Saturday, 2 May 2026

Nitrogen and Its Compounds (At a Glance)

Basic Facts About Nitrogen

i. Symbol: N

ii. Atomic Number: 7

iii. Group: 15 (Group V A)

iv. Period: 2

v. Electronic Configuration: 1s² 2s² 2p³

vi. Valency: 3 or 5

vii. Nature: Non-metal

Occurrence

* Makes up about 78% of Earth’s atmosphere as nitrogen gas (N₂) (free element)

* Found in: Proteins

(amino acids)

* Nucleic acids (DNA & RNA)

* Fertilizers (nitrates, ammonium salts)

Properties of Nitrogen Gas (N₂)

i. Colorless, odorless, tasteless gas

ii. Chemically inert due to strong triple bond (N≡N)

iii. Does not support combustion

iv. Slightly soluble in water

Important Compounds of Nitrogen

1. Ammonia (NH₃)

Prepared by: Haber Process

N2(g) + 3H2(g) → NH3(g)

Properties Ammonia

i. Pungent smell

ii. Highly soluble in water

iii. Basic in nature

Uses:

i. used for Fertilizer production

ii. As a Refrigerant

iii. For the Manufacture of nitric acid

2. Trioxonitrate V acid (Nitric Acid) (HNO₃)

Prepared by: Ostwald Process

Properties:

i. Strong acid

ii. Oxidizing agent

Uses:

i. For manufacture of Fertilizers (ammonium nitrate)

ii. For making Explosives

iii. For Dye and drug manufacture

3. Nitrogen IV Oxide (NO₂)

i. It is a Reddish-Brown gas with choking smell

ii. It is Toxic and contributes to air pollution (one of the gases responsible for acid rain)

iii. Forms acid rain when dissolved in water

4. Dinitrogen I Oxide (Nitrous Oxide) (N₂O)

i. Commonly Known as laughing gas

ii. It is Used as anesthetic in medicine

5. Ammonium Salts (NH₄⁺ compounds)

Examples: NH₄Cl, (NH₄)₂SO₄
Uses:

i. Used as Fertilizers

ii. Used as Electrolytes in dry cells

Nitrogen Cycle (Summary)

Nitrogen is recycled in nature through:

Nitrogen Fixation (by bacteria or lightning)

Nitrification

Assimilation by plants

Ammonification
Denitrification

Environmental Effects

Excess nitrogen compounds can cause:

i. Eutrophication (water pollution)

ii. Acid rain

iii. Global warming (N₂O as greenhouse gas)

Quick Summary

Nitrogen is essential for life but relatively inactive as N₂ gas
Its compounds (NH₃, HNO₃, nitrates) are highly reactive and useful and
Plays a key role in agriculture and industry

Objective Questions

The percentage of nitrogen in the atmosphere is about
A. 21%
B. 50%
C. 78%
D. 90%
Nitrogen belongs to which group in the periodic table?
A. Group 1
B. Group 15
C. Group 7
D. Group 18
The bond between the two nitrogen atoms in N₂ is
A. Single bond
B. Double bond
C. Triple bond
D. Ionic bond
Nitrogen gas is relatively inert because
A. It has low density
B. It forms ions easily
C. It has a strong triple bond
D. It is a metal
The industrial method for producing ammonia is the
A. Contact process
B. Haber process
C. Ostwald process
D. Frasch process
The catalyst used in the Haber process is
A. Platinum
B. Iron
C. Copper
D. Zinc
Which of the following is a basic gas?
A. CO₂
B. NH₃
C. SO₂
D. NO₂
Ammonia is highly soluble in water because it
A. Is non-polar
B. Forms hydrogen bonds
C. Is acidic
D. Is heavy
The process used to manufacture nitric acid from ammonia is
A. Haber process
B. Contact process
C. Ostwald process
D. Cracking
Nitric acid is best described as
A. Weak base
B. Strong acid
C. Neutral compound
D. Salt
Which oxide of nitrogen is known as laughing gas?
A. NO
B. NO₂
C. N₂O
D. N₂O₅
The brown gas observed in air pollution is
A. NO
B. N₂O
C. NO₂
D. NH₃
Which of the following contributes to acid rain?
A. NH₃
B. NO₂
C. N₂
D. CH₄
Ammonium salts contain the ion
A. NH₂⁻
B. NH₄⁺
C. NO₃⁻
D. NO₂⁻
Which of the following is NOT a stage in the nitrogen cycle?
A. Nitrification
B. Assimilation
C. Distillation
D. Denitrification
Nitrogen fixation is the conversion of nitrogen into
A. Oxygen
B. Ammonia
C. Carbon dioxide
D. Hydrogen
Which of the following is used as a fertilizer?
A. NH₄NO₃
B. NaCl
C. CO₂
D. H₂O
Nitrogen does not support combustion because it
A. Is reactive
B. Is inert
C. Is acidic
D. Is alkaline
The oxidation state of nitrogen in NH₃ is
A. -3
B. +3
C. +5
D. 0
The main use of nitric acid is in the manufacture of
A. Plastics
B. Fertilizers
C. Glass
D. Cement

Thursday, 30 April 2026

Carbon and Its Allotropes – at a glance

Carbon is found in Group IV, Period II of the periodic table. Its electronic configuration is 1s² 2s² 2p². It occurs naturally in different forms called allotropes.

Allotropy

Allotropy is the ability of an element to exist in two or more different forms but in the same physical state.

I. Crystalline allotropes: Diamond, Graphite, Fullerenes

Ii. Amorphous forms: Coal, Charcoal, Coke, Soot,

Uses: cutting tools, drilling, jewelry, precision instruments.

Crystalline Allotropes of carbon

1. Diamond

Each carbon atom is bonded to 4 other carbon atoms in a tetrahedral structure. Making diamond a giant molecule with an octahedral shape (Forms a rigid 3D network.)

Properties of diamond

i. It is the Hardest natural substance known

ii. High melting point

iii. It does not conduct electricity

iv. It is Transparent and shiny

Uses:

I. It is used for making Cutting tools

II. It is used as Jewelry

III. It is used for making Industrial drilling machines

2. Graphite

Graphite has flat layers of carbon atoms with free electrons. Each carbon atom in graphite bonds with 3 others forming hexagonal layers.

Each Layers are weakly held together by weak van der walls forces of attraction which makes it easy for one layer to easily slide over another (causing graphite to flake easily)

Properties of graphite

i. Soft and slippery

ii. Good Conductors of electricity (due to free electrons)

iii. It is Black and opaque

iv. It has a high melting point

Uses:

i. It is used in making lead Pencil

ii. It is used as a dry Lubricants

iii. It is used as Electrodes in batteries

iv. It is used for lining the inside of crucibles

3. Fullerenes (Modern Allotrope)

Fullerenes (e.g. C₆₀) are spherical shape (like a football) carbon molecules called buckyballs (Buckminsterfullerene) (C₆₀) or C₇₀ and others – elongated shapes

The carbon atoms are arranged in closed hollow structures such as spheres, ellipsoids, or tubes.

Structure

i. Carbon atoms are arranged in hexagons and pentagons

ii. The most common fullerene is Buckminsterfullerene (C₆₀), which has a spherical shape like a football

iii. Each carbon atom forms three covalent bonds (sp² hybridization)

Properties

I. They have light weight but are very strong.

ii. They are Good electrical conductivity

iii. They have High stability and

iv. They can act as antioxidants

Uses

i. Nanotechnology and electronics

ii. Drug delivery in medicine

iii. They are used as Lubricants

iv. They are used as Superconductors (in some modified forms)

Carbon Nanotubes (cylindrical fullerenes)

Cylindrical tubes made of graphene

Properties

i. They are Very strong

ii. The have Good electrical conductivity

Uses:

I. They are used in Nanotechnology

II. Used in Medicine (for drug delivery)

III. Used in making Electronics

Graphene
Structure: This is a single layer of graphite (one atom thick)
Properties of graphene
i. It is Extremely strong
ii. It is an Excellent conductor of heat and electricity
iii. It is Flexible and lightweight
Uses:
i. It is used in Electronics
ii. It is used in Sensors
iii. It is used in Advanced materials

Amorphous Carbon

i. Charcoal –

a. Wood charcoal absorbs

b. sugar charcoal

c. animal charcoal

Uses

i. absorbs gases and colours

ii. as fuel

ii. Carbon black & lampblack – used in tyres, inks and polish

iii. Coal – used mainly as fuel

Types of Coal (check post on coal): there are four stages of coal

Peat – about 60% carbon
Lignite – about 67% carbon
Bituminous – about 88% carbon
Anthracite – about 94% carbon (hardest and purest)

Destructive Distillation of Coal Heating:

This is when coal is heated to a very high temperature in the absence of air.

