choose the correct option
(a) Rutherford’s alpha-particle scattering experiment discovered

  1. Electron
  2. Proton
  3. Atomic nucleus
  4. Neutron

(b) Number of valence electrons in O2- is :

  1. 6
  2.  8
  3. 10
  4. 4

(c) Which of the following is the correct electronic configuration of potassium?

  1. 2,8,9
  2. 8,2,9
  3. 2,8,8,1
  4. 1,2,8,8

Solution:
Atomic nucleus
[6]
[2, 8, 8, 1]

Question 23.
Explain

  1. Octet rule for formation of sodium chloride
  2. Duplet rule for formation of hydrogen

Solution:
Elements tend to combine with one another to attain the stable electronic configuration of the nearest inert gas.

  • Sodium chloride
    Sodium atom has 1 electron in the valence shell which it donates to the chlorine atom with 7 electrons in the valence shell to attain the stable electronic configuration of the nearest inert gas, i.e. 8 electrons in the valence shell. This is known as the octet rule. These elements combine to form sodium chloride.
  • Hydrogen
    Hydrogen atom has one electron in the valence shell which it shares with another hydrogen atom having one electron to complete its duplet state, i.e. two electrons in the valence shell and resulting in the formation of hydrogen.

Question 24.
Complete the following table relating to the atomic structure of some elements.
Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 30
Solution:
Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 15

PAGE NO: 67

Question 1.
How do atoms attain noble gas configurations?
Solution:
Combining atoms attain the noble gas configuration by transferring or sharing electrons.

Question 2.
Define electrovalent bond.
Solution:
A chemical bond may be defined as the force of attraction between any two atoms in a molecule to maintain stability.
The chemical bond formed due to the electrostatic force of attraction between a cation and an anion is called an electrovalent bond.
The chemical bond formed between two combining atoms by mutual sharing of one or more pairs of electrons is called a covalent bond.

Question 3.
Elements are classified as metals, non-metal, metalloids and inert gases. Which of them form electrovalent bond?
Solution:
Conditions for the formation of an ionic bond:

  • Ionisation potential (IP)
    Lower the value of IP of a metallic atom, greater the ease of formation of the cation.
  • Electron affinity
    Higher the value of EA of a non-metallic atom, greater the ease of formation of the anion.
  • Electronegativity
    Larger the electronegativity difference between combining atoms, greater the ease of electron transfer.

Question 4.
(a) An atom X has three electrons more than the noble gas configuration. What type of ion will it form?
(b) Write the formula of its (X)

  1. sulphate
  2. nitrate
  3.  iii. phosphate
  4. carbonate
  5. hydroxide.

Solution:
It will form a positive ion, i.e. cation.

  • X(SO4)3
  • X(NO3)3
  • XPO4
  • X2(CO3)3
  • X(OH)3

Question 5.
Mention the basic tendency of an atom which makes it to combine with other atoms
Solution:
Besides chaos, everything in this world wants stability. The same is the case with atoms. For atoms, stability means having the electron arrangement of an inert gas, i.e. octet in the outermost shell. Helium has two electrons (duplet), while all other inert gases, i.e. neon, argon, krypton, xenon and radon have eight electrons (octet) in the outermost shell.

Question 6.
What type of compounds are usually formed between metals and non-metals and why?
Solution:
Electrovalent compounds are usually formed between metals and non-metals.
Atoms of metallic elements which have 1, 2 or 3 valence electrons can lose electron(s) to atoms of non-metallic elements which have 5, 6 or 7 valence electrons and thereby form an electrovalent bond.

Question 7.

  1. In the formation of the compound XY2, an atom X gives one electron to each Y atom. What is the nature of bond in XY2?
  2. Draw the electron dot structure of this compound.

Solution:

  1. Nature of bond in XY2 is an ionic bond.
  2. Electron dot structure of XY2:

Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 31

Question 8.
An atom X has 2, 8, 7 electrons in its shell. It combines with Y having 1 electron in its outermost shell.

