Science and Technology Class 9 Notes Chapter 13 Maharashtra Board

Introduction to Carbon

What is an Element?

• An element is a pure substance made of only one type of atom (e.g., carbon, oxygen).
• Types: Metals (e.g., iron), non-metals (e.g., carbon), metalloids (e.g., silicon).

Carbon Basics:

• Carbon is a non-metal element.
• Symbol: C, Atomic Number: 6, Atomic Mass: 12, Electron Configuration: 2,4, Valency: 4.
• Found in nature in free (diamond, graphite) and combined forms (CO₂, carbonates).

Activity (Burning Organic Substances):

• Heat milk in an evaporating dish → black residue (carbon) remains.
• Heat sugar, wool, dry leaves, hair, seeds, pulses, plastic in test tubes → black residue (carbon) forms.
• Conclusion: Organic compounds (from plants/animals) contain carbon, which remains as a black substance after burning.

What is a Compound?

• A compound is a substance formed when two or more elements chemically combine (e.g., H₂O).
• Organic Compounds: Contain carbon, derived from living things (e.g., sugar, proteins).
• Inorganic Compounds: From minerals, may or may not contain carbon (e.g., NaCl, CaCO₃).

Importance of Carbon:

• Found in daily items: food (carbohydrates, proteins), clothes (cotton, wool), fuels (coal, petrol), DNA/RNA (heredity).
• Organic chemistry is the study of carbon compounds (started by Wohler, who made urea from ammonium cyanate).

Occurrence of Carbon

In Nature:

Free State: As diamond, graphite, fullerene.

Combined State:

• Carbon dioxide (CO₂) in air (0.03%).
• Carbonates: CaCO₃ (limestone, marble), ZnCO₃ (calamine).
• Fossil Fuels: Coal, petroleum, natural gas.
• Nutrients: Carbohydrates, proteins, fats.
• Fibers: Cotton, wool, silk.

In Earth’s Crust: 0.27% (as carbonates, coal, petroleum).

Properties of Carbon

Allotropy:

• Some elements exist in different forms with the same chemical properties but different physical properties (e.g., carbon, sulphur).
• Carbon has crystalline (diamond, graphite, fullerene) and non-crystalline (coal, charcoal, coke) forms.

1. Crystalline Allotropes:

• Have a regular arrangement of atoms, definite shape, high melting/boiling points.

Diamond:

• • Found in: Golconda (Telangana), Panna (Madhya Pradesh), South Africa, Brazil.
  • Structure: Each carbon atom bonded to 4 others (3D structure), very hard.
• Properties:
  • • Hardest natural substance, density 3.5 g/cm³, melting point 3500°C.
    • Burns at 800°C in oxygen to form CO₂ only.
    • Does not dissolve in solvents, unaffected by acids/bases.
    • Bad conductor of electricity (no free electrons).
  • Uses:
    • Glass cutting, rock drilling, eye surgery (diamond knives).
    • Ornaments, polishing diamonds, radiation-proof windows in satellites.

Graphite:

• • Found in: Russia, New Zealand, America, India.
  • Structure: Each carbon atom bonded to 3 others, forming hexagonal layers (graphene); layers slide over each other.
• Properties:
  • • Black, soft, brittle, slippery, density 1.9–2.3 g/cm³.
    • Good conductor of electricity (free electrons in layers).
    • Does not dissolve in most solvents.
• Uses:
  • • Lubricants, pencils, carbon electrodes, paints, arc lamps (bright light).
• Activity:
  • • Rub pencil lead (graphite) → soft and slippery.
    • Test conductivity: Connect graphite in a circuit with a bulb → bulb glows (graphite conducts electricity).
    • Add graphite to water/kerosene → insoluble in both.

Fullerene:

• Found in: Soot, interstellar space (rare).
• Examples: C₆₀ (Buckminsterfullerene), C₇₀, C₈₂ (Nobel Prize 1996 to Kroto, Curl, Smalley).
• Structure: Buckyballs (C₆₀, spherical), buckytubes (tubes).

Properties:

• • 30–900 carbon atoms per molecule.
  • Soluble in organic solvents (e.g., carbon disulphide, chlorobenzene).

Uses:

• • Insulators, catalysts in water purification, superconductors at certain temperatures.

2. Non-Crystalline (Amorphous) Forms:

• Irregular arrangement of atoms.