The products got are

Coal → Coal gas + Coal tar + Ammoniacal liquor + Coke

Gasification of coke: when coke is heated to red hot and white hot and air and steam blown over it, it produces two types of gases (fuel gases)

i. Producer gas: produced when air is blown over white hot coke C_(s) → CO + N₂

ii.Water gas: Produce when steam is blown over red-hot coke C(s) → CO + H₂

iii. Synthetic gas – CO + H₂

Why Carbon Forms Many Allotropes

Carbon’s ability to form many allotropes is due to:

i. Catenation (bonding with itself)

ii. Ability to form different bond types (single, double)

iii. Flexibility in bonding arrangements

Chemical Properties of Carbon

i. Carbon burns in oxygen to form CO₂ or CO

C_(s) + O_2(s) → CO_(g) (limited oxygen)

C_(s) + O_{2(s),/sub. → CO_2(s) (excess oxygen)}

ii. Combines with elements like sulphur and hydrogen

C_(s) + S_(s) → CS₂

C_(s) + H_{2(g) →} CH₄

iii. Acts as a reducing agent in metal extraction

iv. Fe₂O₃ + C_{(s) →} Fe_(s) + CO_2(g)

Is oxidized by strong acids to form CO₂

2H₂SO_4(aq) + C(s) → 2SO_2(g) + 2H₂O_(g) + CO_2(s)

Objective Questions (Carbon & Its Allotropes)

Carbon belongs to which group in the periodic table?
A. Group I
B. Group II
C. Group IV
D. Group VI
The atomic number of carbon is:
A. 4
B. 6
C. 12
D. 14
The ability of carbon to form long chains is called:
A. Isomerism
B. Catenation
C. Polymerization
D. Hybridization
Which of the following is an amorphous form of carbon?
A. Diamond
B. Graphite
C. Charcoal
D. Fullerene
Diamond is hard because:
A. It contains free electrons
B. It has strong covalent bonds in a 3D network
C. It is metallic
D. It contains impurities
Which allotrope of carbon conducts electricity?
A. Diamond
B. Graphite
C. Charcoal
D. Coke
In graphite, each carbon atom is bonded to how many other carbon atoms?
A. 2
B. 3
C. 4
D. 6
The structure of diamond is:
A. Layered
B. Planar
C. Tetrahedral
D. Linear
Which allotrope of carbon is used as a lubricant?
A. Diamond
B. Graphite
C. Coal
D. Coke
The black soot obtained from incomplete combustion is called:
A. Coke
B. Charcoal
C. Lampblack
D. Coal tar
Which allotrope of carbon is the hardest natural substance?
A. Graphite
B. Diamond
C. Coke
D. Charcoal
Fullerenes are composed of carbon atoms arranged in:
A. Chains
B. Sheets
C. Spherical shapes
D. Cubes
Which of the following is NOT an allotrope of carbon?
A. Graphene
B. Diamond
C. Silicon
D. Fullerene
The valency of carbon is:
A. 2
B. 3
C. 4
D. 6
Coal is mainly composed of:
A. Hydrogen
B. Oxygen
C. Carbon
D. Nitrogen
Which allotrope has a layered structure with weak forces between layers?
A. Diamond
B. Graphite
C. Fullerene
D. Charcoal
Which of the following is used in cutting tools?
A. Graphite
B. Diamond
C. Coke
D. Coal
The presence of free electrons in graphite makes it:
A. Hard
B. Transparent
C. Conductive
D. Brittle
Which form of carbon is used in water purification?
A. Activated charcoal
B. Diamond
C. Graphite
D. Fullerene
The difference between diamond and graphite is mainly due to:
A. Atomic number
B. Number of electrons
C. Arrangement of atoms
D. Chemical composition

Tuesday, 28 April 2026

COAL at a glance

SEO Keywords

Coal formation stages
Types of coal and uses
Properties of coal
Coalification process
Anthracite vs bituminous coal
Fossil fuels explained

Introduction

Coal is a fossil fuel formed from the remains of plants that lived millions of years ago. It is mainly composed of carbon and is one of the most important sources of energy used for electricity generation and industrial processes.

Coal is formed through a slow process called carbonization, where plant materials are buried under sediments and exposed to heat and pressure over time.

Formation of Coal

Coal formation began during ancient geological periods such as the , when dense forests existed.

Process of Formation

Plants absorb carbon dioxide during photosynthesis.
Dead plants accumulate in swampy areas.
Layers of sediment cover the plant material.
Heat and pressure increase over millions of years.
Gradual conversion into different forms of coal.

Stages of Coal Formation (Coalification)

Coal forms in stages, with increasing carbon content and energy value:

1. Peat This is the first stage of coal formation ( also known as coal in the making)

It Contains partially decayed plant material

i. It has Low carbon content (~50–60%)

High moisture content
Burns with a lot of smoke

2. Lignite (Brown Coal)

Soft and brown in color
Higher carbon content than peat (~60–70%)
Low heating value
Contains moisture

3. Bituminous Coal

Most commonly used coal
Black and relatively hard
Higher carbon content (~70–85%)
Produces more heat
Used in industries and electricity generation

4. Anthracite

Highest grade of coal
Very hard and shiny
Highest carbon content (~90–95%)
Burns with a clean, smokeless flame
Highest energy value

Types of Coal

Coal is generally classified based on its carbon content and energy value:

Type	Carbon Content	Characteristics	Uses
Peat	Low	Soft, moist	Limited fuel
Lignite	Moderate	Brown, crumbly	Power generation
Bituminous	High	Black, widely available	Industrial fuel
Anthracite	Very high	Hard, clean burning	Domestic & industrial

Properties of Coal

1. Physical Properties

Color: Brown to black
Texture: Soft (peat) to hard (anthracite)
Lustre: Dull to shiny
Density: Increases with carbon content

2. Chemical Properties

Mainly composed of carbon, with hydrogen, oxygen, nitrogen, and sulfur
Produces carbon dioxide (CO₂) when burned
May release sulfur compounds causing pollution

3. Combustion Properties

Burns to produce heat energy
Calorific value increases from peat → anthracite
Some types produce smoke and soot

4. Coking Property

Certain coals (especially bituminous) can soften and form coke when heated in the absence of air
Coke is used in iron and steel production

Uses of Coal

Generation of electricity in power plants
Production of coke for metallurgy
Industrial fuel
Production of chemicals such as coal tar and ammonia

Advantages of Coal

Abundant and relatively cheap
High energy output
Easy to store and transport

Disadvantages of Coal

Non-renewable resource
Causes air pollution (CO₂, SO₂ emissions)
Contributes to global warming
Mining can damage the environment

Conclusion

Coal remains a major energy source worldwide despite environmental concerns. Understanding its stages, types, and properties helps explain its wide range of uses and its impact on the environment.

Objectives questions

Coal is primarily composed of
A. Hydrogen
B. Carbon
C. Oxygen
D. Nitrogen

The process by which coal is formed from plant remains is called
A. Distillation
B. Carbonization
C. Combustion
D. Crystallization

Which of the following is the lowest grade of coal?
A. Anthracite
B. Bituminous
C. Lignite
D. Peat

The highest grade of coal with the highest carbon content is
A. Lignite
B. Peat
C. Anthracite
D. Coke

Which type of coal is most commonly used in industries?
A. Peat
B. Lignite
C. Bituminous
D. Anthracite

Coal that burns with little or no smoke is
A. Lignite
B. Bituminous
C. Anthracite
D. Peat

The stage that comes immediately after peat in coal formation is
A. Anthracite
B. Lignite
C. Coke
D. Charcoal

Which of the following products is obtained from coal processing?
A. Ethanol
B. Coal tar
C. Glucose
D. Methane

The formation of coke from coal involves heating in the absence of
A. Water
B. Oxygen
C. Nitrogen
D. Hydrogen

Which of the following is a disadvantage of coal?
A. High energy output
B. Easy storage
C. Causes air pollution
D. Abundant supply

Answer Key

Hydrogen and Its Compounds

Hydrogen is the lightest and simplest element in the periodic table.

i. Symbol: H

ii. Atomic number: 1

iii. Electronic configuration: 1s¹

It is a colourless, odourless, and tasteless gas.

