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Strong Acids and Strong Bases

Chemistry

1. Fundamental Concepts

Strong Acids

  • Dissociate completely (≈100%) in aqueous solution

  • Each molecule releases H⁺ (or H₃O⁺)

  • Classified as strong electrolytes

Strong Bases

    • Dissociate completely in water

    • Produce OH⁻ ions

    • Typically metal hydroxides

2. Key Concepts

Common Strong Acids (Must Memorize)

Strong Acid Name
HCl Hydrochloric acid
HBr Hydrobromic acid
HI Hydroiodic acid
HNO₃ Nitric acid
H₂SO₄ First H⁺ fully dissociates
HClO₄ Perchloric acid

📌 Common mnemonic:
“So I Brought No Clean Clothes”

Common Strong Bases

Strong Base Notes
LiOH, NaOH, KOH Alkali metal hydroxides
Ca(OH)₂, Sr(OH)₂, Ba(OH)₂ Alkaline earth metal hydroxides

⚠️ Notes:

  • NH₃ is a weak base

  • Mg(OH)₂ has low solubility and is usually not treated as a strong base

pH Characteristics

  • Strong acids: pH ≈ 0–3

  • Strong bases: pH ≈ 11–14

  • For strong acids/bases:

    [H+]≈acid molarity,[OH−]≈base molarity[\text{H}^+] \approx \text{acid molarity},\quad [\text{OH}^-] \approx \text{base molarity}

3. Examples

Easy

Which of the following is a strong acid?
A. CH₃COOH
B. HF
C. HCl
D. H₂CO₃

Answer: C
HCl dissociates completely in water.

Medium

What is the [OH⁻] of a 0.020 M NaOH solution?

NaOH is a strong base and dissociates completely:

[OH−]=0.020 M[\text{OH}^-] = 0.020\ \text{M}

Answer: 0.020 M

Hard

Calculate the pH of 0.0050 M HNO₃

HNO₃ is a strong acid:

[H+]=0.0050 M[\text{H}^+] = 0.0050\ \text{M} pH=−log⁡(0.0050)≈2.30

Answer: pH ≈ 2.30

4. Problem-Solving Techniques

  • Identify: strong acid or strong base → complete dissociation.
  • Calculate or .
  • For mixtures: calculate moles, determine which is in excess.
  • Use excess ion concentration to find pH or pOH.
  • Remember: pH = -log, pH + pOH = 14.
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