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Selina ICSE Solutions for Class 10 Maths – Geometric Progression

September 12, 2017 by veerendra Leave a Comment

Selina ICSE Solutions for Class 10 Maths – Geometric Progression

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Selina ICSE Solutions for Class 10 Maths Chapter 11 Geometric Progression

Exercise 11(A)

Solution 1(i).
selina-icse-solutions-class-10-maths-geometric-progression-11-1-i

Solution 1(ii).
selina-icse-solutions-class-10-maths-geometric-progression-11-1-ii

Solution 1(iii).
selina-icse-solutions-class-10-maths-geometric-progression-11-1-iii

Solution 2.
selina-icse-solutions-class-10-maths-geometric-progression-11-2

Solution 3.
selina-icse-solutions-class-10-maths-geometric-progression-11-3

Solution 4.
selina-icse-solutions-class-10-maths-geometric-progression-11-4

Solution 5.
selina-icse-solutions-class-10-maths-geometric-progression-11-5

Solution 6.
selina-icse-solutions-class-10-maths-geometric-progression-11-6

Solution 7.
selina-icse-solutions-class-10-maths-geometric-progression-11-7

Solution 8.
selina-icse-solutions-class-10-maths-geometric-progression-11-8

Solution 9.
selina-icse-solutions-class-10-maths-geometric-progression-11-9

Solution 10.
selina-icse-solutions-class-10-maths-geometric-progression-11-10

Solution 11.
selina-icse-solutions-class-10-maths-geometric-progression-11-11

Solution 12.
selina-icse-solutions-class-10-maths-geometric-progression-11-12

Exercise 11(B)

Solution 1.
selina-icse-solutions-class-10-maths-geometric-progression-11b-1

Solution 2.
selina-icse-solutions-class-10-maths-geometric-progression-11b-2

Solution 3.
selina-icse-solutions-class-10-maths-geometric-progression-11b-3

Solution 4.
selina-icse-solutions-class-10-maths-geometric-progression-11b-4

Solution 5.
selina-icse-solutions-class-10-maths-geometric-progression-11b-5

Solution 6.
selina-icse-solutions-class-10-maths-geometric-progression-11b-6

Solution 7.
selina-icse-solutions-class-10-maths-geometric-progression-11b-7

Solution 8.
selina-icse-solutions-class-10-maths-geometric-progression-11b-8

Solution 9.
selina-icse-solutions-class-10-maths-geometric-progression-11b-9

Solution 10.
selina-icse-solutions-class-10-maths-geometric-progression-11b-10

Exercise 11(C)

Solution 1.
selina-icse-solutions-class-10-maths-geometric-progression-11c-1

Solution 2.
selina-icse-solutions-class-10-maths-geometric-progression-11c-2

Solution 3.
selina-icse-solutions-class-10-maths-geometric-progression-11c-3

Solution 4.
selina-icse-solutions-class-10-maths-geometric-progression-11c-4

Solution 5.
selina-icse-solutions-class-10-maths-geometric-progression-11c-5

Solution 6.
selina-icse-solutions-class-10-maths-geometric-progression-11c-6

Solution 7.
selina-icse-solutions-class-10-maths-geometric-progression-11c-7

Solution 8.
selina-icse-solutions-class-10-maths-geometric-progression-11c-8

Exercise 11(D)

Solution 1(i).
selina-icse-solutions-class-10-maths-geometric-progression-11d-1i

Solution 1(ii).
selina-icse-solutions-class-10-maths-geometric-progression-11d-1ii

Solution 2.
selina-icse-solutions-class-10-maths-geometric-progression-11d-2

Solution 3.
selina-icse-solutions-class-10-maths-geometric-progression-11d-3

Solution 4.
selina-icse-solutions-class-10-maths-geometric-progression-11d-4

Solution 5(i).
selina-icse-solutions-class-10-maths-geometric-progression-11d-5i

Solution 5(ii).
selina-icse-solutions-class-10-maths-geometric-progression-11d-5ii

Solution 6.
selina-icse-solutions-class-10-maths-geometric-progression-11d-6

Solution 7.
selina-icse-solutions-class-10-maths-geometric-progression-11d-7

Exercise 11(E)

Solution 1(i).
selina-icse-solutions-class-10-maths-geometric-progression-11e-1i

Solution 1(ii).
selina-icse-solutions-class-10-maths-geometric-progression-11e-1ii

Solution 1(iii).
selina-icse-solutions-class-10-maths-geometric-progression-11e-1iii

Solution 1(iv).
selina-icse-solutions-class-10-maths-geometric-progression-11e-1iv

Solution 1(v).
selina-icse-solutions-class-10-maths-geometric-progression-11e-1v

Solution 1(vi).
selina-icse-solutions-class-10-maths-geometric-progression-11e-1vi

Solution 2.
selina-icse-solutions-class-10-maths-geometric-progression-11e-2

Solution 3.
selina-icse-solutions-class-10-maths-geometric-progression-11e-3

Solution 4.
selina-icse-solutions-class-10-maths-geometric-progression-11e-4

Solution 5.
selina-icse-solutions-class-10-maths-geometric-progression-11e-5

Solution 6.
selina-icse-solutions-class-10-maths-geometric-progression-11e-6

Solution 7.
selina-icse-solutions-class-10-maths-geometric-progression-11e-7

Solution 8.
selina-icse-solutions-class-10-maths-geometric-progression-11e-8

Solution 9.
selina-icse-solutions-class-10-maths-geometric-progression-11e-9

Solution 10(i).
selina-icse-solutions-class-10-maths-geometric-progression-11e-10i

Solution 10(ii).
selina-icse-solutions-class-10-maths-geometric-progression-11e-10ii

Solution 10(iii).
selina-icse-solutions-class-10-maths-geometric-progression-11e-10iii

Solution 10(iv).
selina-icse-solutions-class-10-maths-geometric-progression-11e-10iv

Solution 11.
selina-icse-solutions-class-10-maths-geometric-progression-11e-11

Solution 12.
selina-icse-solutions-class-10-maths-geometric-progression-11e-12

Exercise 11(F)

Solution 1(i).
selina-icse-solutions-class-10-maths-geometric-progression-11f-1

Solution 1(ii).
selina-icse-solutions-class-10-maths-geometric-progression-11f-1ii

