Complete Chemistry notes on Carbon and its Compounds for BPSC and Other Competitive Exams in 2025

Complete Chemistry notes on Carbon and its Compounds for BPSC and Other Competitive Exams in 2025

General Science- 12 (Chemistry)

Carbon and its Compounds – Fuel Types, Hydrocarbons

Carbon is a unique element due to its ability to form a vast number of compounds. Its chemistry forms the basis of organic chemistry, which is essential for understanding living organisms and many industrial products.

Introduction to Carbon

Carbon (C) is a non-metal element with atomic number 6. It has 4 valence electrons.

Unique Properties of Carbon:

1. Tetravalency: Carbon has a valency of 4, meaning it can form four covalent bonds with other atoms (carbon or other elements). This allows it to form a wide variety of compounds.
2. Catenation: Carbon atoms have the unique ability to link with other carbon atoms through strong covalent bonds to form long chains, branched chains, or ring structures. This property gives rise to the large number of carbon compounds.
   • The bonds can be single, double, or triple covalent bonds.

Covalent Bonding in Carbon: Carbon forms covalent bonds by sharing its valence electrons with other atoms. This allows both carbon and the other atoms to achieve a stable noble gas configuration.

Allotropes of Carbon

Allotropes are different structural forms of the same element in the same physical state. Carbon exhibits several allotropic forms.

A. Crystalline Allotropes:

1. Diamond:
   • Structure: Each carbon atom is bonded to four other carbon atoms in a rigid three-dimensional tetrahedral structure.
   • Properties: Hardest known natural substance, excellent insulator (does not conduct electricity), high melting point, transparent, highly refractive.
   • Uses: Cutting tools, drilling equipment, abrasive for grinding, jewelry.
2. Graphite:
   • Structure: Carbon atoms are arranged in hexagonal rings, forming layers. These layers are held together by weak Van der Waals forces, allowing them to slide over each other.
   • Properties: Soft and slippery (lubricant), good conductor of electricity (due to free electrons between layers), high melting point, opaque, greyish-black.
   • Uses: Pencil leads, lubricants, electrodes in batteries, moderator in nuclear reactors.
3. Fullerene (e.g., Buckminsterfullerene, C60​):
   • Structure: Carbon atoms are arranged in a spherical shape resembling a football (soccer ball), with 60 carbon atoms forming 12 pentagons and 20 hexagons. Other fullerenes exist (C70​, etc.).
   • Properties: Superconductors at low temperatures, potential for drug delivery, nanotechnology applications.
   • Uses: Research in nanotechnology, catalysts, superconductors.

B. Amorphous Allotropes:

These forms do not have a regular, crystalline structure.

• Coal: A complex mixture primarily of carbon, formed from ancient plant matter.
• Coke: A porous fuel with high carbon content, produced by heating coal in the absence of air.
• Charcoal: A porous black solid, produced by heating wood or animal bones in the absence of air.
• Lampblack (Soot): Fine carbon powder formed from incomplete combustion of hydrocarbons, used in inks and paints.

Hydrocarbons

Hydrocarbons are organic compounds composed solely of carbon and hydrogen atoms. They form the backbone of organic chemistry and are major components of fuels.

Classification of Hydrocarbons:

A. Saturated Hydrocarbons (Alkanes)

• Definition: Hydrocarbons in which all carbon-carbon bonds are single bonds. They are considered “saturated” because they contain the maximum possible number of hydrogen atoms for a given number of carbon atoms.
• General Formula: Cn​H2n+2​ (where ‘n’ is the number of carbon atoms).
• Bonding: Only single covalent bonds (C-C and C-H).
• Common Names (first few):
  • n=1: Methane (CH4​) – simplest alkane, main component of natural gas.
  • n=2: Ethane (C2​H6​)
  • n=3: Propane (C3​H8​) – component of LPG.
  • n=4: Butane (C4​H10​) – component of LPG.
• Properties: Generally unreactive, burn easily.

B. Unsaturated Hydrocarbons

These hydrocarbons contain at least one carbon-carbon double bond or triple bond. They are “unsaturated” because they have fewer hydrogen atoms than their corresponding alkanes and can undergo addition reactions.

