Topic 1 · 33.1 i–iii · Free
Topic Notes · Easy summaries with diagrams
Chapter 33 — Chapter 33 — Water
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📘Easy summary
Water is the foundation of life: hydration, hygiene, photosynthesis, agriculture, climate balance and ecosystems. H₂O is a permanent dipole; this polarity gives unique properties. (i) Thermal stability: hydrogen bonding gives high specific heat capacity and high heat of vaporisation, so large water bodies resist rapid temperature changes. (ii) Unique solvent: dissolves ionic substances (metal ions, NO₃⁻, PO₄³⁻) by surrounding the ions; it also dissolves polar organic compounds, so many pesticides and herbicides enter the water cycle, persist and bioaccumulate. (iii) Amphoteric nature: acts as acid and base; self-ionisation Kw = 1.0 × 10⁻¹⁴ at 25 °C is the baseline of the pH scale. Aquatic life is sensitive to pH; acid rain (SO₂, NOx) raises H₃O⁺, which mobilises toxic metals (aluminium hydroxide, lead salts) from sediments by protonation or displacement.
⭐Key points
- Permanent dipole → H-bonds.
- High specific heat → thermal stability.
- Good solvent for ions and polar organics.
- Kw = 1.0 × 10⁻¹⁴; acid mobilises metals.
🔬Diagram
🌿Real-life example
Lakes stay cooler than land on hot days due to high specific heat.
💡Exam tip
- Link each property back to polarity/H-bonding.
✅Quick check
1. Water resists temperature change due to:
2. Kw at 25 °C:
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