pH Comparison of Strong vs. Weak Acids

Steps:

• Define strong acids as fully dissociating in water (e.g., H₂SO₄, HCl, HNO₃) and weak acids as partially dissociating (e.g., CH₃COOH).
• Calculate [H⁺] for equal concentrations: strong acids yield higher [H⁺] than weak acids.
• Evaluate option C: 0.1 mol/dm³ CH₃COOH (weak) has lower [H⁺] and thus higher pH than 0.1 mol/dm³ H₂SO₄ (strong, fully dissociates first H⁺).
• Eliminate others by checking definitions and properties.

Why C is correct:

• Weak acids like CH₃COOH dissociate partially (K_a ≈ 1.8 × 10^{-5}), yielding [H⁺] << 0.1 mol/dm³, so pH > 1; strong acids like H₂SO₄ fully dissociate, [H⁺] ≈ 0.1 mol/dm³, pH ≈ 1.

Why the others are wrong:

• A: Weak acids react with carbonates (produce CO₂), just slower than strong acids.
• B: Group 1 metal oxides (e.g., Na₂O) are basic, reacting with acids but not with bases (amphoteric = both).
• D: Both HCl and HNO₃ are strong monoprotic acids, so 0.1 mol/dm³ solutions have identical [H⁺] ≈ 0.1 mol/dm³ and pH ≈ 1.

Final answer: C