1. Alkenes:
   • Definition: Hydrocarbons containing at least one carbon-carbon double bond (C=C).
   • General Formula: Cn​H2n​ (where ‘n’ is ≥2).
   • Bonding: At least one double covalent bond (C=C).
   • Common Names:
     • n=2: Ethene (C2​H4​) – simplest alkene, used in ripening fruits, polymer production (polyethylene).
     • n=3: Propene (C3​H6​)
   • Properties: More reactive than alkanes due to the double bond.
2. Alkynes:
   • Definition: Hydrocarbons containing at least one carbon-carbon triple bond (C≡C).
   • General Formula: Cn​H2n−2​ (where ‘n’ is ≥2).
   • Bonding: At least one triple covalent bond (C≡C).
   • Common Names:
     • n=2: Ethyne (C2​H2​) – commonly known as acetylene, used in welding (oxy-acetylene flame).
     • n=3: Propyne (C3​H4​)
   • Properties: Highly reactive due to the triple bond.

C. Aromatic Hydrocarbons:

• Contain benzene ring structures (e.g., Benzene (C6​H6​)). These have special stability due to delocalized electrons.

Functional Groups

A functional group is an atom or a group of atoms attached to a hydrocarbon chain that is responsible for the characteristic chemical properties of the organic compound. The carbon chain provides the skeleton, while the functional group dictates how the molecule will react.

• Examples:
  • Alcohols: Contain the hydroxyl group (-OH). Example: Ethanol (CH3​CH2​OH)
  • Carboxylic Acids: Contain the carboxyl group (-COOH). Example: Ethanoic acid (CH3​COOH) (acetic acid)
  • Aldehydes: Contain the aldehyde group (-CHO). Example: Methanal (HCHO)
  • Ketones: Contain the carbonyl group (-CO-) within the carbon chain. Example: Propanone (CH3​COCH3​) (acetone)
  • Haloalkanes: Contain a halogen atom (F, Cl, Br, I) attached to a carbon chain. Example: Chloromethane (CH3​Cl)

Homologous Series

A homologous series is a series of organic compounds that have:

• The same functional group.
• Similar chemical properties.
• Successive members differ by a −CH2​− unit.
• A general formula for the entire series.
• Example: Alkanes (CH4​,C2​H6​,C3​H8​,…) form a homologous series. Each successive member differs by one carbon and two hydrogen atoms.

Fuels

A fuel is any substance that produces a significant amount of heat and light energy upon combustion (burning) in the presence of oxygen.

Characteristics of a Good Fuel:

1. High Calorific Value: Produces a large amount of heat per unit mass or volume.
2. Moderate Ignition Temperature: Should ignite easily but not too easily (to prevent accidental fires).
3. Low Moisture Content: Moisture reduces calorific value and produces smoke.
4. Low Non-combustible Matter: Should leave minimal ash or residue.
5. Easy to Store and Transport: Should be safe and convenient.
6. Economical: Should be readily available and affordable.
7. Causes Less Pollution: Should produce minimal harmful byproducts upon combustion.

Types of Fuels (based on their physical state):

A. Solid Fuels:

• Wood: Renewable, but low calorific value and produces smoke.
• Coal: A major fossil fuel, formed over millions of years from plant matter.
  • Types of Coal (increasing carbon content & calorific value):
    • Peat: Lowest carbon content, first stage of coal formation.
    • Lignite (Brown Coal): Lower carbon content, more moisture.
    • Bituminous Coal (Soft Coal): Most common type, good calorific value.
    • Anthracite (Hard Coal): Highest carbon content, highest calorific value, burns cleanly with little smoke.
• Charcoal: Produced from heating wood in absence of air, burns cleaner than wood.
• Coke: Produced from heating coal in absence of air, almost pure carbon, good fuel and reducing agent.

B. Liquid Fuels:

• Petroleum (Crude Oil): A complex mixture of hydrocarbons formed from ancient marine organisms. It is refined to produce various fractions.
  • Refining: Process of separating crude oil into useful fractions based on their boiling points (fractional distillation).
  • Products of Petroleum Refining:
    • Petrol (Gasoline): Used in light vehicles.
    • Diesel: Used in heavy vehicles, generators.
    • Kerosene: Used in jet engines, lamps, stoves.
    • LPG (Liquefied Petroleum Gas): See below.
    • Lubricating Oil, Paraffin Wax, Bitumen (Asphalt).
• Alcohol (Ethanol): Can be used as a fuel, often blended with petrol (gasohol).

