UPSC Prelims 2021 Q71: Science & Technology – Chemistry
- (a) it is dipolar in nature
- (b) it is a good conductor of heat
- (c) it has high value of specific heat
- (d) it is an oxide of hydrogen
Answer: (a) it is dipolar in nature
Explanation
Why Water is the Universal Solvent
| Property | Explains Solvent Power? | Detail |
|---|---|---|
| Dipolar (polar) nature | YES - PRIMARY REASON | Water molecules have a bent shape with oxygen (partially negative) and hydrogen (partially positive) creating a dipole. This polarity allows water to dissolve ionic compounds (Na+/Cl-) and polar molecules by surrounding them with oppositely charged ends (hydration shells). |
| Good heat conductor | NO | Thermal conductivity does not determine solvent ability. |
| High specific heat | NO | Affects temperature stability, not dissolution capacity. |
| Oxide of hydrogen | NO | Chemical composition alone doesn't explain solvent behaviour - polarity does. |
Answer: (a) it is dipolar in nature.
Water's polarity comes from oxygen's higher electronegativity (3.44) vs hydrogen (2.20), creating partial charges that enable water to solvate ions and polar molecules through hydrogen bonding and dipole-ion interactions.
Why each option is right or wrong
- (a) CORRECT. Water dissolves more substances than any other liquid because it is DIPOLAR (polar). Oxygen is partially negative; hydrogens are partially positive. This lets water surround and dissolve ionic and polar substances via hydration shells.
- (b) Incorrect. Heat conductivity doesn't determine solvent ability.
- (c) Incorrect. High specific heat is about temperature stability, not dissolution.
- (d) Incorrect. Being an oxide of hydrogen is a compositional fact, not a functional explanation for solvent behaviour.
Key point
Water = universal solvent because of its DIPOLAR (polar) nature. Oxygen partial negative + Hydrogen partial positive = dipole. Dissolves ionic compounds (Na+/Cl-) by forming hydration shells. Also dissolves polar molecules via H-bonding.
Remember
Water can dissolve more substances than any other liquid because it is DIPOLAR in nature - oxygen carries a partial negative charge, hydrogens carry partial positive charges. This lets water surround and dissolve ionic and polar substances via hydration shells and hydrogen bonding. Correct answer: (a).
Common mistakes
- Confusing water's various unique properties (high SH, high boiling point, ice-floats, universal solvent). ONLY polarity explains solvent ability.
- Not knowing water is 'universal solvent' only for polar/ionic substances - NOT for non-polar substances (oil, wax).
- Missing water's other unique properties: cohesion (surface tension), adhesion (capillary action), high heat of vaporisation (sweating cools body).
Exam tip
Water's polarity explains: (i) solvent power (dissolves ionic + polar), (ii) hydration shell formation, (iii) hydrogen bonding, (iv) high boiling point (100C), (v) high surface tension, (vi) cohesion + adhesion. All flow from the same dipole property.
Sources
- NCERT Class IX Science - Chapter on Matter in Our Surroundings
- NCERT Class XI Chemistry - Chapter on Hydrogen and Its Compounds