Solution 1(iii).
selina-icse-solutions-class-10-maths-geometric-progression-11f-1iii

Solution 1(iv).
selina-icse-solutions-class-10-maths-geometric-progression-11f-1iv

Solution 1(v).
selina-icse-solutions-class-10-maths-geometric-progression-11f-1v

Solution 2.
selina-icse-solutions-class-10-maths-geometric-progression-11f-2

Solution 3(i).
selina-icse-solutions-class-10-maths-geometric-progression-11f-3i

Solution 3(ii).
selina-icse-solutions-class-10-maths-geometric-progression-11f-3ii

Solution 3(iii).
selina-icse-solutions-class-10-maths-geometric-progression-11f-3iii

Solution 3(iv).
selina-icse-solutions-class-10-maths-geometric-progression-11f-3iv

Solution 3(v).
selina-icse-solutions-class-10-maths-geometric-progression-11f-3v

Solution 4.
selina-icse-solutions-class-10-maths-geometric-progression-11f-4

Exercise 11(G)

Solution 1(i).
selina-icse-solutions-class-10-maths-geometric-progression-11g-1i

Solution 1(ii).
selina-icse-solutions-class-10-maths-geometric-progression-11g-1ii

Solution 1(iii).

Solution 2.
selina-icse-solutions-class-10-maths-geometric-progression-11g-2

Solution 3(i).
selina-icse-solutions-class-10-maths-geometric-progression-11g-3i

Solution 3(ii).
selina-icse-solutions-class-10-maths-geometric-progression-11g-3ii

Solution 3(iii).
selina-icse-solutions-class-10-maths-geometric-progression-11g-3iii

Solution 4.
selina-icse-solutions-class-10-maths-geometric-progression-11g-4

Solution 5.
selina-icse-solutions-class-10-maths-geometric-progression-11g-5

Solution 6.
selina-icse-solutions-class-10-maths-geometric-progression-11g-6

Solution 7.
selina-icse-solutions-class-10-maths-geometric-progression-11g-7

Solution 8.
selina-icse-solutions-class-10-maths-geometric-progression-11g-8

Solution 9.
selina-icse-solutions-class-10-maths-geometric-progression-11g-9

Solution 10.
selina-icse-solutions-class-10-maths-geometric-progression-11g-10

Selina ICSE Solutions for Class 9 Chemistry – Atmospheric Pollution

July 29, 2017 by veerendra Leave a Comment

Selina ICSE Solutions for Class 9 Chemistry – Atmospheric Pollution

Download Formulae Handbook For ICSE Class 9 and 10

Selina ICSE Solutions for Class 9 Chemistry Chapter 10 Atmospheric Pollution

Exercise 10

Solution 1.

The toxic substances that have an undesirable impact on different components of the environment and are injurious to life and property are known as pollutants.

Solution 2.

Effect of Pollutant on living beings:

Fluorides: Effects teeth and bones.
Smoke Particles: Cause asthma and lung diseases.
Lead: Damages the nervous and digestive systems and can cause cancer .
Mercury compounds: They cause disease like Minamata commonly found in fishermen.
Smog: It reduces visibility and induces respiratory troubles.
Nitrogen Oxide: Causes death of many plants.

Solution 3.

Air pollution: It is defined as the presence of a contaminant in the atmosphere in a concentration large enough to injure human, plant and animal life.

Air pollution takes place due to the presence of gaseous pollutants like oxides of sulphur, hydrocarbons, smoke, oxides of carbon, oxides of nitrogen, dust, particulate pollutants like mist, spray and fume.

Solution 4.

Components of air is:

Pure Air components	By Volume percentage	Concentration parts per million (ppm)
Nitrogen	78.09	780,900
Oxgyen	20.94	209,400
Inert Gases Argon	0.93	9300
Neon		18
Helium		5
Krypton		1
Xenon		1
Carbon-dioxide	0.03	315
Methane		1
Hydrogen		0.5
Natural pollutants Oxides of nitrogen Ozone		0.52 0.02

Solution 5.

Particulate Pollutant are dust, smoke, mist, spray and fume.

Solution 6.

Cigarette smoking is harmful not only for one who is smoking but also for sitting nearby and so one should avoid it. Tobacco smoke causes lung cancer and asthma.

Solution 7.

Smog: A smog is a pollutant which is a combination of oxides of sulphur and nitrogen, partially oxidized hydrocarbons and their derivatives produced by industries and automobiles from a dark, thick dust and soot laden fog known as smog.

Damaging Effect: Smog is noxious and irritating. It reduces visibility, induce respiratory troubles and can cause death by suffocation.
Photochemical Smog damages the tissues of certain plants and even decreases the yield of citrus fruits and grapes.

Solution 8.

ppm means parts per million. That is, share in 10, 00000.

Solution 9.

Major air pollutants are: Large amounts of Carbon monoxide, Sulphur dioxide, H₂S, Chlorine, HCl, Hydrocarbons and particulates. Particulate matter like sand, dust etc. Secondary pollutant like (PAN) peroxyaryl.

Solution 10.

Control of: (i) Carbon monoxide, CO emission:
Emission of CO can be controlled by :

Switching over from internal combustion engine to electrically powered cars. (b) Using alcohols, CNG, LNG in place of gasoline.
By using Catalytic Mufflers or Convertors.
Using pollution control devices to burn gasoline completely.
Using lead free petrol.

(ii) (SOx) oxides of Sulphur emission: Oxides of sulphur (SO, SO) emission can be reduced by- (a) Using coal or oil that has low sulphur content. (b) By using Scrubber, a device that absorbs gaseous pollutants.

Solution 11.

Acid rain

Factories in big cities release nitrogen dioxide and sulphur dioxide as their wastes. These gases dissolve in rainwater during rains and form nitrous acid and sulphurous acid. As the rain falls, these acids come down to the ground as an acid rain.

