Mono- and polyprotic acids

Classification of Acids by Proton Donation

Acids can be classified based on the number of protons $(H⁺)$ they can donate:

• Monoprotic acids donate only one proton $(H⁺).$
• Polyprotic acids donate two or more protons in steps.

1. Monoprotic Acids

• Can only donate one proton $(H⁺)$ per molecule.
• Examples:
  • Hydrochloric acid $(HCl) → HCl → H⁺ + Cl⁻$
  • Nitric acid $(HNO₃)$
  • Ethanoic acid $(CH₃COOH)$

2. Polyprotic Acids

Polyprotic acids release more than one proton in stages.

a) Diprotic Acids (Donate 2 Protons)

• Example: Sulphuric acid $(H₂SO₄)$
  • Step 1: $H₂SO₄ → H⁺ + HSO₄⁻$
  • Step 2: $HSO₄⁻ → H⁺ + SO₄²⁻$
• Other Example: Carbonic acid $(H₂CO₃)$

b) Triprotic Acids (Donate 3 Protons)

• Example: Phosphoric acid $(H₃PO₄)$
  • Step 1: $H₃PO₄ → H⁺ + H₂PO₄⁻$
  • Step 2: $H₂PO₄⁻ → H⁺ + HPO₄²⁻$
  • Step 3: $HPO₄²⁻ → H⁺ + PO₄³⁻$

Summary

Type	Protons Donated $(H⁺)$	Examples
Monoprotic	1	$HCl, HNO₃, CH₃COOH$
Diprotic	2	$H₂SO₄, H₂CO₃$
Triprotic	3	$H₃PO₄$

Key Points:

• Stronger acids ionise completely in water, releasing all their $H⁺$ ions.
• Weaker acids partially ionise, meaning not all $H⁺$ are released at once.
• Polyprotic acids release protons in steps, making them behave differently in reactions.