Hydrogen is unique because it can behave like both:

i. Alkali metals (Group I) → loses 1 electron

ii. Halogens (Group VII) → gains 1 electron

Occurrence of Hydrogen

Hydrogen is the most abundant element in the universe, but it is not found as a free element on Earth. It occurs mainly in the combined state in:

i. Water (H₂O)

ii. Hydrocarbons (petroleum, natural gas)

ii. Acids and organic compounds

Laboratory Preparation of Hydrogen

Hydrogen is commonly prepared by reacting metals with dilute acids:

Zn + 2HCl → ZnCl2 + H2

Apparatus used:

Conical flask
Delivery tube
Water trough (for collection)

Industrial Preparation of Hydrogen

(a) Electrolysis of Water

Water is decomposed into hydrogen and oxygen using electricity.

(b) Steam Reforming

Methane reacts with steam at high temperature:

CH4 + H2O → CO + 3H2

Physical Properties of Hydrogen

i. Colourless, odourless gas

ii. Very light (least dense gas)

iii. Slightly soluble in water

iv. Highly combustible

Chemical Properties of Hydrogen

(a) Combustion

Hydrogen burns in oxygen to form water:

2H2 + O2 → 2H2O

(b) Reducing Property

Hydrogen reduces metal oxides:

CuO + H2 → Cu + H2O

(c) Reaction with Non-metals

i. With chlorine → HCl

ii. With nitrogen → NH₃

Uses of Hydrogen

i. Manufacture of ammonia (Haber Process)

ii. Hydrogenation of oils (margarine production)

iii. Fuel (rocket fuel, clean energy)

iv. Welding (oxy-hydrogen flame)

Activity Series of Hydrogen

This is an arrangement of metals based on their ability to displace hydrogen from cold water, steam or acids. The activity series helps us predict whether a metal can displace hydrogen from acids.

Activity Series (Simplified)

K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu, Ag, Au

Key Idea:

1. Metals above hydrogen → react with dilute acids to produce hydrogen gas

2. Metals below hydrogen → do NOT produce hydrogen gas

Examples:

Zinc + Acid → Hydrogen produced
Copper + Acid → No reaction

Important Reactions

Zn + H2SO4 → ZnSO4 + H2

Cu + HCl → (No reaction)

Compounds of Hydrogen

1. Water (H₂O)

Properties:

i. Colourless liquid

ii. Neutral (pH ≈ 7)

iii. Universal solvent

Uses:

i. Drinking

ii. Industrial cooling

iii. Chemical reactions

2. Hydrogen Chloride (HCl)

i. It is a colourless gas with pungent smell

ii. It is forms hydrochloric acid in water

Uses:

i. Cleaning metals

ii. Laboratory reagent

3. Ammonia (NH₃)

i. It is a colourless gas with sharp pungent smell

ii. It is highly soluble in water

Uses:

i. It is used in manufacturing Fertilizers

ii. It is used as aRefrigeration

iii. It is used as Cleaning agents

4. Hydrogen Sulphide (H₂S)

i. Colourless gas with rotten egg smell

ii. Toxic and poisonous

Test:

Turns lead(II) ethanoate paper black

5. Methane (CH₄)

i. Simplest hydrocarbon

ii. Main component of natural gas

Uses:

i. Fuel

ii. Chemical production

6. Safety Precautions

i. Hydrogen is highly flammable → avoid open flames

ii. H₂S is toxic → handle in well-ventilated areas

iii. Always test gases properly in the lab

Summary

i. Hydrogen is the lightest element and very reactive

ii. It acts as a reducing agent

iii. Metals above hydrogen in the activity series produce H₂ gas

iv. Important compounds include water, ammonia, HCl, H₂S,

SULPHUR AND ITS COMPOUNDS note

SULPHUR

Sulphur is found in group VI period II in the Periodic Table. It occurs as a free element found in underground deposits. It is also found in the combined state as metallic Sulphide and as tetraoxosulphate (IV).

ELECTRONIC STRUCRURE OF SULPHUR

Extraction of Sulphur by the Frasch Process

The Frasch Process is an industrial method used to extract sulphur from underground deposits. It is especially useful when sulphur is found deep below the earth’s surface, making traditional mining difficult.

In this process, a set of three concentric pipes is drilled down into the sulphur deposit. Superheated water (at about 160–170°C) is pumped through the outermost pipe to melt the sulphur underground, since sulphur has a relatively low melting point.

Next, hot compressed air is forced down the innermost pipe. This creates pressure that pushes the molten sulphur up through the middle pipe to the surface.

The sulphur obtained is usually very pure (about 99.5%) and requires little further purification.

Key Advantages

I. Produces high-purity sulphur

ii. Reduces the need for traditional mining

iii Efficient for deep underground deposits

Simple Summary

The Frasch Process melts underground sulphur using hot water and then forces it to the surface using compressed air.

ALLOTROPES OF SULPHUR

There are two main crystalline allotropes of Sulphur they are: -

1 Rhombic Sulphur: This is a bright yellow octahedral crystalline solid made up of S₈ molecules. It is stable below 96^oC.

2 Monoclinic Sulphur: This is a needle like crystalline molecule consisting of S8. It has an amber colour and is stable at temperatures above 96^oC. It easily reverts to Rhombic below 96^oC. The transition temperature between Rhombic and Monoclinic is 96^oC.

Comparison of the Physical Properties of Rhombic and Monoclinic Sulphur

	Rhombic sulphur	Monoclinic sulphur
Colour	Bright yellow	Amber
Shape	Octahedral	Needle-shaped
Density	2.80 g/cm³	1.98g/cm³
Melting point	113⁰C	119^oC
Stability	Stable below 96^oC	Stable above 96^oC

There are other non crysatlline allotropes of Sulphur such as

1. Amorphous sulphur: formed when sulphur is dissolved in carbon(IV) sulphide and the solution is allowed to evaporate.

2. Plastic sulphur: formed when molten Sulphur is suddenly poured into cold water:00

PHYSICAL PROPERTIES

1. Sulphur is a yellow solid.

2. It melts at 119^oC and boils at 444^oC

3. It is insoluble in water but soluble in carbon (IV) sulphide and toluene

3. It is a poor – conductor of heat and electricity.

CHEMICAL PROPERTIES

1. It reacts directly with metals to form sulphide (S^2-)

Fe_(s) + S_(s) → FeS_(s)

2 It reacts with hydrogen to form hydrogen sulphide;

H_2(g) + S_(s) → H₂S_(g)

3. It reacts with excess oxygen to form sulphur (IV) oxide

O_2(g) + S_(s) →SO_2(g)

4. It reacts with coke (carbon) to form carbon (II) sulphide

C(s) + S(s) → CS2

USES

1. It used in manufacturing tetraoxosulphate (IV) acid

2. It used in vulcanization of rubber

3. It used as germicides

4. It used in manufacturing bleaching agent

COMPOUNDS OF SULPHUR

1. HYDROGEN SULPHIDE, H2S

Hydrogen sulphide is found in volcanic gases, sulphur springs, coal gas and natural gas.

LABORATORY PREPARATION

Hydrogen sulphide is prepared in the laboratory by the action of dilute acids on metallic sulphide like Iron (II) sulphide

2HCl_(aq)+ FeS_(s) → FeCl_2(aq) + H₂S_(g)

The Kipp’s apparatus is used for regular supply of hydrogen sulphide in the laboratory.

PHYSICAL PROPERTIES of Hydrogen sulphide

1. It is a colourless gas

2. It smells like that of rotten egg.

2. It is a poisonous gas

3. It is about 1.18 times denser than air.

4. It is moderately soluble in water to form very weak acidic solution.

5. It burns with pale blue flame.

CHEMICAL PROPERTIES

1. As an acid it reacts with alkali to form a normal salt and water

2NaOH_(aq) + H₂S_(g) → Na₂S_(aq) +2H₂O_(l)

2. It reacts with excess oxygen to form sulphur (VI) oxide but forms deposit of sulphur with limited oxygen

2H₂S_(g) + 3O_2(g) → 2H₂O_(l) + 2SO_2(g)

2H₂S_(g) + O_2(g) → 2H_2(l) + 2S_(s)

3. As a reducing agent, it reacts with many oxidizing agents such as acidified KMnO₄, acidified K₂Cr₂O₇, chlorine gas, FeCl₂, SO₂, H₂SO₄ and HNO₃

TEST FOR HYDROGEN SULPHIDE

Moistened a piece of filter paper with lead (II) trioxonitrate (V) solution and dropped it into a gas jar of the unknown gas. If the paper turns black, then the gas is H₂S.

