Ch 2 covers the chemistry of acids, bases, and salts — their properties, reactions, the pH scale, and important salts used in daily life like common salt, baking soda, washing soda, and plaster of Paris.
Acids taste sour, turn blue litmus red, produce H⁺ ions in water. Bases taste bitter, feel soapy, turn red litmus blue, produce OH⁻ ions. Strong acids: HCl, H₂SO₄, HNO₃. Strong bases: NaOH, KOH. Indicators: litmus, methyl orange, phenolphthalein, turmeric. pH scale: 0–14 (< 7 acidic, = 7 neutral, > 7 basic).
Acid + Metal → Salt + H₂ (Zn + 2HCl → ZnCl₂ + H₂↑). Acid + Metal carbonate → Salt + H₂O + CO₂↑. Acid + Base → Salt + Water (neutralisation). Acid + Metal oxide → Salt + Water. Base + Non-metal oxide → Salt + Water.
Common salt (NaCl): electrolysis gives NaOH + Cl₂ + H₂ (chlor-alkali process). Baking soda (NaHCO₃): antacids, fire extinguishers, baking. Washing soda (Na₂CO₃·10H₂O): cleaning, softening water. Plaster of Paris (CaSO₄·½H₂O): casts, moulds, decoration. Bleaching powder (CaOCl₂): disinfection, bleaching.
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The stomach produces hydrochloric acid (HCl) to create an acidic environment (pH ~1.2) needed for the enzyme pepsin to digest proteins. HCl also kills bacteria that enter with food. When excess acid is produced, it causes acidity/heartburn, treated with antacids (mild bases like NaHCO₃ or Mg(OH)₂).
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