What is an acid?
An acid is a substance that produces hydrogen ions (H⁺) when dissolved in aqueous solution.
Acid Strength
Acid strength refers to how easily an acid dissociates into ions when dissolved in water.
Strong acid
A strong acid undergoes complete dissociation to form ions in water.
In a solution of a strong acid, all molecules dissociate to become H⁺ ions and anions.
Examples include Nitric acid (HNO3), Hydrochloric acid (HCl) and Sulfuric acid (H2SO4)
Ionic Equations:
- Hydrochloric acid: HCl(aq) → H⁺(aq) + Cl⁻(aq)
- Nitric acid: HNO₃(aq) → H⁺(aq) + NO₃⁻(aq)
- Sulfuric acid: H₂SO₄(aq) → 2H⁺(aq) + SO₄²⁻(aq)
Weak acid
A weak acid undergoes partial dissociation in water.
Only a small number of acid molecules dissociate to form H⁺ ions.
Examples include Ethanoic acid/Acetic acid (CH3COOH ) and Citric acid (C6H8O7 )
Ionic Equations:
- Ethanoic acid (Acetic acid): CH₃COOH(aq) ⇌ H⁺(aq) + CH₃COO⁻(aq)
- Citric acid: C₆H₈O₇(aq) ⇌ H⁺(aq) + C₆H₇O₇⁻(aq)
(Note the reversible arrow ⇌ showing partial dissociation)
| Property | Strong Acids | Weak Acids |
|---|---|---|
| Dissociation in water | Complete | Partial |
| H⁺ ion concentration | High | Low |
| Typical pH | 0 – 3 | 4 – 6 |
| Electrical conductivity | High | Low |
| Common examples | HCl, HNO₃, H₂SO₄ | CH₃COOH, citric acid |
Key Summary
- Strong acids → Completely ionised in water → High concentration of H⁺ ions
- Weak acids → Partially ionised in water → Low concentration of H⁺ ions
- Both strong and weak acids can have the same concentration, but strong acids are much more reactive, conduct electricity better, and have lower pH values.
Science with Tara 