C. Gaseous Fuels:

• Natural Gas: Primarily Methane (CH4​), found alongside petroleum deposits.
  • Compressed Natural Gas (CNG): Stored under high pressure, used as a cleaner vehicle fuel.
  • Liquefied Natural Gas (LNG): Natural gas cooled to liquid form for transport.
• Liquefied Petroleum Gas (LPG): Mixture of Propane (C3​H8​) and Butane (C4​H10​), obtained from petroleum refining. Stored as liquid under pressure, used as domestic fuel.
• Biogas: Produced by anaerobic decomposition of animal dung and plant waste (main component is Methane). Renewable.
• Producer Gas: Mixture of CO and N2​, obtained by passing air over hot coke.
• Water Gas: Mixture of CO and H2​, obtained by passing steam over hot coke.

Environmental Impact of Fuels

Combustion of fossil fuels has significant environmental consequences:

1. Carbon Dioxide (CO2​) Emission: A major greenhouse gas, contributing to global warming and climate change.
2. Carbon Monoxide (CO) Emission: Produced by incomplete combustion, a highly toxic gas.
3. Sulfur Dioxide (SO2​) and Nitrogen Oxides (NOx​) Emission: Produced from sulfur and nitrogen impurities in fuels, leading to acid rain (harmful to buildings, forests, aquatic life).
4. Particulate Matter: Fine carbon particles (soot) that cause respiratory problems and reduce visibility.

Practice Questions

1. Which unique property of carbon allows it to form long chains and rings with other carbon atoms?
   • A) Tetravalency
   • B) Isomerism
   • C) Catenation
   • D) Allotropy
   • Rationale: Catenation is the self-linking property of carbon atoms.
2. Which allotrope of carbon is known for being the hardest natural substance and does not conduct electricity?
   • A) Graphite
   • B) Fullerene
   • C) Diamond
   • D) Coal
   • Rationale: Diamond’s rigid 3D structure makes it extremely hard and an insulator.
3. Graphite is used as an electrode in batteries due to its property of:
   • A) High melting point
   • B) Softness
   • C) Good electrical conductivity
   • D) Lustrous appearance
   • Rationale: Its ability to conduct electricity makes it suitable for electrodes.

4. Which of the following is the general formula for alkanes?
   • A) Cn​H2n​
   • B) Cn​H2n−2​
   • C) Cn​H2n+2​
   • D) Cn​Hn​
   • Rationale: Alkanes are saturated hydrocarbons with only single bonds, following the formula Cn​H2n+2​.
5. Ethyne, commonly known as acetylene, belongs to which class of hydrocarbons?
   • A) Alkanes
   • B) Alkenes
   • C) Alkynes
   • D) Aromatic hydrocarbons
   • Rationale: Ethyne contains a carbon-carbon triple bond, classifying it as an alkyne.
6. The functional group present in alcohols is:
   • A) -COOH
   • B) -CHO
   • C) -OH
   • D) -CO-
   • Rationale: The hydroxyl group (-OH) defines an alcohol.

7. Which type of coal has the highest carbon content and calorific value, burning with little smoke?
   • A) Peat
   • B) Lignite
   • C) Bituminous coal
   • D) Anthracite
   • Rationale: Anthracite is the highest rank of coal with the highest carbon content and is the cleanest burning.
8. LPG (Liquefied Petroleum Gas) is primarily a mixture of:
   • A) Methane and Ethane
   • B) Propane and Butane
   • C) Carbon Monoxide and Hydrogen
   • D) Hydrogen and Oxygen
   • Rationale: LPG, used as cooking fuel, mainly consists of propane and butane.
9. Which of the following gases is a major contributor to acid rain, primarily produced from the burning of fossil fuels?
   • A) Carbon dioxide (CO2​)
   • B) Carbon monoxide (CO)
   • C) Sulfur dioxide (SO2​)
   • D) Methane (CH4​)
   • Rationale: Sulfur dioxide and nitrogen oxides (NOx​) are the main precursors to acid rain.
10. What is the primary concern associated with the release of large amounts of carbon dioxide into the atmosphere from burning fuels?
    • A) Depletion of the ozone layer
    • B) Global warming
    • C) Formation of smog
    • D) Water pollution
    • Rationale: Carbon dioxide is a potent greenhouse gas, and its increased concentration in the atmosphere leads to global warming.