The normal rain is slightly acidic having a pH about 56 as carbon dioxide gas reacts with it to form a weak carbonic acid.
CO₂ + H₂O → H₂CO₃(Carbonic acid)

The pH of acid rain ranges between 56 – 35 and in some cases pH can go even lower than 2.
The two forms of deposition of acid rains are:

Dry deposits-Particles containing sulphates and nitrates
Wet deposits-dew, rain, fog, smoke

Formation of acid rain

Acid rain refers to rain which has pH less than 5.6. It is mainly caused by atmospheric pollutants.
Natural sources: Bacterial decomposition, forest fires, volcanic eruptions.
Man made sources: Industries and smelting plants, automobile exhausts, power plants etc.
Oxides of nitrogen and sulphur interact with water vapour in presence of sunlight in the atmosphere to form nitric acid and sulphuric acid mist respectively. This mist remains as vapours at high temperatures and condenses at low temperatures. These acids mix with rain (snow or fog) and fall down on the Earth resulting in acid rain.

Causes of acid rain

The formation of mineral acids like carbonic acid, nitric acid and sulphuric acid is the main cause of acid rain.

Formation of Nitric acid and Nitrous acid

Nitrogen and oxygen (that is oxides of nitrogen) combines in the presence of thunder and lightning to form nitric acid.
They are also produced by internal combustion engines (automobile engines). This then gets oxidized in the atmosphere to nitrogen dioxide. Nitrogen dioxide combines with water to form a mixture of nitrous acid and nitric acid.

N₂ + O₂ → 2NO
(Nitrogen oxide)

2NO + O₂ → 2NO₂(Nitrogen dioxide)

2NO₂ + H₂O → HNO₂ + HNO₃(Nitrous acid) (Nitric acid)

Formation of Sulphuric acid and Sulphurous acid

Impurities in the coal: Coal used in power plants contains upto 4% sulphur. On combustion it forms pollutant sulphur dioxide (i.e, oxides of sulphur).
S + O₂ → SO₂(Sulphur dioxide)

Sulphur dioxide reacts with water vapour to form sulphurous acid.
SO₂+ H₂O → H₂SO₃(Sulphurous acid)

Sulphur dioxide can also be oxidized to sulphur trioxide.
2SO₂ + O₂ → 2SO₃(Sulphur trioxide)

Sulphur trioxide reacts with water vapour to form sulphuric acid.
SO₃ + H₂O H₂SO₄(Sulphuric acid)

Impact of Acid rain

Changes the acidity of soil: The acids present in the acid rain like, nitric acid, nitrous acid and sulphuric acid, sulphurous acid increases the acidity of soil. It removes calcium and potassium minerals i.e., basic ingredients from the soil losing their fertility.

The hydrogen ions H⁺ which are added to the soil, when acid rain falls on the Earth interact chemically with existing soil minerals.

Affects water bodies and marine organisms: The water of lakes and rivers is becoming acidic, which may no longer support aquatic life.

Material damage: It increases corrosion of metals, disintegrates paper and leather. Weakens building materials such as statues, marbles, sculptures, limestone, slate, mortar etc. These materials become pitted and weakened mechanically. The Taj Mahal in India faces this problem.
CaCO₃ + H₂SO₄ → CaSO₄ + CO₂ + H₂O
CaCO₃ + 2HNO₃→ Ca(NO₃)₂ + CO₂ + H₂O

Impact on living things: It damages forests. Acid rain gets absorbed by plants, animals directly or indirectly toxicity enters food chain affecting humans. They can affect a person’s breathing, at sufficiently high concentrations. Sulphur dioxide irritates the upper respiratory tract, which serve to expel soot particles and dust in the inhaled air. At even lower concentrations, it does still greater harm by injuring lung tissues.

Solution 12.

Sulphur dioxide pollutes the air, effects the yield of crops and causes damage to lungs, SO₂ gets converted to SO₃ and combines with water drops of air and cause acid rain.

Solution 13.

In the atmosphere ozone is formed by the action of ultraviolet rays of the sun on oxygen.
3O_{2 (g)} → 2O_3(g)

The high energy UV radiations break oxygen molecules into oxygen atoms.
O₂ + Far UV → O + O
Oxygen molecule Oxygen atoms

Oxygen atom reacts with oxygen molecule to form ozone.
O + O₂ → O₃Atom Molecule Ozone

The Net reaction is:
3O₂ + Far UV → 2O₃

Solution 14.

It is formed by the action of ultraviolet rays of the Sun on oxygen.
O₃ → O + O₂

Ozone layer acts as a blanket in the atmosphere 16 km height above the Earths surface.
It absorbs harmful ultraviolet rays (UV radiations) coming from the Sun and prevents them to reach the surface of the Earth.

Ultraviolet rays have very harmful effects on living things. It causes skin cancer. It destroys many organic species which are necessary for life.

Thus it protects the life on earth from harmful effects of Ultra Violet Rays. Which can cause (a) Skin cancer (b) destroy many organic species necessary for life.

Solution 15.

Chemicals responsible for ozone destruction free radical chlorine (Cl) and nitrioxide (NO) are responsible for ozone depletion i.e. react with O₃Free radical chlorine (Cl) is produced by UV rays from chlorofluoro carbons enter the atmosphere because of excessive use as solvents, Aerosol, Spray, Propellants, Refrigerants and blowing agents for plastic foams.

Chemicals responsible for the depletion of ozone layer

Fuel of planes: Burning of fuels of planes emits large quantity of nitric oxide and other gases in the atmosphere. Nitric oxide reacts with ozone and form nitrogen dioxide and nitrogen trioxide. This causes depletion of ozone.

NO(g) + O₃(g) → NO₂(g) + O₂(g)
(Nitrogen dioxide)

NO₂(g) + O₃(g) → NO₃(g) + O₂(g)
(Nitrogen trioxide)

Excessive use of chlrofluro carbon: It is released by refrigerators and air conditioning systems.
It causes reduction of ozone layer that protects us from harmful ultraviolet rays (UV radiations) of the Sun.

The chlorofluro carbons are decomposed by the ultraviolet rays to highly reactive chlorine which is produced in the atomic form.

The free radical [Cl] reacts with ozone to form chlorine monoxide.

Cl + O₃ → ClO + O₂(Chlorine monoxide)

This causes depletion of ozone layer. Chlorine monoxide then reacts with atomic oxygen to produce more chlorine free radicals.

ClO + O → Cl + O₂(Free radical)
Again this free radical destroys ozone and the process continues giving rise to depletion of ozone layer.

