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Topic Notes · Easy summaries with diagrams
Chapter 20 — Chapter 20 — Water
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📘Easy summary
Natural water contains dissolved gases (O₂, N₂, CO₂ from the atmosphere by diffusion), dissolved salts/minerals (Ca²⁺, Mg²⁺, useful in small amounts), and harmful substances: microbes (from human and animal wastes/sewage), fertilizers, pesticides, heavy metals (Pb, Hg, As), industrial waste, plastics. Tap water contains dissolved salts, gases and chlorine; distilled water is pure H₂O. Purity tests: pure water boils at exactly 100 °C and freezes at 0 °C (at 1 atm); pH 7; anhydrous CuSO₄ (white → blue) or cobalt chloride (blue → pink) detect water.
⭐Key points
- pH of pure water = 7.
🔬Diagram
🌿Real-life example
Fish breathe dissolved O₂.
💡Exam tip
- Pure: b.p. 100 °C.
✅Quick check
1. pH distilled water:
2. Microbes source:
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