SULPHUR (IV) OXIDE, SO₂

LABORATORY PREPARATION

It is prepared in the laboratory by heating sodium or potassium trioxosulphate (IV) with tetraoxosulphate (VI) acid or hydrochloric acid.

Na₂SO_3(aq)+2HCl_(aq) → 2NaCl_(aq)+ H₂O(l) + SO_2(g)

Physical Properties of sulphur (IV) oxide

1. Sulphur (IV) oxide is a colourless poisonous gas.

2. It smell like that of burning matches.

2. It is very soluble in water.

3. It is about 2.5 times denser than air.

Chemical Properties

1. As an acid: - it reacts with alkali to form normal salt and water only.

2NaOH_(aq)+ SO_2(g) → Na₂SO_3(aq) + H₂O_(l)

2. As reducing agent: - Sulphur (IV) oxide reduces oxidizing agents such as acidified KMnO₄; acidified K₂Cr₂O₇; FeCl₃, HNO₃, chlorine gas. It decolorizes acidified purple KMnO₄ and turns acidified orange K₂Cr₂O₇ to green.

3. As an oxidizing agent: -Sulphur (IV) oxide reacts as oxidizing agent in the presence of strong reducing agent such as hydrogen sulphide.

2H₂S_(g) + SO_2(g) → 2H₂O_(l) + 3S_(s)

C_(s)+ SO_2(g)→CO_2(g)+ S_(s)

4. As a bleaching agent: - It decolourising dye by its bleaching action. The bleaching action is similar to that of chlorine becausewater must be present.

But, while chlorine bleaches by oxidation sulphur IV oxide bleaches by reduction.

USES of sulphur (IV) oxide

1.It is used in manufacture of tetraoxosulphate (VI) acid.

2. It is used as a germicide and a fumigant especially for destroying termites.

3. It is used as bleaching agent for straw, silt and wood.

4. It is used as preservative in some liquid e.g orange juice.

5. Liquid sulphur (IV) oxide is used as refrigerant.

Test for SO2

1. When sulphur (IV) oxide gas is bubbled through a solution of either acidified potassium heptaoxodichromate (VI) or potassium tetraoxomanganate (VII), it changes the colour of acidified K₂Cr₂O₇ from orange to green or it changes the colour of acidified KMnO₄ purple to colourless.

SULPHUR (VI) OXIDE, SO₃

Sulphur (VI) oxide is prepared by reacting sulphur (IV) oxide and oxygen at 450^oC and 1 atm pressure in the presence of vanadium (V) oxide or platinized asbestos as catalyst

2SO_2(g) + O_2(g) →2SO_3(g)

PHYSICAL PROPERTIES OF SO₃

1. It is a white needle-like crystal at room temperature.

2. It has a low boiling point and vapourizes on gentle heating.

3 It dissolves readily in water to give tetraoxosulphate (VI) acid.

TRIOXOSULPHATE (IV) ACID, H₂SO₃

Trioxosulphate (IV) acid is a dibasic acid with a molecular formula H₂SO₃

Laboratory Preparation OF H₂SO₃

It is prepared in the lab by the action of dilute hydrochloric acid on heated sodium trioxosulphate (IV) to produce sulphur (IV) oxide, which is then dissolved in water.

Na₂SO_3(s)+2HCl_(aq)→2NaCl_(aq) + H₂O_(l) + SO_2(g)

H₂O_(l)+ SO_2(g) → H₂SO_3(aq)

Sulphur (IV) Oxide is the acid anhydride of trioxosulphate (IV) acid.

PHYSICAL PROPERTIES OF H₂SO₃

1. It is colourless liquid.

2. It is readily soluble in water.

3. It has an irritating and choking smell.

Chemical Properties oF H₂SO₃

1. It reacts with alkalis to form salt and water.

2NaOH_(aq) + H₂SO_3(aq)→ Na₂SO_3(aq)+ 2H₂O_(l)

2. It oxidises in air to tetraoxosulphate (VI) acid

2H₂SO_3(aq)+ O_2(g) → 2H₂SO_4(aq)

3. As a reducing agent: - It reduces oxidizing agent like acidified KMnO₄and acidified K₂Cr₂O₇

4 It bleaches dyes in the presence of water.

Test for SO₃^2-

Add a little amount of barium chloride solution to a solution of the unknown substance. If a white precipitate is formed which is soluble in dilute hydrochloric acid then the presence of a trioxosulphate (IV) ion is confirmed.

USES OF H₂SO₃

1. It is used for bleaching straw and other fabrics.

2. It is used as a germicide.

TETRAOXOSULPHATE VI ACID, H₂SO₄

Tetraoxosulphate VI acid is one of the most important chemical compounds known. It is used in almost every manufacturing process; hence it is mostly prepared industrially.

INDUSTRIAL PREPARATION OF H₂SO₄

It is manufactured industrially by Contact process. The following equations summarizes the steps involved in the Contact process.

1. Sulphur is burnt in dry air to obtain sulphur (IV) oxide, SO₂

S_(s) + O_2(g) → SO₂(g)

2.The Sulphur (IV) oxide produced is combined with excess oxygen in the presence of vanadium V oxide (V₂O₅ ) as catalyst at a temperature of 450^oC to yield sulphur (VI) oxide.

SO₂(g) + O_2(g) → 2SO_3(g) + heat

3. The sulphur (VI) oxide is then dissolved in concentrated H₂SO₄ to produce a thick oily liquid called Oleum.

H₂SO_4(aq) + SO_3(g)→ H₂S₂O_7(aq)

4. The Oleum is then combined with one mole of water to produce about 98% tetraoxosulphate (VI) acid.

H₂O_(l)+ H₂S₂O_7(aq)2H₂SO_4(aq)

NOTE: Dissolving Sulphur (VI) oxide in water directly is highly exothermic and will cause the acid to vaporize, producing a mist of droplets of the concentrated acid which can spread and cause acid burns.

PHYSICAL PROPERTIES

1. It is a colourless, viscous liquid with density of 1.84gcm^-3

2. It is corrosive and cause burns when in contact with the skin.

3. It is highly soluble in water evolving large amount of heat.

CHEMICAL PROEPERTIES

1. As an acid,

i. It reacts with metals higher than hydrogen in the electrochemical series to liberate hydrogen gas

Mg_(s)+ H₂SO_4(aq)→ MgSO_4(aq)+ H_2(g)

ii. It reacts with bases to form salts and water ZnO_(s)+H₂SO_4(aq) →ZnSO_4(aq)+H₂O_(l)

iii. It reacts with alkali to form normal and acidic salt

H₂SO_4(aq)+KOH_(aq)→NaHSO_4(aq)+ H₂O_(l)

H₂SO_4(aq)+ KOH_(aq)→ Na₂ SO_4(aq) + 2H₂O_(l)

iv.. It reacts with trioxocarbonate (IV) to liberate carbon (IV) oxide

H₂SO_4(aq)+CuCO_3(aq)→CuSO_4(aq)+ H₂O_(l) + CO_2(g)

2. As oxidizing agent: - Concentrated H₂SO₄ oxidise metals and non –metals to yield the corresponding tetraoxosulphate VI and itself reduced to SO2. It oxidises hydrogen sulphide to Sulphur.

Cu_(s)+ 2H₂SO_4(aq)→ CuSO_4(aq)+ 2H₂O_(l)+SO_2(g)

C_(s) + 2H₂SO_4(aq)→2H₂O_(l)+ CO_2(g)+ 2SO_2(g)

H₂SO_4(aq)+ H₂S_(g)→S_(s)+H₂O_(l)+ SO_2(g)

3. As a dehydrating agent: - Concentrated tetraoxosulphate (VI) acid also behaves as a dehydrating agent, removing components of water from compounds like sugar and ethanedioic acid

C₁₂H₂₂O_11(s)→12C_(s)+11H₂O_(l)

^{sugar charcoal}

COOH

| + H2SO4 → CO2 + CO + H2O

COOH conc

4. Concentrated tetraoxosulphate (VI) displaces volatile acids from their salts

NaCl_(s)+H₂SO_4(aq)→NaHSO_4(aq) + HCl_(g)

Test for SO₄^2-

Add Barium chloride solution to a solution of the unknown salt. If a white precipitate is formed which is insoluble in excess dilute hydrochloric acid, then the presence of a tetraoxosulphate (VI) ion is confirmed.