  1. What type of bond will be formed between X and Y?
  2. Write the formula of the compound formed.

Solution:
Ionic bond
XY

Question 9.
Draw orbit structure diagram of sodium chloride (NaCl) and calcium oxide (CaO).
Solution:
Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 17
Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 18

Question 10.
Compare :

(a) Sodium atom and sodium ion

(b) Chlorine atom and chloride ion, with respect to

  1.  Atomic structure
  2. Electrical state

Solution 10:
Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 19
In chlorine atom, the number of protons (17) is equal to the number of electrons (17).
In chloride ion, there are 17 protons but 18 electrons.
Chlorine atom is electrically neutral. Chloride ion is negatively charged.
Chlorine atom is reactive. It reacts with sodium vigorously forming sodium chloride. Chloride ion is unreactive. It does not react with sodium.
Chlorine (Cl2) is a poisonous, toxic, corrosive gas which is used in the manufacture of bleaching agents and disinfectants. It is non-toxic and readily adsorbed by plants.

Question 11.
The electronic configuration of fluoride ion is the same as that of neon atom. What is the difference between the two?
Solution:
Fluoride ion is a negatively charged ion with 9 protons and 10 electrons.
Neon atom is electrically neutral with 10 protons and 10 electrons.

Question 12.
  1. What do you understand by redox reactions?
  2. Explain oxidation and reduction in terms of loss or gain of electrons.

Solution 12:
Transfer of electron(s) is involved in the formation of an electrovalent bond. The electropositive atom undergoes oxidation, while the electronegative atom undergoes reduction. This is known as a redox process.
Oxidation: In the electronic concept, oxidation is a process in which an atom or ion loses electron(s).
Zn → Zn2+ + 2e
Reduction: In the electronic concept, reduction is a process in which an atom or ion accepts electron(s).
Cu2+ + 2e → Cu

  • Zn → Zn2++ 2e (Oxidation)
    Pb2+ + 2e → Pb (Reduction)
  • Zn → Zn2+ + 2e (Oxidation)
    Cu2+ + 2e→ Cu (Reduction)
  • Cl+ 2e →2Cl (Reduction)
    2Br → Br2 + 2e (Oxidation)
  • Sn2+ → Sn4+ + 2e (Oxidation)
    2Hg2+ + 2e → Hg2 (Reduction)
  • Cu+ → Cu2+ + e (Oxidation)
    Cu+ + e → Cu (Reduction)
Question 13.
Potassium (at No.19) and chlorine (at No.17) react to form a compound. Explain on the basis of electronic concept:
i. Oxidation
ii. Reduction
iii. Oxidizing agent
iv. Reducing agent

2K + Cl2 → 2KCl

  • Oxidation: In the electronic concept, oxidation is a process in which an atom or ion loses electron(s).
    K → K+ + e
  • Reduction: In the electronic concept, reduction is a process in which an atom or ion accepts electron(s).
    Cl2 + 2e→ 2Cl
  • Oxidising agent
    An oxidising agent oxidises other substances either by accepting electrons or by providing oxygen or an electronegative ion, or by removing hydrogen or an electropositive ion.
    Cl2 + 2e→ 2Cl
  • Reducing agent
    A reducing agent reduces other substances either by providing electrons or by providing hydrogen or an electropositive ion, or by removing oxygen or an electronegative ion.
    K → K+ + e

PAGE NO: 73

Solution 1:
They are good conductors of electricity in the fused or aqueous state because electrostatic forces of attraction between ions in the solid state are very strong and these forces weaken in the fused state or in the solution state. Hence, ions become mobile.
In electrovalent compounds, there exists a strong force of attraction between the oppositely charged ions, so a large amount of energy is required to break the strong bonding force between ions. So, they have high boiling and melting points.
In covalent compounds, they have weak forces of attraction between the binding molecules, thus less energy is required to break the force of binding. So, they have low boiling and melting points.
As water is a polar compound, it decreases the electrostatic forces of attraction, resulting in free ions in aqueous solution. Hence, electrovalent compounds dissolve.
Covalent compounds do not dissolve in water but dissolve in organic solvents. Organic solvents are non-polar; hence, these dissolve in non-polar covalent compounds.
Electrovalent compounds are usually hard crystals yet brittle because they have strong electrostatic forces of attraction between their ions which cannot be separated easily.
Polar covalent compounds conduct electricity because they form ions in their solutions.

Solution 2:
The nature of the solid is ionic.
Ionic compounds are hard crystalline solids with high melting points because of a strong force of attraction between the oppositely charged ions. So, a large amount of energy is required to break the strong bonding force between ions.
Electrovalent compounds are soluble in water. As water is a polar compound, it decreases the electrostatic forces of attraction, resulting in free ions in aqueous solution. Hence, they dissolve.

