Q.10 Water can dissolve many organic molecules due to
1. Dipolar character and ability to form hydrogen bond
2. Hydrophilic character and high conductance
3. Amphiphilic character and high insultation capacity
4. Hydrophobic character and ability to fonn disulfide bond
Correct Answer: Option 1
Water dissolves many organic molecules primarily due to its dipolar nature and hydrogen bonding capacity, which interact with polar functional groups like -OH and -NH₂ in solutes such as alcohols, sugars, and amines.
Option Analysis
Option 1: Correct
Water’s polarity (bent molecule, partial charges on O/H) enables dipole-dipole interactions and hydrogen bonding with organic molecules bearing electronegative atoms (O, N). This solvation shell stabilizes polar solutes like glucose or ethanol, overcoming lattice energy.
Option 2: Incorrect
Hydrophilic character describes water-loving solutes, not water itself; high conductance relates to ions (e.g., salts), irrelevant for neutral organics like methanol, which dissolve via H-bonding without conductivity.
Option 3: Incorrect
Amphiphilic refers to dual hydrophilic/hydrophobic molecules (e.g., surfactants); water lacks this and has no notable insulation capacity—it’s a conductor for ions.
Option 4: Incorrect
Hydrophobic means water-repelling, opposite of water’s solvent role; disulfide bonds (-S-S-) form in proteins via cysteine oxidation, unrelated to solubility.
Introduction to Water Solubility
Water can dissolve many organic molecules due to its dipolar character and ability to form hydrogen bonds, a core concept in biochemistry for exams like GATE Life Sciences. This property explains why polar organics like ethanol mix freely while hydrocarbons do not.
Key Solubility Mechanism
Water’s dipole (μ ≈ 1.85 D) and H-bonding (as donor/acceptor) surround polar groups, e.g., -OH in glucose forms multiple H-bonds.
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“Like dissolves like”: Polar organics soluble up to ~4-5 C atoms per polar group.
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Examples: Methanol (infinite solubility), butanol (limited).
Solubility Rules Comparison
| Property | Water’s Role | Effect on Organics |
|---|---|---|
| Dipolar/H-bonding | Solvation shell | High solubility (alcohols, amines) |
| Hydrophilic | Solute trait | Not water’s property |
| Amphiphilic | Surfactants | Forms micelles, not dissolution |
| Hydrophobic | Hydrocarbons | Insoluble (e.g., hexane) |
This confirms option 1 as the correct reason water dissolves organic molecules.
Exam Tips for Life Sciences
Memorize: H-bonding > chain length for solubility. Avoid traps like conductance (ionic) or disulfides (covalent). Practice with glucose vs. cholesterol.