USES OF H₂SO₄

1. It is used as an electrolyte in lead accumulator.

2. It is used in production of fertilizers e.g ammonium tetraoxosulphate (VI).

3. It is used in purification of crude oil.

4. It is used as drying agent for many gases except NH₃ and H₂S gas.

5 It is used to clean metals before electroplating.

6. It is used in the production of fibres

7. It is used in the manufacture of synthetic detergents

TETRAOXOSULPHATE (VI) SALTS: -

These are the salts formed when metals, bases or alkalis and trioxocarbonate IV reacts with H2SO4

USES OF TETRAOXOSULPHATE (VI) SALTS

1. Ammonium tetraoxosulphate (VI) (NH4)2SO4 used as fertilizers

2. Sodium tetraoxosulphate (VI) (Na2SO4) is used in paper manufacture and as a purgative

3. Calcium tetraoxosulphate (VI) (CaSO4) is mined as gypsum and is used as plaster of Paris (POP) used to set broken bones.

4. Aluminum tetraoxosulphate (VI) (Al2(SO4)3) is used to coagulate precipitate in purification of water (alum)

5. Iron II tetraoxosulphate (VI) is used to treat anemia.

OBJECTIVE QUESTIONS

1. Sulphur belongs to which group in the periodic table?
A. Group I
B. Group IV
C. Group VI
D. Group VII

2. The most common allotrope of sulphur at room temperature is:
A. Monoclinic sulphur
B. Plastic sulphur
C. Rhombic sulphur
D. Amorphous sulphur

3. Which colour is associated with sulphur?
A. Red
B. Yellow
C. Blue
D. Green

4. Sulphur is mainly extracted using the because:
A. It is cheap
B. It produces impure sulphur
C. Sulphur is found underground
D. It requires no heat

5. Which of the following is NOT an allotrope of sulphur?
A. Rhombic
B. Monoclinic
C. Plastic
D. Diamond

6. Sulphur dioxide has the chemical formula:
A. SO
B. SO₂
C. SO₃
D. S₂O

7. The oxidation state of sulphur in SO₂ is:
A. +2
B. +4
C. +6
D. −2

8. Sulphur dioxide acts mainly as a:
A. Reducing agent
B. Oxidizing agent
C. Catalyst
D. Base

9. Which gas is formed when sulphur burns in air?
A. Hydrogen sulphide
B. Sulphur trioxide
C. Sulphur dioxide
D. Carbon dioxide

10. The gas with a rotten egg smell is:
A. SO₂
B. H₂S
C. CO₂
D. NH₃

11. Hydrogen sulphide turns lead(II) ethanoate paper:
A. Blue
B. Red
C. Black
D. White

12. The contact process is used in the manufacture of:
A. Hydrochloric acid
B. Nitric acid
C. Sulphuric acid
D. Carbonic acid

13. The catalyst used in the is:
A. Iron
B. Nickel
C. Vanadium(V) oxide
D. Platinum

14. Oleum is a solution of:
A. SO₂ in water
B. SO₃ in H₂SO₄
C. H₂SO₄ in water
D. SO₂ in H₂SO₄

15. Sulphuric acid is best described as:
A. Weak acid
B. Strong acid
C. Neutral compound
D. Organic acid

16. Which of the following reacts with dilute sulphuric acid to produce hydrogen gas?
A. Copper
B. Zinc
C. Silver
D. Gold

17. The drying agent commonly used in laboratories is:
A. NaCl
B. H₂SO₄ (conc.)
C. HCl
D. NaOH

18. Sulphur trioxide reacts with water to form:
A. H₂SO₃
B. H₂SO₄
C. H₂S
D. SO₂

19. Acid rain is mainly caused by:
A. CO₂
B. SO₂
C. O₂
D. H₂

20. Plastic sulphur is formed when:
A. Sulphur is slowly cooled
B. Molten sulphur is rapidly cooled
C. Sulphur reacts with oxygen
D. Sulphur is heated gently

THEORY QUESTIONS

(I). Name the process represented by the chart

ii). Identify reactant X and product Y.

iii). What are the operating temperature and pressure at stage II

iv). Mention the stage which requires a catalyst and state the catalyst used.

v) give the reason why the SO3 produced in stage II is not dissolved directly in water.

2.(a). State two physical properties of hydrogen sulphide

(ii). Name the laboratory equipment used for intermittent production of hydrogen sulphide?

b. What property of hydrogen sulphide is illustrated in the reaction represented by the following equation?

H2S + 2NaOH ---> Na2S + H2O

Thursday, 16 April 2026

SOLUBILITY at a glance

Solubility:

Solubility of a solute in a solvent is the maximum amount of a solute in moles or in grams that can dissolve/ saturate 1dm3 of solution at a particular temperature.

For example, sugar dissolving in water is a common illustration of solubility.

Solubility of a solute depends on several factors:

i. Nature of solute and solvent: “Like dissolves like” — polar substances dissolve in polar solvents, and non-polar in non-polar.

ii. Temperature: For most solid solutes, solubility increases with increase in temperature, while for gases solubility generally decreases with increase in temperature

iii. Pressure: Mainly affects gases; higher pressure increases the solubility of gases in liquids.

A solution can be:

i. Unsaturated : one that can still dissolve more solute at a particular temperature.

ii. Saturated : one that contains the maximum amount of solute it can hold at a particular temperature in the presence of undissolved solute particles

iii. Supersaturated : one that contains more solute than it can normally hold at a particular temperature (and is unstable).

Determination of Solubility

Solubility is commonly determined experimentally by preparing a saturated solution at a known temperature and then

Weigh the remaining solute.

Solubility is then calculated using:

Solubility= Mass of solute x 100

Mass of solvent

It is often expressed as grams of solute per 100 g of solvent.

A solubility curve is a graph that shows how the solubility of a substance changes with temperature.

To generate a solubility curve for salts like NaCl, Na₂SO₄, KNO₃, Na₂CO₃, and Ca(OH)₂, we usually rely on experimental data plotted as a graph.

Sample Solubility Data (g per 100 g of water)

Temperature (°C)	NaCl	KNO₃	Na₂SO₄	Na₂CO₃	Ca(OH)₂
0.	36	13	5	7	0.19
20	36	32	20	22	0.17
40	37	64	45	48	0.14
60	37	110	30	50	0.12
80	38	170	10	46	0.10
100	39	245	5	45	0.08

How the Solubility Curves Look

If you plot this data (Temperature on x-axis, Solubility on y-axis), you’ll observe:

NaCl (Sodium chloride)
Almost a flat line → solubility changes very little with temperature.
KNO₃ (Potassium nitrate)
A steep upward curve → solubility increases rapidly with temperature.
Na₂SO₄ (Sodium sulfate)
Shows a peak (unusual behavior) → increases up to about 40°C, then decreases (due to change in crystal form).
Na₂CO₃ (Sodium carbonate)
Moderate increase, then slightly levels off at higher temperatures.
Ca(OH)₂ (Calcium hydroxide)
Downward slope → solubility decreases as temperature increases (rare for solids).

A combined solubility curve for different salts highlights how substances respond differently to temperature changes.

While most solids like KNO₃ become more soluble at higher temperatures, some like Ca(OH)₂ show the opposite trend.

Others, like NaCl, remain nearly constant. These variations are important in industrial processes, crystallization, and chemical separation techniques.