Question 3
Match the atomic numbers 4,8,10,15 and 19 with each of the following:

  1. Element which can form trivalent ion
  2. Element with four shells
  3. Element with 6 valence electrons
  4. Element which does not form ion

Solution:
15
8
19
10

Question 4.
(a) Elements X,Y and Z have atomic numbers 6,9 and 12 respectively. Which one:

  1. Forms an anion
  2. Forms a cation

(b) State the type of bond between Y and Z and give its molecular formula.
Solution:
i. Y = 9
ii. Z = 12
Ionic bond with molecular formula ZY2.

Question 5.
Taking MgCl2 as an electrovalent compound, CCl4 as a covalent compound, give four difference between electrovalent and covalent compounds
Solution:
Selina Concise Chemistry Class 9 ICSE Solutions Atomic Structure and Chemical Bonding image - 20

Question 6.
Potassium chloride is an electrovalent compound, while hydrogen chloride is covalent compound, But, both conduct electricity in their aqueous solutions. Explain.
Solution:
Potassium chloride is an electrovalent compound and conducts electricity in the molten or aqueous state because the electrostatic forces of attraction weaken in the fused state or in aqueous solution.
Polar covalent compounds like hydrogen chloride ionise in their solutions and can act as an electrolyte. So, both can conduct electricity in their aqueous solutions.

Question 7.
Name two compounds that are covalent when taken pure but produce ions when dissolved in water.
Solution:
HCl and NH3
HCl + H2O → H3O+ + Cl
NH3 + H2O →NH4+ + OH

Question 8.
An element M burns in oxygen to form an ionic compound MO. Write the formula of the compounds formed if this element is made to continue with chlorine and sulphur separately.
Solution:
Formula of compound when combined with sulphur – MS
Formula of compound when combined with chlorine – MCl2

Solution 9:

Question 10.
State the type of bonding in the following molecules.

  1. Water,
  2. Calcium oxide
  3. Hydrogen chloride

Solution:
Polar covalent bond
Ionic bond
Polar covalent bond

Question 11.
Element M forms a chloride with the formula MCl2 which is a solid with high melting point. What type of bond is in MCl2 . Write the formula of the compound when M combine with sulphur, oxygen and nitrogen.
Solution:
The bond formed between metal and nonmetal is ionic bond.
Bond formed between metal M and chlorine is ionic bond.
When metal M combines with sulphur – MgS
When metal M combines with  oxygen – MgO
(b) Mg

Solution 12:
C. Covalent
C. Low melting point and low boiling point
D. Not conduct electricity
Y is getting reduced.
Anode

Solution 13:
B. It has a high melting point.
A. It loses electrons and is oxidised.

Question 14.
Identify the following reactions as either oxidation or reduction:

  1. O + 2e → O2-
  2. K – e → K+
  3. Fe3+ + e → Fe2+
  4. Zn → Zn2+ + 2e-

Solution:
Reduction
Oxidation
Reduction

Question 15.

  1. Name the charged particles which attract one another to form electrovalent compounds.
  2. In the formation of electrovalent compounds, electrons are transferred from one element to another. How are electrons involved in the formation of a covalent compound?
  3. The electronic configuration of nitrogen is (2, 5). How many electrons in the outer shell of a nitrogen atom are not involved in the formation of a nitrogen molecule?
  4. In the formation of magnesium chloride (by direct combination between magnesium and chlorine), name the substance that is oxidized and the substance that is reduced.

Solution:
Cation and anion
By mutual sharing of electrons
Two
Magnesium is oxidised and chlorine is reduced.

PAGE NO : 74
Solution 16:
C. Consists of oppositely charged ions
Covalent bond

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Frank ICSE Solutions for Class 10 Chemistry – Metals and Non-metals

Frank ICSE Solutions for Class 10 Chemistry – Metals and Non-metals

PAGE NO : 151
Solution 1:
Frank ICSE Solutions for Class 10 Chemistry - Metals and Non-metals 1

Solution 2:
Frank ICSE Solutions for Class 10 Chemistry - Metals and Non-metals 2

Solution 3:
Metal which exist in liquid state is mercury.
Non-metal which exist in liquid state is bromine.
Concept Insight: Metals are usually solid while non-metals exist in all the three states.

Solution 4:
The most abundant metal in the earth’s crust is aluminium and the most abundant non-metal in the earth’s crust is oxygen.