Selina ICSE Solutions for Class 9 Chemistry – Study of the First Element – hydrogen

July 29, 2017 by veerendra Leave a Comment

Selina ICSE Solutions for Class 9 Chemistry – Study of the First Element – hydrogen

Download Formulae Handbook For ICSE Class 9 and 10

Selina ICSE Solutions for Class 9 Chemistry Chapter 9 Study of the First Element – hydrogen

Exercise 9

Solution 1.

(a) The position of hydrogen in the periodic table
selina-icse-solutions-class-9-chemistry-study-first-element-hydrogen-1
Hydrogen is first element in the periodic table. It has an atomic number l and an atomic mass of 1.00794 amu, occupying group – IA. Its position is peculiar because it is grouped with metals although it is a non-metal properties. Hydrogen relate to Group IA as well as Group VII A.

(b) The properties of hydrogen resemble the properties of Group IA elements (Alkali metals), and some of it resembles the properties of Halogens (VIIA), so Hydrogen was put at the top of the periodic table so that the symmetry of the modern periodic table is not disturbed.

All elements in Group- IA have one electron in outermost shell, so they havevalency one.
These elements in Group-IA are good reducing agents.
All elements of this group formsoxide which are highly basic and dissolves in water to form strong alkalis.
They impartcolour to a flame.

Solution 2.

Similarity of hydrogen with alkali metals and halogens

	Similarity of hydrogen with alkali metals [Group 1 (IA)]	Similarity of hydrogen with halogens [Group 17 (VIIA)]
Electronic configuration	Electronic configuration = 1. Thus, 1electro in the outermost valence shell. Example: H=1; Li=2, 1; Na=2,8,1; K=2,8,8,1	One electron less than the nearest noble gas. Example: H= 1 (He=2) F= 2,7 (Ne=2,8) Cl= 2,8,7 (Ar=2,8,8)
Ion formation	Electropositive character exhibited. H 1e^– → H¹⁺Li 1e^– → Li¹⁺Na 1e^– → Na¹⁺	Electronegative character exhibited. H + 1e^– → H^1-F + 1e^– → F^1-Cl + 1e^– → Cl^1-
Valency	Electrovalency of one exhibited. H¹⁺ , Li¹⁺, Na¹⁺	Electrovalency and covalencyexhibited. Hydrogen: forms NaH (electrovalent)forms CH₄(covalent) Chlorine: forms NaCl (electrovalent) forms CCl₄ (covalent)
Reactions	Strong affinity for non-metals (example: O, S, Cl) Hydrogen: forms H₂O; H₂S; HCl Sodium: forms Na₂O; Na₂S; NaCl	__
Reducing agent	Acts as a reducing agent. Hydrogen: CuO + H₂ → Cu + H₂O Sodium: CuO + 2Na → Cu + Na₂O	__
Atomicity	__	Diatomic molecules are formed. (Two atoms linked by a single bond) Hydrogen H:H or H-H → H₂ Chlorine Cl:Cl or Cl-Cl → Cl₂

Resemblance with Halogens:

Both exist in the form of diatomic molecules.
Both show gaseous nature.
Both have a valency of 1.
Both are non-metals.
Both lose electron to term anions.

Solution 3.

(a) Hydrogen is found in minute traces in the Earth’s crust and the Earth’s atmosphere. The atmosphere around the sun and stars is found to contain 1.1 % hydrogen.

(b) Henry Cavendish when prepared this gas from iron and dil. acids, he established its elementary nature and showed that when the gas burns in air, water is formed. It was on account of this property that Lavoisier in 1783 named it hydrogen (Greek word meaning water-former).

Solution 4.

(a) A monovalent metal
2Na + H₂ → 2NaH
(Sodium hydride)

(b) A divalent metal
Ca + H₂ → CaH₂(Calcium hydride)

Solution 5.

(a) Calcium: is not used in lab preparation of hydrogen because:

The reaction and very violent and exothermic hence dangerous.
The heat liberated ignites the hydrogen.
Calcium is expensive.

(b) Iron: Iron reacts slowly at ordinary temperatures, hence requires heating. The hydrogen produced also contain impurities like sulphur dioxide and hydrogen sulphide. Hence, it is not used in lab preparation of hydrogen.

(c) Aluminium: It is not used in the lab preparation of hydrogen because oxides of this metal keep sticking to the surface of the metal. Thus the steam does not come in contact with metal and hence reaction stops. .

(d) Sodium: It is riot used in the lab preparation of hydrogen because the reaction is violent. The sodium melts into a globule and darts about freely on the surface of water hence the collection of hydrogen is difficult.

Solution 6.

Depending upon the nature of reaction taking place between metals and substances like air, water and acids, metals are arranged in a vertical series in order of their activity. Such a series is called activity series of metals.

The metals places near the top of the series are the most reactive, while those placed near the bottom are the least reactive.

When dilute hydrochloric acid or dilute sulphuric acid react with the metals above hydrogen in the activity series, they produce hydrogen. But the metals below hydrogen in the activity series do not.

Solution 7.

(a) Reactants: Nitrogen and hydrogen (Haber process)

Chemical equation:
selina-icse-solutions-class-9-chemistry-study-first-element-hydrogen-7-1

Observation and conditions
Three volumes of hydrogen and one volume of nitrogen react at temperature 450^oC-500^oC at the pressure of 200-900 atm, in presence of a finely divided iron which acts as a catalyst, and promoter molybdenum.

(b) Reactants: Chlorine and hydrogen

Chemical equation:
selina-icse-solutions-class-9-chemistry-study-first-element-hydrogen-7-2

Observation and conditions
Hydrogen and chlorine (in their equal volumes) react slowly in diffused sunlight but reacts explosively in direct sunlight. A spontaneous reaction takes place with the release of a large amount of energy.

Chemical equation:
H₂ + S → H₂S

Observation and conditions
Hydrogen gas when passed through molten sulphur, it reacts to give another gas, hydrogen sulphide.

(d) Reactants: Oxygen and hydrogen

Chemical equation:
2H₂ + O₂ → 2H₂O

Observation and conditions
Hydrogen burns with a pop sound in oxygen. It burns with a pale blue flame forming water.

Solution 8.

