The Acid Race: HCl vs Ethanoic Acid
Same concentration. Wildly different speeds. Why?
🕵️ The Detective's Puzzle
You're a lab technician. Two bottles sit on the bench: 1.0 mol/dm³ HCl and 1.0 mol/dm³ Ethanoic Acid. Same concentration label. You drop identical strips of magnesium into both.
Beaker A (HCl)
Violent fizzing. Mg disappears in seconds.
Beaker B (Ethanoic)
Slow, lazy bubbles. Mg dissolves gradually.
🤔 The Question That Should Bother You:
If both are 1.0 mol/dm³, why does one react 10× faster?
⚡ The Secret: Strong vs Weak
HCl — The STRONG Acid
HCl completely dissociates in water. Every single molecule donates its H⁺.
1.0 mol/dm³ HCl → 1.0 mol/dm³ H⁺ ✓
CH₃COOH — The WEAK Acid
Ethanoic acid only partially dissociates. Only ~1% of molecules release H⁺. The rest stay intact.
1.0 mol/dm³ CH₃COOH → ~0.01 mol/dm³ H⁺ ⚠️
🎯 The Collision Theory Link
Magnesium reacts with H⁺ ions, not the acid molecule itself.
HCl has 100× more free H⁺ than ethanoic acid at the same concentration.
More H⁺ → more frequent collisions with Mg → faster rate.
⚠️ SAFETY NOTE
HCl is corrosive. Wear goggles and gloves. H₂ gas produced is flammable — no naked flames near the experiment.
Sign In to Keep Going
You've reached the end of the free preview. Sign in — and upgrade to Plus or Pro — to keep going with Chemistry.
Full Access
Unlock all 320 lessons