Solution 5:

  1. Metals.
  2. Non-metals.
  3. Platinum and Gold.
  4. Potassium and Sodium.
  5. Potassium, Sodium and Calcium.
  6. Iron.
  7. Potassium and Sodium.
  8. Platinum.
  9. Platinum and Gold.
  10. Mercuric oxide (HgO) and Silver oxide (Ag2O).
  11. Potassium hydroxide (KOH) and Sodium hydroxide (NaOH).
  12. Potassium carbonate (K2CO3) and Sodium carbonate (Na2CO3).
  13. Potassium carbonate (K2CO3) and Sodium carbonate (Na2CO3).
  14. Potassium nitrate (KNO3) and Sodium nitrate (NaNO3).
  15. Mercuric nitrate (Hg(NO3)2) and silver nitrate (AgNO3)

Solution 6:
Frank ICSE Solutions for Class 10 Chemistry - Metals and Non-metals 3

Solution 7:

  1. Fe < Zn < Mg < Na.
  2. Na = Al < Cu<Fe
  3. Ca >Mg > Fe > Cu.

Solution 8:
Frank ICSE Solutions for Class 10 Chemistry - Metals and Non-metals 4

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Frank ICSE Solutions for Class 10 Chemistry – Metallurgy

Frank ICSE Solutions for Class 10 Chemistry – Metallurgy

PAGE NO : 152
Solution 9:
Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 1
Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 2

Solution 10:
Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 3

Solution 11:
Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 4

Solution 12:

  1. Aqueous solution of sodium chloride is not used for electrolytic reduction of sodium metal because sodium metal formed at cathode after discharge of sodium ions( at cathode) will react with water to form alkali NaOH.
  2. For the reduction of a metal oxide a reducing agent other than carbon is carbon monoxide (CO).

 

Solution 13:
Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 5

PAGE NO : 169

Solution 1:

  1. Gold and Platinum.
  2. Charge.
  3. Gangue.
  4. Flux.
  5. Calcination.
  6. Roasting.
  7. Iron pyrites.
  8. Bauxite.
  9. Cryolite, aluminium fluoride, Calcium fluoride.
  10. Cathode: inner lining of gas-carbon of the electrolytic cell.
    Anode: Thick carbon rods dipping into the fused electrolytes.
  11. Thermite welding.
  12. Copper and silver.
  13. Aluminium, Iron.
  14. platinum and gold
  15. sodium and potassium

Solution 2:

  1. Zinc is used in galvanization and dry cells because zinc coating protects the iron from corrosion as it is more electropositive than iron hence it would be attacked first.
  2. Nitric acid can be stored in aluminium containers because it do not attack aluminium. It renders aluminium passive due to the formation of an oxide film on surface of aluminum.
  3. Aluminium oxide cannot be reduced by carbon because it is comparatively high in electrochemical series hence more reactive than carbon.
  4. A neutral gas other than oxygen is formed at the anode during electrolysis of fused alumina because the oxygen gas formed at the anode oxidizes the carbon of the anode to carbon dioxide.
  5. Extraction of aluminium was very difficult in the beginning because it was very expensive.
  6. Carbon anodes are used in the electrolytic extraction of aluminium because carbon in the form of graphite is a good conductor of electricity.
  7. Galvanized metal ions should not be used for storing food as food acids may react with the zinc coating and cause food poisoning.

Solution 3:

  1. Mineral: The naturally occurring compounds of metals which are generally mixed with earthy such as soil, sand, limestone and rocks are known as minerals.
  2. Ore: Those minerals from which a metal can be extracted profitably are called ores.
  3. Gangue: The rocky impurities like (SiO2) present in an ore are called gangue.
  4. Charge: The mixture of materials fed into a furnace to extract a metal is called charge.
  5. Flux: The substance added to get rid of gangue in the extraction of metal is called flux.
  6. Slag: The product obtained by the combination of gangue with flux is called slag.

PAGE NO : 170
Solution 4:
Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 6

Solution 5:

  1. Mercury.
  2. Silver.
  3. Zinc.
  4. Aluminium.

Solution 6:
As we know that minerals are the naturally occurring compounds of metals which are generally mixed with earthy such as soil, sand, limestone and rocks while ores are those minerals from which a metal can be extracted profitably.
Hence “All ores are minerals but all minerals are not ores”.

