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General Science: Carbon and its Compounds
📅 Topic: General Science (Chemistry)
This chapter is a massive leap into Organic Chemistry. In competitive exams, this is a high-value chapter because it connects chemistry to biology, fuels, and industrial products. Questions often focus on Allotropes, Functional Groups, and the difference between Soaps and Detergents.
1. Why Carbon is Special (The "Versatile" Element)
Carbon forms millions of compounds, more than all other elements combined. Why?
- Catenation: The unique ability of Carbon to bond with other Carbon atoms to form long chains, branches, or rings.
- Tetravalency: Carbon has a valency of 4. It can bond with four other atoms.
- Small Size: The nucleus holds shared electrons strongly, making Carbon bonds very stable.
2. Bonding: The Covalent Bond
- Ionic Bond: Transfer of electrons (e.g., NaCl). Good conductors.
- Covalent Bond: Sharing of electrons. Properties: Low melting points, Poor conductors (no ions formed).
Types of Covalent Bonds:
- Single: Sharing 1 pair (e.g., Methane CH4).
- Double: Sharing 2 pairs (e.g., Oxygen O=O).
- Triple: Sharing 3 pairs (e.g., Nitrogen N≡N).
3. Allotropes of Carbon
Forms of pure Carbon. Memorize the differences as this is a favorite comparison question.
- Diamond:
- Structure: 3D rigid network.
- Hardness: Hardest natural substance.
- Conductivity: Insulator (No free electrons).
- Graphite:
- Structure: Hexagonal layers.
- Hardness: Soft and Slippery (layers slide). Used as lubricant.
- Conductivity: Good Conductor (One free electron per carbon).
- Fullerene (C-60):
- Structure: Football shape (Geodesic dome). Used in Nanotechnology.
4. Hydrocarbons (Compounds of C and H)
A. Saturated (Alkanes)
Bonding: Only Single bonds.
Reactivity: Less reactive (clean fuel).
Flame: Burns with a Blue (Clean) flame.
Formula: CnH2n+2.
B. Unsaturated (Alkenes & Alkynes)
Bonding: Double or Triple bonds.
Reactivity: More reactive.
Flame: Burns with a Yellow (Sooty) flame.
Test: They decolorize Bromine Water (Red-brown → Colorless).
C. Isomers
Compounds with the Same Molecular Formula but Different Structures.
Example: Butane (C4H10) can be a straight chain or branched.
5. Important Carbon Compounds
A. Ethanol (Ethyl Alcohol - C2H5OH)
- Uses: Alcoholic drinks, Solvent (Tincture Iodine), Cough syrups.
- Reaction with Sodium: Releases Hydrogen Gas.
- Dehydration: Heating with Conc. H2SO4 removes water → forms Ethene.
B. Ethanoic Acid (Acetic Acid - CH3COOH)
- Vinegar: 5-8% solution of Acetic Acid in water.
- Glacial Acetic Acid: Pure acid freezes at 290K (looks like ice).
- Esterification: Reacts with Alcohol → Ester (Sweet smelling substance used in perfumes).
- With Carbonates: Releases CO2 (Turns lime water milky).
6. Soaps and Detergents
A. Soap
Definition: Sodium or Potassium salt of long-chain carboxylic acid.
Mechanism (Micelles):
- Hydrophilic Head: Loves water.
- Hydrophobic Tail: Loves oil/dirt.
- Action: The tail attaches to oily dirt, the head stays in water, forming a cluster called a Micelle.
Soap does not work in Hard Water because Calcium/Magnesium ions react with soap to form an insoluble white precipitate called Scum.
B. Detergents
Definition: Sodium salts of sulphonic acids.
Advantage: Works in Hard Water (does not form scum). Used in shampoos.
7. Mentor’s Final Drill (Exam-Ready Questions)
A: Graphite.
Q: What is the gas responsible for the "fizz" when Baking Soda reacts with Vinegar?
A: Carbon Dioxide (CO2).
Q: Why does the bottom of a cooking vessel turn black?
A: Incomplete combustion of fuel (blocked air holes), creating soot.
Q: What is the chemical reaction used to convert vegetable oil into vegetable ghee (Vanaspati)?
A: Hydrogenation (Addition Reaction) using a Nickel catalyst.
Q: What is "Denatured Alcohol"?
A: Ethanol mixed with poisonous Methanol to prevent misuse (drinking).
Action Plan: Focus on the differences between Soap and Detergent and the properties of Ethanol. These are very practical topics and examiners love them. You have now covered the "Big 4" chemistry chapters. Keep pushing!