(a) Among the given metals Zinc is most suitable.
(i) Copper: In case of copper, It is placed below hydrogen in the activity series. So it does not displace hydrogen from acid.
Cu + HCl → No reaction
(ii) In case of Mg; it is a very expensive metal.
(iii) In case of sodium, it reacts with explosively and violently.

(b) Among the given acids we prefer dilute sulphuric acid.
We reject concentrated sulphuric, dilute nitric and concentrated nitric acid because these are powerful oxidising agents and oxygen formed due to its decomposition oxidises the hydrogen to water.

(c) Modification: Collect the gas by downward displacement of water when all the air from the apparatus has been expelled. Drying Agent used is Calcium Chloride.

Solution 9.

(a) Iron reacts reversibly with steam. Hence the hydrogen formed is removed as it is released to prevent reduction of triferric tetraoxide.
Fe + 4H₂O → Fe₃O₄ + 4H₂ ?
(Steam)

(b)
selina-icse-solutions-class-9-chemistry-study-first-element-hydrogen-9

Solution 10.

(a) The metal is magnesium
(b) Mg + H₂O → MgO + H₂

Solution 11.

(a) Substance A is CuO and substance B is Cu.

(b) Test for water
(i) It is neutral to litmus
(ii) It changes anhydrous copper sulphate into blue salt.

(c) When substance A i.e, CuO reacts with hydrogen, it removes oxygen and we get free metal i.e. Cu.

(d) CuO + H₂ → Cu + H₂O

(e) No, there is no reaction between substance B and dilute hydrochloric acid because copper does not displace hydrogen from acids.

(f) Cu + HCl → No reaction

Solution 12.

Magnesium lies above Hydrogen in reactivity series and can displace hydrogen from acid whereas, Mercury and silver lie below hydrogen in reactivity series and cannot displace hydrogen from acid and hence nothing happens.

Solution 13.

Soap bubbles containing hydrogen rapidly rise up in air as hydrogen is lighter than air.

Solution 14.

Bosch Process
Bosch process consists of following steps.

Step 1 :

Steam is passed over a hot coke (at 1000^oC) in a special type of a furnaces called converters.
In this step carbon reacts with water to form carbon monoxide and hydrogen gas. This mixture is called water gas. selina-icse-solutions-class-9-chemistry-study-first-element-hydrogen-14-1

Step 2 :

In this step excess of steam is mixed with water gas and entire mixture is passed over heated ferric oxide and chromic oxide. Ferric oxide acts as catalyst and chromic oxide as promoter.
selina-icse-solutions-class-9-chemistry-study-first-element-hydrogen-14-2

Step 3 :

In this step removal of carbon dioxide from reaction mixture takes place. The mixture of carbon dioxide and hydrogen is forced through cold water under pressure at 30 atmospheric pressure or through caustic potash solution which dissolve carbon dioxide leaving behind hydrogen gas.
2KOH + CO₂ → K₂CO₃ + H₂O

Step 4 :

In this last step, mixture is passed through ammonical solution of cuprous chloride solution so as to dissolve carbon monoxide. CO is removed by bubbling the gas through ammoniacal cuprous chloride solution. The moisture is removed by cooling the gas about 20°C when water vapoursfreeze. The pure and dry hydrogen gas is collected in steel cylinders.
CuCl + CO + 2H₂O → CuCl.CO.2H₂O

Solution 15.

(a) Cold water:

Sodium metal wrapped in small piece of wire gauze or Sodium amalgamated with mercury is used. This prevents sodium from darting about.
2Na + 2H₂O → 2NaOH + H₂ ↑

(b) Hot water:

Zn or Mg can be used.
Mg + H₂O → MgO + H₂ ↑
(boiling water)

(C) Steam:

Iron reacts with the steam and the reaction is reversible. Iron reacts with steam when it is red hot as hydrogen is blown out of contact with iron by the force of current of the steam.
selina-icse-solutions-class-9-chemistry-study-first-element-hydrogen-15

Solution 16.

Metals

Mg, Al, Zn, Fe do not react with cold water. It reacts with boiling water liberating hydrogen gas but the reaction is very slow.
Mg, Al, Zn, Fe react with the hot steam in the heated state and form the corresponding oxide and hydrogen gas.
Iron reacts with the steam and the reaction is reversible.

Magnesium
Reaction of boiling water with steam is slow but Mg liberates Hydrogen rapidly with steam.

Mg + H₂O → MgO + H₂ ↑
(boiling water)

Aluminium

Gets coated with Al₂O₃ on rubbing with sand paper its oxide coating is removed and then it reacts with steam to produce hydrogen.

2Al + H₂O → Al₂O₃ + 3H₂ ↑
(steam)

Zinc

Zinc reacts with steam and produce zinc oxide and H₂

Zn + H₂O → ZnO + H₂ ↑
(steam)

Iron

Iron produces H₂ when red hot the reaction is reversible but as soon as hydrogen is produced it is blown out of contact with iron by the force of the current of steam.

(steam)

Non-metals

Bosch Process (From Coke)
Bosch process consists of following steps.

Step 1 :

Step 2 :

Step 3 :

2KOH + CO₂ → K₂CO₃ + H₂O

Step 4 :

In this last step, mixture is passed through ammonical solution of cuprous chloride solution so as to dissolve carbon monoxide. CO is removed by bubbling the gas through ammoniacal cuprous chloride solution. The moisture is removed by cooling the gas about 20C when water vapoursfreeze. The pure and dry hydrogen gas is collected in steel cylinders.

CuCl + CO + 2H₂O → CuCl.CO.2H₂O

Solution 17.

(a) Zinc and iron lie above hydrogen in reactivity series and can displace hydrogen from acid.

Zn + H₂SO₄ → ZnSO₄ + H₂ ↑
(dilute)

Fe + H₂SO₄ → FeSO₄ + H₂ ↑
(dilute)

(b) Zn + 2HCl → ZnCl₂ + H₂ ↑
(dilute)

Fe + 2HCl → FeCl₂ + H₂ ↑
(dilute)

Copper lies below hydrogen. Thus, it cannot displace hydrogen from acids.

Solution 18.

Two alkalis which can displace hydrogen are NaOH and KOH.

