Ch 4 explores organic chemistry — why carbon forms so many compounds, covalent bonding, hydrocarbons, functional groups, naming conventions, and important compounds like ethanol and ethanoic acid.
Carbon has 4 valence electrons → forms 4 covalent bonds (sharing electrons). This allows it to form chains, branches, and rings — explaining the huge number of carbon compounds. Allotropes: diamond (each C bonded to 4 others, hard), graphite (layers, conducts), fullerene (C₆₀ soccer ball).
Saturated hydrocarbons (alkanes): only single bonds, e.g., CH₄ (methane), C₂H₆ (ethane). Unsaturated: alkenes (C=C, e.g., C₂H₄ ethene) and alkynes (C≡C, e.g., C₂H₂ ethyne). Functional groups change properties: –OH (alcohol), –CHO (aldehyde), –COOH (carboxylic acid), –CO– (ketone). Homologous series: successive members differ by –CH₂–.
Ethanol (C₂H₅OH): used in beverages, fuel; reacts with Na to give H₂; dehydrated by H₂SO₄ to ethene. Ethanoic acid (CH₃COOH/vinegar): reacts with NaOH (neutralisation), Na₂CO₃ (gives CO₂), ethanol (esterification → ester). Soaps (sodium salt of long-chain fatty acid): micelle formation — hydrophobic tail traps oil, hydrophilic head dissolves in water.
Download: https://ncert.nic.in/textbook/pdf/jesc104.pdf | Complete book: https://ncert.nic.in/textbook/pdf/jesc1ps.zip
Hard water contains dissolved calcium/magnesium salts. Soap reacts with these to form an insoluble precipitate (scum) instead of lather: 2C₁₇H₃₅COONa + CaCl₂ → (C₁₇H₃₅COO)₂Ca↓ + 2NaCl. Detergents work in hard water because their calcium/magnesium salts are soluble.
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