Strong vs weak acids — it's about dissociation

5 minAS Level7.2.6

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By the end of this lesson

By the end you can explain the difference between strong and weak acids in terms of dissociation, define Ka and pKa, and compare conductivity, pH, and reaction rates for equal concentrations.

The key difference — dissociation

Strong acid: 100% dissociated in aqueous solution. $\text{HCl(aq)} \rightarrow \text{H}^+(\text{aq}) + \text{Cl}^-(\text{aq})$ (Single arrow — reaction goes to completion)

Weak acid: Partially dissociated — an equilibrium. $\text{CH}_3\text{COOH(aq)} \rightleftharpoons \text{H}^+(\text{aq}) + \text{CH}_3\text{COO}^-(\text{aq})$ (Equilibrium arrow — most molecules stay intact)

At 0.1 M: HCl gives [H⁺] = 0.1 M (pH 1.0). CH₃COOH gives [H⁺] ≈ 0.0013 M (pH 2.87).

Definition

Strong acid

An acid that is fully dissociated into ions in aqueous solution. Examples: HCl, HNO₃, H₂SO₄ (first proton only).

Definition

Weak acid

An acid that is partially dissociated in aqueous solution, establishing an equilibrium. Examples: CH₃COOH, H₂CO₃, NH₄⁺, HCOOH.

Strong or weak?

Multiple choiceQuestion 1 · Recall

Multiple choiceQuestion 2 · Recall

Answer the 2 questions above to continue.