Coal:

• Fossil fuel, contains C, H, O, N, P, S.
• Types:
  • Peat: <60% carbon, high water, low heat.
  • Lignite: 60–70% carbon (2nd stage).
  • Bituminous: 70–90% carbon (3rd stage).
  • Anthracite: ~95% carbon, hardest, purest.
• Uses:
  • Fuel (factories, homes), thermal power plants, produces coke, coal gas, coal tar.

Charcoal:

• Made from animal bones/horns or wood (burned with less air).
• Uses: Water purification, organic material purification.

Coke:

• Pure coal after removing coal gas.
• Uses: Domestic fuel, reducing agent, produces gases like water gas (CO + H₂).

Hydrocarbons

What Are Hydrocarbons?

• Basic organic compounds made of only carbon and hydrogen.
• Carbon (2,4) shares 4 electrons to complete its octet (like neon, 2,8) → forms covalent bonds.
• Example: Methane (CH₄) → 1 C shares electrons with 4 H atoms.

Properties of Covalent Compounds:

• Low melting/boiling points.
• Insoluble in water, soluble in organic solvents.
• Poor conductors of heat/electricity.

Types of Hydrocarbons:

• Saturated: Only single bonds between carbon atoms (e.g., ethane C₂H₆, propane C₃H₈).
• Unsaturated: At least one double or triple bond (e.g., ethene C₂H₄, ethyne C₂H₂, propene C₃H₆).

Solubility of Carbon:

• Activity: Add coal powder to water, kerosene, cooking oil → does not dissolve in any.
• Conclusion: Carbon is insoluble in water and organic solvents.

Carbon Dioxide (CO₂)

Molecular Formula: CO₂, Molecular Mass: 44, Melting Point: -56.6°C.

Occurrence:

• In air: 0.03%, exhaled air: 4%.
• As carbonates: Chalk, limestone (CaCO₃).
• Released during combustion of wood, coal.

Preparation (Activity):

• React CaCO₃ (limestone) with dilute HCl in a flask → CO₂ gas forms.
• Equation: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂.
• Collect CO₂ by upward displacement of air (denser than air).

Properties of CO₂:

Physical:

• Colorless, odorless gas.
• Slightly soluble in water (forms carbonic acid: CO₂ + H₂O → H₂CO₃).
• Denser than air.

Chemical:

• Turns moist blue litmus red (acidic due to H₂CO₃).
• Turns limewater milky: CO₂ + Ca(OH)₂ → CaCO₃ + H₂O.
• Universal indicator in CO₂ solution → orange/red (pH < 7, acidic).
• Extinguishes a burning candle (does not support combustion).
• Reacts with NaOH:
  • 2NaOH + CO₂ → Na₂CO₃ + H₂O (sodium carbonate).
  • Na₂CO₃ + H₂O + CO₂ → 2NaHCO₃ (sodium bicarbonate).

Uses of CO₂:

• Aerated drinks, cold storage (solid CO₂, dry ice), fire extinguishers.
• Solvent in eco-friendly dry cleaning, decaffeinating coffee.
• Plants use CO₂ for photosynthesis.
• Fire Extinguisher:
  • Contains NaHCO₃ and H₂SO₄ → 2NaHCO₃ + H₂SO₄ → Na₂SO₄ + 2H₂O + 2CO₂.
  • CO₂ is non-corrosive, non-conductive, used for electrical fires.

Methane (CH₄)

Molecular Formula: CH₄, Molecular Mass: 16.

Occurrence:

• Natural gas (87% methane), biogas, coal mines, marshy areas (called marsh gas).
• Formed by decomposition of organic matter without air (anaerobic).
• Made by heating H₂ and CO with nickel catalyst at 300°C.

Properties of CH₄:

Physical:

• Colorless gas, melting point: -182.5°C, boiling point: -161.5°C.
• Less dense than water, sparingly soluble in water, highly soluble in organic solvents.

Chemical:

• Burns in oxygen: CH₄ + 2O₂ → CO₂ + 2H₂O + heat (213 kcal/mol, bluish flame).
• Chlorination: CH₄ + Cl₂ → CH₃Cl + HCl (at 250–400°C with UV light).

Uses of CH₄:

• Fuel in industries (fabric mills, paper mills, food processing).
• Domestic fuel (less CO₂ emission).
• Produces ethanol, methyl chloride, acetylene.

Biogas Plant:

• Produces methane (55–60%) from animal dung, wet garbage (anaerobic decomposition).

Process:

1. Organic matter → organic acids.
2. Organic acids → CH₄ + CO₂ (by methanogenic bacteria).

Uses: Cooking gas, electricity generation; byproduct is good manure.

Eco-friendly: Reduces waste, renewable fuel.