Aluminium

2Al + 6NaOH → 2Na₃AlO₃ + 3 H₂ ↑
(Sodium aluminate)

2Al + 2KOH + 2H₂O → 2KAlO₂ + 3 H₂ ↑
(Potassium meta aluminate)

Zinc

Zn + 2NaOH → Na₂ZnO₂ + H₂ ↑
(Sodium zincate)

Zn + 2KOH → K₂ZnO₂ + H₂ ↑
(Potassium zincate)

Aluminium and Zinc have unique nature; They react with acids and can even react with hot concentrated alkalis to form hydrogen and a soluble salt. Salt s (oxides and hydroxide) of these metals are Amphoteric.

Solution 19.

(a) 2Na + 2H₂O → 2NaOH + H₂(b) Ca + 2H₂O → Ca(OH)₂+ H₂(c) Mg + H₂O → MgO + H₂(d) Zn + H₂O → ZnO + H₂(e) 3Fe + 4H₂O → Fe₃O₄ + 4H₂(f) Zn + 2HCl → ZnCl₂ + H₂(g) 2Al + 3H₂SO₄ → Al₂(SO₄)₃ + 3H₂(h) Fe + 2HCl → FeCl₂ + H₂(i) Zn + 2NaOH → Na₂ZnO₂ + H₂(j) 2Al + 2KOH + 2H₂O → 2KAlO₂ + 3H₂

Solution 20.

(a) Lead reacts with dilute sulphuric acid and hydrochloric acid and forms an insoluble coating of lead sulphate and lead chloride respectively. Hence, further reaction is prevented.

(b) When potassium and sodium react with dilute sulphuric acid, H2SO4 or dilute HCl, the reaction is highly explosive and practically not feasible.

Solution 21.

(a) Sodium hydroxide + zinc → hydrogen + Sodium zincate
(b) Calcium + water calcium → hydroxide + Hydrogen

Solution 22.

Hydrogen gas is collected by the downward displacement of water. This is because-
- It is virtually insoluble in water.
- It forms an explosive mixture with air and therefore, cannot be collected by downward displacement of air, even though it is lighter than the air.
A candle when brought near the mouth of the jar containing hydrogen gas starts burning but the candle is extinguished when pushed inside the jar because, Because hydrogen is a combustible gas but a non-supporter of combustion i.e. it burns itself but does not allow substances to burn in it.
An oxy-hydrogen flame is used for welding and cutting metals because, when a mixture, of hydrogen and oxygen is burnt, temperatures as high as 2500°C is produced. This forms the basis for its use in oxy-hydrogen flame used in cutting and welding of flames.
Apparatus for the laboratory preparation of hydrogen should be air tight and away from a naked flamebecause, mixture of hydrogen and air explodes violently when brought near a flame.

Solution 23.

(a) (iii) non-combustible
(b) (iii) a base (c) (iii) CaO
(d) (iv) It is strong oxidising agent.
(e) (iii) PbO is oxidised to Pb
(f) (ii) Zn
(g) (ii) Copper

Solution 24.

(a) CuO, H₂O
(b) sparingly
(c) amalgam
(d) iron, magnesium, aluminium
(e) above, dilute hydrochloric, dilute sulphuric.

Solution 25.

(a) Hydrogen is used as a fuel in the form of coal gas, water gas and liquid hydrogen.
(b) All metals above hydrogen in reactivity series react with acids to give hydrogen.
(c) Metals like palladium or platinum or nickel absorb hydrogen at room temperature.
(d) The reaction of hydrogen with oxygen is explosive with pop sound.
(e) Concentrated sulphuric acid reacts with zinc to liberate sulphur dioxide.

Selina ICSE Solutions for Class 9 Chemistry – The Periodic Table

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Selina ICSE Solutions for Class 9 Chemistry – The Periodic Table

Download Formulae Handbook For ICSE Class 9 and 10

Selina ICSE Solutions for Class 9 Chemistry Chapter 8 The Periodic Table

Exercise 8

Solution 1.

(a) In 1913, Mosley made an important discovery of atomic number. Thus, he gave the modern periodic law that states that, The physical and the chemical properties of elements are the periodic functions of their atomic numbers.
(b) Eighteen groups and seven periods.

Solution 2.

Last elements of each period have outer most shell complete i.e. 2 or 8 electrons.
Name is Inert-gases or Noble gases.

Solution 3.

(a) A group: Vertical columns in a periodic table which have same-number of valence electrons, and similar chemical properties are called a group.
(b) A period: In a periodic table elements are arranged in the order of increasing atomic numbers in horizontal rows called periods.

Solution 4.

Atomic number can determine that which element will be the first and which is the last in a period of the periodic table.

Solution 5.

(a) Group I A elements: Lithium, Sodium.
(b) Group 17 element: Fluorine, Chlorine
(c) Group 18 (zero group elements) : Helium; Neon

Solution 6.

(a) Group IA is known as Alkali Metals group.
(b) Group 17 is known as Halogens group. (c) Group 18 is known as Transition elements.

Solution 7.

(a) Number of elements in 1st period of the modem periodic table – 2 (two) (b) Number of elements in 3rd period of the modem periodic table – 8 (eight)

Solution 8.

(a) Increases
(b) Increases

Solution 9.

The valency of elements increases from 1 to 4 upto the element carbon(C), and then falls to 1 upto the element fluorine (F) and Neon (Ne) Zero.

Solution 10.

(a) periods
(b) increases
(c) decreases

Solution 11.

In a period, the size of an atom decreases from left to right. This is because the nuclear charge increases from left to right in the same period, thereby bringing the outermost shell closer to the nucleus.
Thus, in a particular period, the alkali atoms have the largest size and the halogen atoms are the smallest.
selina-icse-solutions-class-9-chemistry-periodic-table-11

Solution 12.

(a) (i) Hand P are noble gases
(ii) G and 0 are halogens
(iii) A and I are alkali metals
(iv) D and L have valency of 4.

(b) The formula of the resulting compound will be Li₂O. Because, A stands for Lithium and F stands for O and valency of Lithium is +1 and valencyof O is -2. That is, A₂ F.

Solution 13.

This is because; Na and Al have capacity to donate the electron due to which there valency is positive. Whereas Cl and K can gain or lose one electron due to which their valency is -1 and + 1 respectively. Only this is the difference between these two.