Objective Questions

Solubility is defined as the: A. Rate of dissolving a solute
B. Maximum amount of solute dissolved in a solvent at a given temperature
C. Amount of solvent in a solution
D. Volume of solution formed

A solution that can dissolve more solute is said to be: A. Saturated
B. Supersaturated
C. Unsaturated
D. Concentrated

Which of the following factors does NOT affect solubility? A. Temperature
B. Pressure
C. Nature of solute
D. Colour of solute

The solubility of most solid substances in water generally: A. Decreases with temperature
B. Increases with temperature
C. Remains constant
D. Becomes zero

The solubility of gases in liquids: A. Increases with temperature
B. Decreases with temperature
C. Is unaffected by temperature
D. Becomes constant

Increasing pressure increases the solubility of: A. Solids in liquids
B. Liquids in liquids
C. Gases in liquids
D. Solids in gases

A supersaturated solution is: A. Stable
B. Contains less solute than required
C. Contains more solute than it can normally hold
D. Cannot exist

“Like dissolves like” means: A. All substances dissolve in water
B. Polar dissolves polar, non-polar dissolves non-polar
C. Solids dissolve only in solids
D. Liquids dissolve only in gases

Which of the following is an example of a saturated solution? A. Contains no solute
B. Contains maximum solute at a given temperature
C. Contains excess solvent
D. Contains only gas

The unit of solubility is commonly expressed as: A. mol/dm³
B. g/dm³
C. g per 100 g of solvent
D. kg/m³

A solubility curve shows the relationship between: A. Pressure and volume
B. Temperature and solubility
C. Mass and density
D. Volume and pressure

On a solubility curve, a point below the curve represents: A. Saturated solution
B. Supersaturated solution
C. Unsaturated solution
D. Boiling solution

Which substance shows little change in solubility with temperature? A. KNO₃
B. NaCl
C. NH₃
D. CO₂

Which of the following has decreasing solubility with increase in temperature? A. NaCl
B. KNO₃
C. Ca(OH)₂
D. Na₂CO₃

A point above the solubility curve represents: A. Unsaturated solution
B. Saturated solution
C. Supersaturated solution
D. Dilute solution

Solubility depends on: A. Colour only
B. Temperature and nature of substances
C. Shape of container
D. Time of day

When a saturated solution is cooled, crystals may form because: A. Solubility increases
B. Solubility decreases
C. Pressure increases
D. Volume increases

Which of the following best describes a solution? A. A mixture of two solids
B. A homogeneous mixture
C. A heterogeneous mixture
D. A suspension

The process of obtaining solid crystals from a solution is called: A. Filtration
B. Evaporation
C. Crystallization
D. Distillation

Which of the following is least soluble in water at room temperature? A. NaCl
B. KNO₃
C. Ca(OH)₂
D. Na₂CO₃

Wednesday, 15 April 2026

Alkanols (Alcohols) – At a glance

Definition

Alkanols (alcohols) are organic compounds derived from alkanes in which one or more hydrogen atoms are replaced by a hydroxyl group (–OH).

They contain the functional group –OH attached to a saturated carbon atom (sp³ carbon).

General Formula

C_nH_2n+1OH or C_nH_2n+2O

Functional Group

Hydroxyl group (–OH)

This group:

makes alcohols polar
allows hydrogen bonding
increases boiling point
increases solubility in water

Homologous Series

Alcohols belong to a homologous series because:

Same functional group (–OH)
Similar chemical properties
Gradual change in physical properties
Successive members differ by –CH₂

Examples of Alkanols

Name	Molecular Formula	Structural Formula
Methanol	CH₃OH	CH₃–OH
Ethanol	C₂H₅OH	CH₃–CH₂–OH
Propanol	C₃H₇OH	CH₃–CH₂–CH₂–OH
Butanol	C₄H₉OH	CH₃–CH₂–CH₂–CH₂–OH

Classification of Alcohols

Based on the number of alkyl groups attached to the carbon bearing –OH:

Primary (1°)

–OH carbon attached to one alkyl group
Example: Ethanol

R–CH₂–OH

Secondary (2°)

–OH carbon attached to two alkyl groups
Example: Propan-2-ol

R–CH(OH)–R

Tertiary (3°)

–OH carbon attached to three alkyl groups
Example: 2-methyl-2-propanol

R_3C–OH

Physical Properties

State

Lower members → liquids
Higher members → oily liquids/solids

Boiling Point

Higher than alkanes due to hydrogen bonding
Increases with molecular mass

Solubility

Methanol & ethanol → completely miscible with water
Solubility decreases as carbon chain increases

Odour

Mild or characteristic smell

Chemical Properties

Combustion

Alcohols burn in air to form CO₂ + H₂O

Example:

C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O

Reaction with Sodium

Forms sodium alkoxide + hydrogen gas

2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂

Test for alcohol → bubbles of hydrogen gas

Oxidation

Depends on type:

Type	Product formed
Primary	Aldehyde → Carboxylic acid
Secondary	Ketone
Tertiary	No reaction easily

Example:

CH₃CH₂OH → CH₃CHO → CH₃COOH

Dehydration (Removal of water)

Forms alkenes

Using conc. H₂SO₄ or Al₂O₃

C₂H₅OH → C₂H₄ + H₂O

(Ethene formed)

Esterification

Alcohol + Carboxylic acid → Ester + Water

C₂H₅OH + CH₃COOH → CH₃COOC₂H₅ + H₂O

Produces pleasant fruity smell

Preparation of Alcohols

Laboratory Methods

Hydration of alkenes
Fermentation of sugars (ethanol)
Hydrolysis of haloalkanes

Example (Fermentation)

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂

Uses of Alcohols

Alcohol	Uses
Methanol	Fuel, solvent, antifreeze
Ethanol	Drinks, fuel, antiseptic
Propanol	Disinfectant
Butanol	Solvent, perfumes

Safety Notes

Methanol is poisonous
Alcohols are flammable
Avoid inhalation and ingestion in the lab

Quick Summary Table

Property	Key Point
Functional group	–OH
Formula	CₙH₂ₙ₊₁OH
Bonding	Hydrogen bonding
Types	Primary, Secondary and tertiary (1°, 2°, 3°)
Reactions	Combustion, oxidation, esterification, dehydration
Uses	Fuel, solvent, antiseptic

Monday, 13 April 2026

Radioactivity at a glance

RADIOACTIVITY

Meaning of Radioactivity

Radioactivity is the spontaneous disintegration (breakdown) of an element with the emission of energy and radiation.

In this process unstable atoms break down and give off energy in the form of radiation.
Some atoms have too many protons or neutrons in their nucleus, which makes them unstable. To become stable, they release energy.

Types of Radiation

There are three main types of radiation:

Type	Symbol	Nature	Penetration
Alpha	α	Heavy particles	Stopped by paper
Beta	β	Fast electrons	Stopped by thin metal
Gamma	γ	Energy waves	Needs thick lead

Simple Diagram of Radiation

Unstable Atom
      |
      |
   ( Nucleus )
      |
   ___________
  |           |
  |   α   β   γ  → Radiation released
  |___________|

Penetrating Power Diagram

Alpha (α)  → can be stopped by a thin sheet of Paper 
Beta (β)   → can be blocked by a thin a Metal sheet 
Gamma (γ)  →  can be blocked by a thick block of Lead or Concrete.

Examples of Radioactive Elements

Some common radioactive elements are:

Uranium
Radium
Thorium
Carbon-14

Uses of Radioactivity

In Medicine
- Used in X-rays and scanning machines
- Used to treat cancer (radiotherapy)
- Used to sterilise medical equipments
In Industry
- To detect cracks in metal pipes
- To measure thickness of materials
- To fill packaged goods
In Agriculture
- To improve crops
- To kill insects that destroy food
In Science
- Used to determine the age of ancient objects (carbon dating)
- Used to study the structures of organic compounds

Dangers of Radioactivity

Too much radiation can:

Damage body cells
Cause cancer like leukemia
Lead to sickness or death

That is why radioactive materials must be handled carefully.

Conclusion

Radioactivity is a natural process where unstable atoms release energy. It is very useful in medicine, science, and industry, but it can be dangerous if not properly controlled.

Thursday, 9 April 2026

BENZENE long note

BENZENE

Arenes are hydrocarbons with alternating single and double bonds between carbon atoms forming rings. They are classified based on the number of fused rings that is present in the molecule. They have the general molecular formula C_nH_2n-6m, where n is the number of carbon atoms and m is the number of rings. Arene may be monocyclic (contain only one ring) examples include benzene and toluene, or they may be polycyclic (contain more than one ring) examples include anthracene and naphthalene.

Benzene is the simplest arenes.