Solution 7:

  1. Iron: Haematite(Fe2O3) and Magnetite (Fe3O4).
  2. Zinc: Zinc blende (ZnS) and Calamine (ZnCO3).
  3. Aluminium:Bauxite(Al2O3) and Cryolite (AlF3.3NaF).

Solution 8:
Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 7

Solution 9:

Refining of metals: It is the further purification of metals obtained by reduction process to remove all the impurities.
Depending upon the nature of metal, nature of impurities and purpose for which metal is to be used. The three methods used for refining are:

  1. Liquation.
  2. Distillation.
  3. Electrolytic refining.

Solution 10:
Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 8

Solution 11:
Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 9

Solution 12:

Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 10

Solution 13:

Cryolite acts as a solvent for the electrolytic mixture in the electrolytic reduction of alumina in the Hall’s process.

Solution 14:
Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 11

Solution 15:
Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 12

Solution 16:
An alloy is a homogeneous mixture of two or more metals fused together and then solidified.
Alloys are made because they have many salient features:

  1. Tensile strength.
  2. Strength.
  3. Electrical hardness.

Solution 17:
The properties of alloys which are different from constituent metals are:

  1. Alloys are stronger and harder than the metals of which they are made.
  2. Alloys are more resistant to corrosion.

Solution 18:
Amalgam: A mixture or an alloy of mercury with a number of metals or non-metals is known as amalgams. An amalgam may be liquid such as Na/Hg or a solid like Zn/Hg.

  1. Iron does not form amalgam.
  2. Dental amalgam which is a mixture of mercury with a silver tin alloy is used for dental fillings.

Solution 19:
Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 13

Solution 20:

  1. Galvanization protects iron from rusting because in galvanization coating of zinc is done over iron articles and zinc being more electropositive would be attacked preferably than iron.
  2. Stainless steel is more useful than steel as it is harder, has high tensile strength, more lustre, more resistance to corrosion and many chemicals.
  3. Aluminium is extensively used for making aircraft parts because of features like high tensile strength, corrosion resistance light but hard and tough.
  4. Cold water has no action on aluminium while burning aluminium decomposes steam.

Solution 21:
Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 14

PAGE NO : 171
Solution 1991-1:

  1. Iron having a coating of zinc is called galvanized iron.
  2. iron which cannot be easily acted upon by acidsis called as passive iron. Galvanized iron is called passive iron since coating of zinc protects the iron from corrosion as zinc is more electropositive and so would be attacked first.

Solution 1991-2:
Zinc amalgam which is a mixture of zinc and mercury.

Solution 1992-1:
Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 15

Solution 1992-3:

  1. Nitrogen.
  2. Iodine
  3. Bromine
  4. Carbon in the form of graphite

Solution 1992-:

  1. Cryolite is Na3AlFand its chemical name is Sodium aluminium fluoride.
  2. Cryolite is used in the electrolysis of alumina. The function of cryolite is to
    • Reduce melting point of alumina
    • Make molten alumina a good conductor of electricity

Solution 1993-1:
Gold.

Solution 1993-2:
Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 16

Solution 1994-1:
Reactivity of metals with water Sodium, calcium, magnesium, iron

Solution 1994-2:
Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 17

Solution 1995-1:
Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 18

Solution 1995-2:
Zinc amalgam.

PAGE NO : 172
Solution 1996-1:
Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 19

Solution 1996-2:
Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 20

Solution 1996-3:
An alloy is a homogeneous mixture of two or more metals fused together and then solidified.

  1. The special property of duralumin is:
    • Light but hard
    • Resistant to corrosion
    • Ductile
  2. Type metal = Hard

Solution 1997-1:
Chromium and nickel is added to steel to make it stainless steel.

Solution 1997-2:
Ore: Those minerals from which a metal can be extracted profitably are called ores. For example bauxite ore is used to extract aluminium metal, hematite ore is used to extract iron metal.

Solution 1998-1:

  1. good, poor.
  2. non-malleable.
  3. form negative ions.
  4.  basic oxides.

Solution 1998-2:

  1. Mercury.
  2. Graphite.

Solution 1998-3:
Metals have 1, 2, 3 valence electrons while non-metals have 4, 5, 6 or 7 valence electrons.

Solution 1999-1:
Magnesium oxide, iron (II) oxide, lead (II) oxide and then copper (II) oxide.

