Oxygen is more electronegative than sulphur, yet is acidic in nature while is neutral because: — p Block Elements Chemistry Question

💡 Solution & Explanation

# Why $H_2S$ is Acidic While $H_2O$ is Neutral **Step 1: Understand the acid dissociation requirement** For a hydride to be acidic, it must readily release $H^+$ ions. This depends on: - Bond strength (weaker bonds dissociate more easily) - Stability of the conjugate base **Step 2: Compare bond strengths** - $H-O$ bond: **467 kJ/mol** (very strong) - $H-S$ bond: **366 kJ/mol** (significantly weaker) The $H-S$ bond is much weaker because sulfur is larger than oxygen. In larger atoms, the orbital overlap with hydrogen is poorer, creating a weaker bond. **Step 3: Analyze conjugate base stability** - Conjugate base of $H_2O$: $OH^-$ (very stable due to high charge density on small O atom) - Conjugate base of $H_2S$: $HS^-$ (less stable because charge is dispersed over larger S atom) **Step 4: Apply equilibrium reasoning** Although oxygen is more electronegative (pulling electron density toward itself), the **weak $H-S$ bond overcomes this effect**. The dissociation equilibrium favors ionization: $$H_2S \rightleftharpoons H^+ + HS^- \quad \text{(more favorable)}$$ $$H_2O \rightleftharpoons H^+ + OH^- \quad \text{(less favorable)}$$ **Conclusion:** Bond strength is the dominant factor here. The weaker $H-S$ bond makes $H_2S$ acidic, while the strong $H-O$ bond keeps $H_2O$ neutral, despite oxygen's higher electronegativity. *Answer C states this reasoning correctly.*