BENZENE

Benzene is a colorless, sweet-smelling chemical compound that is characterized by its aromatic properties. It is represented by the chemical formula C₆H₆, meaning it consists of six carbon atoms and six hydrogen atoms arranged in a ring structure.

Aromatic hydrocarbons are planer compounds which usually have one or more rings of six carbon atoms, which usually have alternating single and double bonds. The value and the strength of these single and double bonds are identical. To explain these alternating bonds benzene is drawn as a resonance structure showing the alternating bonds.

Structures of benzene

These resonance structures of benzene also known as Kekule’ structures were proposed by a German chemist in1865 know as August Kekule. He proposed that 1. The six carbon atoms in benzene are arranged in a planar hexagonal ring with alternating double and single bonds around the ring.

2. That the pi electrons from the double bonds are delocalized across the entire ring and not localized between individual carbon-carbon bonds.

These resonance structures can be drawn as two hexagons with alternating single and double bonds or as a single hexagon with a circle drawn in the center representing the delocalized pi- electrons.

Kekule Structures of benzene

Benzene Derivatives These are compounds that look like benzene which have benzene as the parent or main compound with one or more of the hydrogens substituted by other groups. Some examples of these compounds include.

I. Methylbenzene (toluene) CH₃

ii. Phenol

iii. Xylene

iv. Nitrobenzene Phenylamine (Aniline)

v. Benzoic acid

Physical Properties of benzene

1. Benzene is a colourless liquid

2. has a sweet smell.

.3. It is insoluble in water.

4. It has a boiling point of 80⁰C

Chemical properties

1. Addition reactions:

i. Addition reactions:

(i) Benzene combines with hydrogen to yield cyclohexane at 180⁰C and presence of Ni catalyst

C₆H₆ + 3H₂ C₆H₁₂ + 3H₂

Benzene Cyclohexane

(ii). Halogenation: Benzene reacts with the halogens to produce cyclic compounds in presence of UV light

C₆H₆ + 3Cl₂ ^{UV light} C₆H₆Cl6

2. Substitution reaction: - benzene undergoes substitution reaction with the halogens to e.g Cl₂, Br₂, I₂ to yield halogenated products. The presence of single bonds in benzene is responsible for its substitution reactions

i. Halogenation

C₆H₆ + Br₂ C₆H₅Br + HBr

ii. In the absence of sunlight using aluminum chloride as catalyst benzene react with chlorine to form chlorobenzene

2. Benzene reacts to form methylbenzene when combined with monochloromethane, the reaction is catalyzed by aluminium chloride

ii. Nitration: This occurs in the mixture of HNO₃ and H₂SO₄ together with benzene.

C₆H₆ + HNO₃ C₆H₅NO₂

iii. Sulphonation:- Benzene reacts with conc. H₂SO₄ to form benzene sulphonic acid.

iv. Alkylation: - These are reactions in which benzene reacts with halo-alkanes in the presence of AlCl₃.

Uses of benzene

1. Benzene and its derivatives like methylbenzene are used as additives to improve the quality of petrol.

2. It is used for the manufacture of some drugs like aspirin.

3. It is used for manufacture of explosives like 2,4,6-trinitromethyl-benzene (TNT)

4. It is used for the manufacture of some dyes.

5. It is used to produce phenylethene (styrene) a monomer used to produce polystyrene.

6. It is used in the preparation of detergents.

7. Preparation of insecticides

NOTE: Benzene is a known carcinogen and should be handled with great care. Avoid prolonged exposure to benzene

Hybridization at a glance

Hybridization

Hybridization is the mixing of atomic orbitals (s and p) to form new orbitals called hybrid orbitals. These hybrid orbitals determine the shape and bonding of molecules.

Types of Hybridization

1. sp Hybridization

Formation: It is formed when one s-orbital mixes with

1 s orbital + 1 p orbital → 2 sp orbitals

s + p ▪︎▪︎▪︎▪︎▪︎>2sp

i. Shape: It is Linear in shape

ii. Bond angle: it has a bond angle of 180°

It occurs mainly in the alkynes with triple bond.

Example :Ethyne (C₂H₂)

Diagram:

H — C ≡ C — H

180°

(straight line)

2. sp² Hybridization

Formation: It is formed when one s orbital mixes with two(2) p orbitals to give 3 hybrid orbitals

1 s orbital + 2 p orbitals → 3 sp² orbitals

s + 2p ▪︎▪︎▪︎▪︎>3sp2

i. Shape: It has a Trigonal planar shape

ii. Bond angle: It has a bond angle of 120°

It is common with the alkenes where double bond is found

Example: Ethene (C₂H₄)

Diagram:

H — C = C — H

(Flat triangular shape, 120°)

3. sp³ Hybridization

Formation: It is formed when one (1) s-orbital mixes with three (3) p-orbitals to form a set of four (4) hybrid orbitals
1 s orbital + 3 p orbitals → 4 sp³ orbitals

s + 3p ▪︎▪︎▪︎▪︎▪︎> 4sp3

i. Shape: The bond is Tetrahedral in shape

ii. Bond angle: It has a bond angle of 109.5°

This type of hybridization is common with the alkanes with single bonds

Example: Methane (CH₄)

Diagram:

H — C — H

(3D shape, like a pyramid)

Quick Comparison

Type	Shape	Angle	Example
sp	Linear	180°	C₂H₂
sp²	Trigonal planar	120°	C₂H₄
sp³	Tetrahedral	109.5°	CH₄

Objective Questions

Here are 10 objective (multiple-choice) questions on hybridization suitable for SS1–SS3 students:

Hybridization Objective Questions

Hybridization is the process of: A. Breaking atomic orbitals
B. Mixing atomic orbitals to form new orbitals
C. Formation of ions
D. Transfer of electrons

Which type of hybridization involves one s and one p orbital?
A. sp²
B. sp³
C. sp
D. sp³d

The shape of an sp³ hybridized molecule is:
A. Linear
B. Trigonal planar
C. Tetrahedral
D. Bent

How many hybrid orbitals are formed in sp² hybridization?
A. 2
B. 3
C. 4
D. 5

Which molecule is sp hybridized?
A. CH₄
B. NH₃
C. CO₂
D. H₂O

The bond angle in sp² hybridization is approximately:
A. 180°
B. 120°
C. 109.5°
D. 90°

Which of the following has sp³ hybridization?
A. C₂H₂
B. CO₂
C. CH₄
D. BF₃

In sp hybridization, the geometry of the molecule is:
A. Tetrahedral
B. Trigonal planar
C. Linear
D. Pyramidal

Which hybridization type is associated with a tetrahedral shape?
A. sp
B. sp²
C. sp³
D. sp³d

In sp³ hybridization, how many p orbitals are involved?
A. 1
B. 2
C. 3
D. 4

Theory Questions

What is hybridization?
State the shape and bond angle of:

(a) sp
(b) sp²
(c) sp³

Which hybridization is found in methane (CH₄)?
What shape is formed in sp² hybridization?
Give one example of a molecule with sp hybridization.

Sunday, 8 March 2026

NATURE OF MATER

What is Matter: -
Mater is defined as anything that has mass and occupies space.

Composition of matter: - matter consist of any one of the following particles. To

1. Atoms.

2. Molecules. Or

3. Ions

1. An Atom is the smallest particle of an element that can take part in a chemical reaction.

2. A molecule is the smallest particle of a substance that exist alone and still possess the properties of the substance. E.g H2O, O

3. An Ion is a charged particle; it is formed when an atom loses or gains electrons. E.g Na+, Cl-

Radicals are group of atoms with a single charge. E.g NO-, SO42-, OH-

Matter generally is made up of any one or more of the particles mentioned above.

States of matter

matter can exist in three states.

i. the solid

ii. the liquid and

iii. the gaseous state.

SOLID: - In solids the particles of matter are densely packed and are held by strong forces of attraction (force of cohesion).

Properties of solids

i., solids have fixed, or definite volumes

ii. solids also have fixed shapes.

iii solids cannot be compressed

Solid state (particles are tightly packed and are held by strong forces)

LIQUIDS: -In liquids the molecules (particles) are close together in an orderly manner with little freedom of movement. Molecules in a liquid are close together but are not held so

rigidly in position and can move past one another.

Properties of Liquids

i. a liquid no fixed or definite shape but it takes the shape of its container,

ii. liquids have a fixed or definite volume

iii. liquids cannot be compressed.