Solution 1999-2:
Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 21

Solution 1999-3:

PAGE NO : 173
Solution 2000-1:

  1. Blue
  2. Red
  3. Hydrogen
  4. acidic, acidic
  5. graphite.

Solution 2001-1:

  1. Copper
  2. Iron
  3. Zinc
  4. Magnesium

Solution 2001-2:
Sodium > magnesium > Zinc > Iron > Copper

Solution 2002-1:
Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 22

Solution 2002-2:
Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 23

Solution 2003-1:
Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 24

Solution 2004-1:
Iodine is a non- metal that has a metallic luster and sublimes on heating.

Solution 2004-2:
Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 25

Solution 2004-3:
Zinc blende (ZnS)

Solution 2004-4:
Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 26

Solution 2004-5:
Galvanization.

Solution 2004-6:
Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 27

Solution 2005-1:

  1. (i) B, D F
    (ii) A, C E
  2. (i) Sodium hydroxide solution
    (ii) Cryolite
  3. Na3AlF6

PAGE NO : 175
Solution 2005-2:

  1. For stainless steel: iron, chromium
  2. For brass: Copper and zinc.

Solution 2006-1:

  1. Mercury.
  2. Cryolite.
  3. Roasting.
  4. Calcium silicate.
  5. Zone of heat absorption.

Solution 2007-1:
Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 28

Solution 2008-1:
(b)

PAGE NO : 176
Solution 2009-1:

  1. Carbon as it forms very large number of compounds while the rest do not.
  2. Mercury as it is a liquid metal while the rest aresolid.

Solution 2009-2:

  1. Copper reacts with concentrated nitric acid to produce nitrogen dioxide.
  2. Bauxite is the chief ore of aluminium.

Solution 2009-3:

  1. A is cathode and B is anode.
  2. Molten fluorides of Al, Na and Ba.
  3. Graphite rods.

Solution 2009-4:
Frank ICSE Solutions for Class 10 Chemistry - Metallurgy 29

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Frank ICSE Solutions for Class 9 Chemistry – Atmospheric Pollution

Frank ICSE Solutions for Class 9 Chemistry – Atmospheric Pollution

PAGE NO :158
Solution 1:
Acid rain is the rain that has an excessive amount of acid in it than that of normal. Two air pollutants that cause acid rain are-

    1. Oxides of nitrogen
  1. Oxides of sulphur

Solution 2:
Acid rain is responsible for retarding forest’s growth and other vegetation. Acid rain makes the soil acidic and adversely affects the plants.

Solution 3:
70% of acid rain is due to sulphur dioxide. Oxides of sulphur and nitrogen released into atmosphere from number of sources.These oxides of nitrogen gets converted into nitrogen dioxide(NO2) which reacts with water to form nitric acid.Similarly, sulphur dioxide reacts with atmospheric oxygen to form sulphur trioxide which with water forms sulphuric acid.These come down on earth as acid rain.

Solution 4:
Acid rain can be reducd by-

  1. There should be reduction in fossil fuel combustion.
  2. Use of alternate cleaner energy sources should be encouraged. Eg-nuclear power, hydro power, wind energy, solar energy etc.
  3. Air filters and scrubbers are fitted in tall industrial chimneys to control air pollution.
  4. Catalytic converters in vehicle reduce nitrogen oxide emissions from automobiles.

Solution 5:

Acid rain cause extensive damage to the environment.

  1. Vegetation – The acid rain makes the soil acidic. This adversely affects the plants and animals. This damages leaves of plants and trees. This is responsible for retarding forests and other vegetation.
  2. Fertility of soil – The activity of symbiotic nitrogen fixing bacteria present in the nodules of leguminous family is inhibited. This is responsible for destroying or reducing the fertility of the soil.
  3. Water bodies – Acid rain renders the river, lakes or even ocean water acidic, there by adversely affecting marine animals. Changes in pH affect the reproduction and survival of many species of fish and other animals.
  4. Buildings and monuments – Acid rain cause extensive damage to the buildings and monuments made from marbles, limestone, slate and mortar.
    Frank ICSE Solutions for Class 9 Chemistry - Atmospheric Pollution 1
  5. Ecological balance – Acid rain is responsible for wiping out many bacterial and blue green algae, so disrupting the whole ecological balance.
  6. Human health – Acid rain has been found to be dangerous to human health. Acidic conditions can affect human nervous, respiratory and digestive systems.