Solution 14.

(a) The greatest metallic character can be expected at the bottom of the group.
(b) The largest atomic size can be expected at the lower part of the group.

Solution 15.

No. of valence electrons remain same as we go down in a group that too on the left side of a period.

Solution 16.

(a) Magnesium is the ‘x’ element which belongs to the third period and group II of the periodic table and has atomic number 2. Therefore, the number of valence electrons are 2 (two).
(b) Valency is + 2.
(c) Alkaline earth metals.
(d) The elements is Magnesium

Solution 17.

(a) VII A
(b) Third period
(c) Seven
(d) Valency of T = -1
(e) Non – metal

Solution 18.

(a) Helium
(b) Silicon
(c) 4, 3
(d) Argon
(e) Noble gases
(f) Carbon tetrachloride (CCl₄)
(g) Silicon, Phosphorus
(h) Sodium chloride (NaCl)
(i) Li and Mg; Be and Al; B and Si
(j) Sodium
(k) Typical elements of Period 2 belonging to group 14 and 15 are carbon and nitrogen.
Typical elements of’ Period 3 belonging to group 14 to 15 are silicon and phosphorus.
(l) Beryllium

Solution 19.

Column A	Column B
(a) Elements short of 1 electron in octet	(v) Halogens
(b) Highly reactive metals	(iii) Alkali metals
(c) Unreactive elements	(ii) Noble gases
(d) Elements of groups 3 to 12	(i) Transition elements
(e) Radioactive elements	(vi) Actinides
(f) Elements with 2 electrons in outermost orbit	(iv) Alkaline earth metals

Solution 20.

Atomic No.

Element

Electronic configuration

Select element of same group

Sodium

Phosphorus

Sulphur

Fluorine

2,8,1

2,8,5

2,8,6

2,7

Solution 21.

The relative atomic mass of a light element up to calcium is approximately 20 its atomic number.

Solution 22.

Atomic number of P = 19
Electronic configuration = 2, 8, 8, 1 Group number of the element = 1 A Period number of the element = 4
P is a metal.

Selina ICSE Solutions for Class 9 Chemistry – Atomic Structure

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Selina ICSE Solutions for Class 9 Chemistry – Atomic Structure

Download Formulae Handbook For ICSE Class 9 and 10

Selina ICSE Solutions for Class 9 Chemistry Chapter 7 Atomic Structure

Exercise 7

Solution 1.

The latest research on atom has proved that most of the postulates of Dalton’s atomic theory contradict. But Dalton was right that atoms take part in chemical reactions. Comparison of Dalton’s atomic theory with Modem atomic theory.

Dalton’s atomic theory	Modern atomic theory
1. Atoms are indivisible particles.	1. Atoms are divisible into sub-atomic particles like protons, neutrons and electrons.
2. Atoms can neither be created nor destroyed.	2. Atoms can be created and destroyed by nuclear fusion and fission.
3. The atoms of an element are alike in all respect and differ from atoms of other elements.	3. The atoms of an element may not be alike in all respects, as it is seen in the case of isotopes. Isotopes which are atoms of the same element having the same atomic number but different mass numbers.

Solution 2.

(a) Inert elements: The elements which have complete outer most shell i.e. 2 or electrons. They ordinarily do not enter into any reaction.

(b) These exist as monoatoms because molecules of these elements contain only one atom.

(c) Valence electrons: The number of electrons present in the outermost shell or valence shell is known as valence electrons.

Solution 3.

The three isotopes of hydrogen differ only due to their mass number which is respectively 1,2 and 3 and named protium, deuterium and tritium.
selina-icse-solutions-class-9-chemistry-atomic-structure-3

Solution 4.

Atomic number	Name with valency
4	–
15	A solid non-metal of valency 3.
8	A gas of valency 2.
19	A metal of valency 1.
14	A non-metal of valency 4.

Solution 5.

Atom	Atomic number	Atomic mass	No. of Protons	No. of Electrons	No. of Neutrons	Electronic configuration
(a) Sodium	11	23	11	11	12	2, 8, 1
(b) Chlorine	17	35	17	17	18	2, 8, 7
(c) Oxygen	8	16	8	8	8	2, 6
(d) Carbon	6	12	6	6	6	2, 4

selina-icse-solutions-class-9-chemistry-atomic-structure-5

Solution 6.

The significance of the number of protons found in the atoms in each of different element is fixed its place in periodic table.

Solution 7.

Atomic numbers of –

X	Y	Z
6	9	12
(2,4)	(2,7)	(2,8,2)

(a) Y (2,7) forms Anion.
(b) Z (2, 8, 2) forms Cation.
(c) X (2,4) has four electrons in the valence shell.

Solution 8.

(a) X⁺¹(b) Oxidising agent, because it has ability to donate electron.

Solution 9.

(a) Mass number:The atomic mass number is defined as the sum of the number of protons and neutrons contained in the nucleus of an atom of that element. It is denoted by the symbol A.

(b) Ion: An atom or molecule that carries a positive or negative charge because of loss or gain of electrons.

(c) Cation: It is positively charged ion that is formed when an atom loses one or more electrons e.g. Na⁺, Hg²⁺, Ca²⁺ etc.

(d) Atom: It is defined as the smallest unit of matter which takes part in a chemical reaction.

(e) Element: It is a substance which cannot be split up into two or simpler substances by usual chemical methods of applying heat, light or electric energy. e.g. Hydrogen, Oxygen, Chlorine etc.

(f) Orbit: It is defined as a circular path around the nucleus in which electrons of the atom revolve.

Solution 10.

Atomic number = 2 Mass number = 4

Solution 11.

(a) (i) Atom E contains 7 protons.
(ii) Atom E has an electronic configuration 2, 7.

(b) Atom C Stands for ₇³Li
Atom D stands for ₈¹⁶O
Compound formula = Li₂O

Solution 12.

No of electrons in M Shell = 2
Number of electrons in K and L shell will be 2, 8 and respectively.
Therefore, Electronic configuration will be: 2, 8, 2.
Atomic number = 2 + 8 + 2 = 12, Since, atomic number = Number of Protons
No of Protons = 12

Solution 13.

selina-icse-solutions-class-9-chemistry-atomic-structure-13
(a) (ii) Electronic configuration = 2, 8, 2
(b) Mass numbers are different of two isotopes of magnesium because of different number of neutron, that is, 12 and 14 respectively.

