Acids, Bases, and Salts: pH scale ranges 0-14. pH < 7 = acidic, pH = 7 = neutral, pH > 7 = basic/alkaline. Common indicators and their colors: Litmus (red in acid, blue in base), Phenolphthalein (colorless in acid, PINK in base — not red), Methyl Orange (red/orange in acid, yellow in base), Universal indicator (shows full pH spectrum). Human blood pH: 7.35-7.45 (slightly alkaline). Gastric juice pH: ~2 (highly acidic).

Important chemical compounds and formulas (match-the-following favorite): Baking Soda — NaHCO₃ (Sodium Bicarbonate), Washing Soda — Na₂CO₃.10H₂O (Sodium Carbonate decahydrate), Bleaching Powder — Ca(OCl)₂ / CaOCl₂ (Calcium Hypochlorite), Plaster of Paris — CaSO₄.½H₂O (Calcium Sulphate hemihydrate), Quick Lime — CaO (Calcium Oxide), Slaked Lime — Ca(OH)₂ (Calcium Hydroxide), Common Salt — NaCl, Blue Vitriol — CuSO₄.5H₂O.

Colloids: Particles are larger than molecules but too small for the naked eye (1-1000 nm). They scatter light (Tyndall Effect — path of light becomes visible). KEY FACT: Colloids are HETEROGENEOUS mixtures (not homogeneous — this is the most common REET chemistry trick!). Examples: milk (liquid-liquid), fog (liquid-gas), smoke (solid-gas), blood, ink, gelatin. Colloid components: Dispersed phase (scattered particles) and Dispersion medium (substance in which particles are scattered).

Chemical reactions: Combination (A + B → AB), Decomposition (AB → A + B), Displacement (A + BC → AC + B), Double Displacement (AB + CD → AD + CB), Redox (oxidation + reduction simultaneously). Rusting = iron + oxygen + moisture (slow oxidation). Rancidity = oxidation of fats/oils in food (prevented by antioxidants, nitrogen packing, refrigeration). Corrosion = gradual destruction of metals by chemical reaction with environment.

Carbon and its compounds: Carbon has 4 valence electrons, forms covalent bonds. Allotropes: Diamond (hardest natural substance, each C bonded to 4 others), Graphite (soft, conducts electricity, each C bonded to 3 others with delocalized electrons), Fullerene (C₆₀, Buckminsterfullerene). Hydrocarbons: Saturated (single bonds, alkanes — CₙH₂ₙ₊₂) and Unsaturated (double/triple bonds, alkenes CₙH₂ₙ, alkynes CₙH₂ₙ₋₂). Ethanol (C₂H₅OH) and Ethanoic acid (CH₃COOH) are important organic compounds.

REET Exam Tips: 9 questions. Focus on: pH values (blood, gastric juice), indicator colors (phenolphthalein = PINK not red in base), compound-formula matching, colloids = HETEROGENEOUS (not homogeneous — trap!), and chemical reaction types. Assertion-Reason format tests subtle distinctions.