Solution 6:
Air pollution is a harmful change in the natural air quality. It includes all physical, chemical and biological agents that modify the natural characteristics of the atmosphere.

Solution 7:
Ozone is an allotrope of oxygen. It has three oxygen atoms and its molecular formula is O3.It is an unstable blue gas having pungent odour found in troposphere. It is used as a powerful oxidant, bleach and water purifier.

Solution 8:
The gases causing ozone depletion are-

  1. Chlorofluoro carbons(CFCs or freons)
  2. Methane
  3. Nitrous oxides
  4. Carbon tetrachloride
  5. Methyl bromide(a soil fumigant and insecticide)
  6. Aircraft emission
  7. n-propyl bromide and Halon-1202

Solution 9:
Greenhouse gases are-

  1. Water vapour(H2O)
  2. Carbon dioxide(CO2)
  3. Methane(CH4)
  4. Oxides of nitrogen(NOx)

Solution 10:
Frank ICSE Solutions for Class 9 Chemistry - Atmospheric Pollution 2

Solution 11:
Greenhouse effect means the progressive warming up of the earth’s surface due to the blanketing effect of man made carbon dioxide in the atmosphere. Greenhouse is a glasshouse with plants inside and  which allows short wave, incoming solar radiation to come in but does not allow the long wave,i.e. outgoing  infrared radiation to escape from inside the structure. Some of the gases in the earth’s atmosphere act like the glass in a greenhouse.They trap sun’s heat and keep the surface of the earth warm. Carbon dioxide and water vapour act as a greenhouse.

Solution 12:
Global warming is rise in the average global earth temperature . An increase in the average temperature of the earth’s atmosphere due to greenhouse effect  which can have far reaching effects on the climate and consequently on the key life, support systems of the planet, and this phenomenon is called global warming.

Solution 13:
Frank ICSE Solutions for Class 9 Chemistry - Atmospheric Pollution 3f

Solution 14:

  1. The warmer climate is changing the patterns of rainfall and snowfall.
  2. It causes increase in the frequency and severity of drought and flood also.
  3. It  is affecting our resources like water,forests  and different ecological systems.
  4. It also cause frequent natural disasters like cyclones, storms and hurricanes,floods and droughts.
  5. The global warming is damaging various ecosystems like mangrove-swamps , coral reefs and coastal lagoons, etc. due to various reasons like reduction in pH of oceanic water and increasing deposits of acids.
  6. It is damaging the world biodiversity. Vast varieties of birds, reptiles, insects, bacteria, fungi, rodents etc.have vanished out due to these effects.

Solution 15:
It has been found that in every southern spring(September-October) 50-95 %  of stratospheric ozone is destroyed at a height of 15-24 kms above ‘Antarctica’ creating pockets which have been described as ozone hole.

Solution 16:
The adverse effects of ozone layer depletion are-

  1. UV radiation causes sun-eye diseases (cataract), skin diseases, skin cancer and damage to immune system in our body.
  2. It damages plants and causes reduction in crop productivity.
  3. It damages embryos of fish, shrimps, crabs and amphibians.
  4. UV radiation damage fabrics, pipes, paints and other non-living materials on this earth.
  5. It contributes in the global warming. If the ozone depletion continues, the temperature around the world may rise at faster rate and to a large extent.

Solution 17:
Natural greenhouse effect is a process of thermal blanketing of the earth which maintains its temperature to sustain life on it. Without greenhouse effect, the climate of the earth would be too cold for most of the life to survive.

Solution 18:
The effect of warming and insulation of the earth caused due to some heat trapping gases accumulated in the atmosphere after their emission from the earth surface is called as greenhouse effect. Due to this there is rise in the average global earth temperature called global warming.

Solution 19:
When an ozone molecule is hit by UV wavelengths, it absorbs the radiant energy and photo dissociates into O2 and O giving off heat. Thus, keeps the UV radiation from reaching the earth’s surface and also causes a temperature inversion in the stratosphere that helps to maintain relatively stable climatic conditions on and near the ground.

Solution 20:
When an ozone molecule is hit by UV wavelengths, it absorbs the radiant energy and photo dissociates into O2 and O giving off heat. Thus, keeps the UV radiation from reaching the earth’s surface and also causes a temperature inversion in the stratosphere that helps to maintain relatively stable climatic conditions on and near the ground.

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