Solution 14.

Nucleons: Particles which constitute nucleus are called nucleons. Proton and neutrons are the nucleons.
At. weight of phosphorus = 31 Atomic number = 15
Total number of nucleons = 31 (No. of P + No. of N) No. of neutrons = 31 – 15 = 16
Electronic configuration
No. of electrons = 15 = 2,8,5
selina-icse-solutions-class-9-chemistry-atomic-structure-14

Solution 15.

(a) Atoms of the same elements differing in the number of neutrons in their nuclei are known as isotopes. Thus, isotopes of an element have the same atomic number but different atomic mass number.
The fundamental particles is Neutrons which differs.

Uses of isotopes:

Some isotopes are Redioactive; isotopes of cobalt are used for treating cancer and other diseases.
An isotopes of uranium ²³⁵U is used as a fuel in nuclear reactor.

(b)

selina-icse-solutions-class-9-chemistry-atomic-structure-15

Solution 16.

In chemical reactions only electrons take part. The chemical properties depend upon the electronic configuration.

The isotopes of element ₁₇³⁵Cl and ₁₇³⁷Cl have same atomic number and hence, the same configuration. So they have same chemical properties. These differ only in physical contents and weights because neutrons contribute to the mass of an atom.

₁₇³⁵Cl and ₁₇³⁷Cl have different number of neutrons 18 and 20 respectively.

Solution 17.

The atomic masses of the isotopes of chlorine are 35 and 37. However in any given sample of chlorine gas, the isotopes occur in approximate 3 : 1, 75% of Cl³⁵, and 25% of Cl³⁷. Therefore, the relative atomic mass or atomic weight of chlorine is 35.5.

Fractional atomic weight of chlorine

selina-icse-solutions-class-9-chemistry-atomic-structure-17

Solution 18.

(a) Atomic number: The number of protons present in the nucleus of an atom is the atomic number of that atom. It is represented by the symbol Z.
Atomic number (Z) = Number of protons (p)

(b)

	No. of Protons	No. of Electrons	No. of Neutrons	Atomic number	Mass number
³⁵ Cl ¹⁷	17	17	18	17	35
³⁷ Cl ¹⁷	17	17	20	17	37

(c) Electronic configuration of chlorine is 2, 8, 7.

Solution 19.

(a) Hydrogen
(b) Element of zero group i.e. He (Helium)
(c) Calcium (2, 8, 8, 2). Therefore, 2 electrons in valance shell. Hence valency is 2.
(d) Chlorine atoms: ₁₇³⁵Cl and ₁₇³⁷Cl
(e) K shell.

Solution 20.

(a) Physical properties depend on the Atomic mass and isotopes have different mass number. (A) i.e. they have different number of neutrons. So, isotopes have different physical properties.

(b) Argon does not react as, Argon has completely filled outer-most orbit. The atomic number of argon is 18. Therefore, electronic configuration is 2, 8, 8. There are 8 electrons in the outermost or valance shell. Therefore, argon does not react.

(c) Actual Atomic Mass is greater than mass number (P + N) since mass number is a whole number approximation of atomic mass unit. In fact Neutrons are slightly heavier than protons and atom includes the existence of over 200 sub-atomic particles.

(d) ₁₇³⁵Cl and ₁₇³⁷Cl are isotopes of chlorine element which differ in number of neutrons. Whereas chemical properties are determined by electronic configuration of an atom. Isotopes of an element are chemically alike.

Solution 21.

Element A

Atomic number = 7
Electronic configuration: = 2, 5
Valency of element A = 8-5 = (3^–)

Element B

Electronic configuration 2,8,8 Valency of element B = Zero Element C
Number of Electrons 13 Electronic configuration: 2,8,3
Valancy of element C = 3⁺

Element D

Protons = 18 = electrons Electronic configuration: 2,8, 8
Valency of element D = Zero

Element E

Electronic configuration = 2, 8, 8, 1
Valency of element E = 1⁺[ii] C and E are metals [iii] A is a Non-metal
[iv] B and D are inert gases. (A, C and E are not inert gases.)

Solution 22.

(a) C. Atomic nucleus
(b) A. 6
(c) C. 2,8,8,1

Solution 23.

Elements tend to combine with one another to attain the stable electronic configuration of the nearest noble gas/inert gas (Duplet or Octet)

(a) Sodium Chloride

The electronic configuration of Sodium is 2, 8, Thus, Sodium atom tends to lose one electron to attain the stable electronic configuration of neon gas 2, 8.

The electronic configuration of Chlorine is 2, 8, 7. Thus, Chlorine atom needs one electron to complete its octet and achieve the stable electronic configuration of Argon 2, 8, 8.

When sodium and chlorine atoms approach each other, the sodium atom, Na, loses an electron to form sodium ion, The cation, Na⁺, carries a single positive charge.
Na → Na⁺ + e^–

The electron lost by sodium atom is transferred to the chlorine atom forming chloride ion, Cl^–.
Cl + e^– → Cl^–

The sodium and chloride ions thus, achieve stable electronic configurations.
selina-icse-solutions-class-9-chemistry-atomic-structure-23-1

(b) Hydrogen H₂

Hydrogen atom has one electron in its valence shell. Hydrogen atom needs one more electron to complete its duplet and attain the stable electronic configuration of Helium.

In case of hydrogen H₂ molecule, each of the two hydrogen H atoms contributes one electron so as to have one shared pair of electrons. Both the hydrogen atoms attain stable duplet structure resulting in the formation of a single covalent bond [H – H] between them.

Both the hydrogen atoms have equal attraction for the electrons. Thus, the shared pair of electrons remains equidistant from both the atoms.

selina-icse-solutions-class-9-chemistry-atomic-structure-23-2

Solution 24.

Element Symbol	Atomic Number	Mass Number	Number of Neutrons	Number of Electrons	Number of Protons
Li	3	6	4	3	3
Cl	17	35	18	17	17
Na	11	23	12	12	11
Al	13	27	14	13	13
S	15	32	16	15	15