Liquid state (particles are not held tightly together)

GAS: - In a gas, the particles/molecules are separated by distances that are large compared with the size of the molecules.

Properties of gases

i.; gasses have no fixed or definite volume (will occupy entire volume of its container)

ii. gases have no fixed shape.

iii. gases can be compressed

Gases differ from liquids and solids in the distances between their individual particles.

Gases (particles of gases are wide apart)

The three states of matter can be inter-convertible without changing the composition of the substance. Upon heating, a solid it will change into a liquid form at a particular temperature.

The temperature at which this transition occurs is called the melting point of the solid. Further heating will convert the liquid into a gas at a particular temperature called the boiling point of the liquid. Cooling a gas on the other hand, will cause it to change into a liquid, this process is called Condensation. When the liquid is cooled further, it will change into the solid form, and the process is known as Freezing.

Some solids change directly to the gaseous without passing through the liquid state and vice Versal. These processes are both known Sublimation and Deposition.

Changes in the state of Matter

Now remember we defined chemistry as the study of the composition, properties and the uses of mater as well as the principle that underlies the changes that matter undergoes, and so far, we are told that mater consist of one or any two of atoms, molecules or ions. now the properties of matter can be divided into two, that is, physical properties and chemical properties.

PROPERTIES OF MATTER

The properties of matter can be grouped into two

i. Physical properties are those properties that a substance (matter) shows by itself (i.e those properties that you see when you look at, touch or smell the substance) these include Temperature, Pressure, Colour, Smell, Density, Solubility, Melting and boiling points.

ii. Chemical properties on the other hand are those properties that matter exhibits when it comes in contact with other substances like acids, bases, even water to form new substances.

Physical and Chemical change

A physical change is one that is easily reversible and in which no new substance is formed.

example of physical changes is.

i. Dissolving sodium chloride in water

ii. Changing water to ice

iii. Evaporation of liquids

iv. Melting of candle wax

A chemical change is one which is not easily reversible and in which a new substance is always formed.

example of changes is.

i. burning of wood, paper, or clothe.

ii. rusting of iron when exposed to air and moisture.

iii. decomposition of organic matter.

iv. dissolving a metal like calcium or magnesium in dilute acids.

v. the hardening of cement when exposed to air.

OBJECTIVE QUESTIONS

1. Which of the following is a physical change

a). Dissolving sugar on water

b). Addition of acid to base

c). Burñing of wood

d). Rusting of iron

THEORY QUESTIONS

1(i). State two differences between the properties of solids and gasses

(ii). What process does each of X, Y and Z represent in the changes shown below?

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Nature of Matter

Introduction

The nature of matter is a fundamental concept in chemistry that explains what matter is made of and how it behaves. Everything around us — from the air we breathe to the food we eat — is composed of matter. Understanding the nature of matter helps scientists explain physical and chemical changes in substances.

What is Matter?

Matter is anything that has mass and occupies space.

Mass refers to the amount of substance present, while space occupied by matter is known as volume.

Examples of Matter

Water in a bottle
Air inside a balloon
Sand on a beach
A wooden table

All these substances have mass and occupy space, therefore they are matter.

Characteristics of Matter

Matter possesses several important characteristics:

1. Matter Has Mass

Mass is the quantity of matter in a body. It is measured using a balance and expressed in grams (g) or kilograms (kg).

2. Matter Occupies Space

The space that matter occupies is called volume. For example, water poured into a container fills the available space.

3. Matter Is Made of Tiny Particles

Matter is made up of extremely small particles called:

Atoms
Molecules
Ions

These particles are too small to be seen with the naked eye.

4. Particles of Matter Are Always Moving

The particles that make up matter are in constant motion. The speed of this movement increases when the temperature rises.

5. Particles of Matter Attract Each Other

There are forces of attraction between particles of matter which hold them together.

Particle Nature of Matter

The particle theory of matter states that:

Matter is made up of tiny particles.
The particles have spaces between them.
The particles are constantly moving.
The particles attract one another.

This theory helps explain processes such as diffusion, dissolving, and changes of state.

States of Matter

Matter exists mainly in three states.

1. Solid

Solids have definite shape and definite volume. The particles are tightly packed and can only vibrate in fixed positions.

Examples

Salt
Iron
Wood
Stone

Properties of Solids

Fixed shape
Fixed volume
High density
Particles closely packed

2. Liquid

Liquids have definite volume but no definite shape. They take the shape of the container in which they are placed.

Examples

Water
Oil
Alcohol
Kerosene

Properties of Liquids

Definite volume
No fixed shape
Flow easily
Particles loosely packed

3. Gas

Gases have no definite shape and no definite volume. Their particles are far apart and move freely.

Examples

Oxygen
Carbon dioxide
Nitrogen
Air

Properties of Gases

No fixed shape
No fixed volume
Easily compressed
Particles move rapidly

Changes in the State of Matter

Matter can change from one state to another when heat energy is added or removed.

Change	Description	Example
Melting	Solid → Liquid	Ice turning to water
Freezing	Liquid → Solid	Water forming ice
Evaporation	Liquid → Gas	Water forming vapor
Condensation	Gas → Liquid	Steam forming water droplets
Sublimation	Solid → Gas directly	Camphor or naphthalene

Importance of Studying the Nature of Matter

Understanding the nature of matter helps us to:

Understand chemical reactions
Study properties of substances
Explain changes of state
Develop new materials and medicines
Improve processes in industry and technology

It is also important in fields like medicine, environmental science, engineering, and materials science.

Conclusion

The nature of matter explains the structure, properties, and behavior of substances. Since matter is made up of tiny particles that are constantly moving and attracting each other, many natural phenomena such as diffusion, evaporation, and chemical reactions can be explained through this concept.

Objective Questions

Matter is anything that has ______ and occupies space.
The space occupied by matter is called ______.
The smallest particles that make up matter are called ______.
The state of matter with definite shape and volume is ______.
The process by which a liquid changes to gas is called ______.

Theory Questions

Define matter.
State four characteristics of matter.
Explain the particle nature of matter.
Describe the three states of matter.
Explain two changes of state with examples.

easykemistry

Saturday, 2 May 2026

Occurrence

Important Compounds of Nitrogen

1. Ammonia (NH₃)

Objective Questions

Thursday, 30 April 2026

Allotropy

2. Graphite

3. Fullerenes (Modern Allotrope)

Structure

Properties

Uses

i. Nanotechnology and electronics

ii. Drug delivery in medicine

iii. They are used as Lubricants

iv. They are used as Superconductors (in some modified forms)

Amorphous Carbon

Types of Coal (check post on coal): there are four stages of coal

Destructive Distillation of Coal Heating:

Gasification of coke: when coke is heated to red hot and white hot and air and steam blown over it, it produces two types of gases (fuel gases)

Chemical Properties of Carbon

i. Carbon burns in oxygen to form CO2 or CO

Tuesday, 28 April 2026

SEO Keywords

Introduction

Formation of Coal

Process of Formation

Stages of Coal Formation (Coalification)

1. Peat This is the first stage of coal formation ( also known as coal in the making)

It Contains partially decayed plant material

i. It has Low carbon content (~50–60%)

2. Lignite (Brown Coal)

3. Bituminous Coal

4. Anthracite

Types of Coal

Properties of Coal

1. Physical Properties

2. Chemical Properties

3. Combustion Properties

4. Coking Property

Uses of Coal

Advantages of Coal

Disadvantages of Coal

Conclusion

Answer Key

Zn + 2HCl → ZnCl2 + H2

Apparatus used:

(a) Electrolysis of Water

(b) Steam Reforming

(a) Combustion

(b) Reducing Property

(c) Reaction with Non-metals

Activity Series (Simplified)

Examples:

1. Water (H₂O)

Properties:

Uses:

Uses:

Uses:

Test:

Uses:

Key Advantages

Simple Summary

Thursday, 16 April 2026

Sample Solubility Data (g per 100 g of water)

How the Solubility Curves Look

Wednesday, 15 April 2026

Definition

Alkanols (alcohols) are organic compounds derived from alkanes in which one or more hydrogen atoms are replaced by a hydroxyl group (–OH).

General Formula

Functional Group

Homologous Series

Examples of Alkanols

Classification of Alcohols

Primary (1°)

Secondary (2°)

Tertiary (3°)

Physical Properties

State

i. Carbon burns in oxygen to form CO₂ or CO