pH of a strong acid and a weak acid
"pH of a strong acid and a weak acid" is a free, interactive Class 11 Chemistry simulation for NEET and JEE, built on the lesson "Ionisation of water, pH, weak acids and weak bases" in Equilibrium. HCl gives up every proton; acetic acid (vinegar's acid) gives up only a few. Slide the concentration, switch acids, and watch the indicator colour and the pH. For a strong acid pH = −log C; each tenfold dilution adds 1, and near 10⁻⁶ M water's own H⁺ takes over, so the pH creeps towards 7 but never passes it. For a weak acid [H⁺] ≈ √(Ka·C): a tenfold dilution adds only about 0.5, because α, the fraction ionised, grows as the acid gets more dilute. JEE Main asked 52 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
From the lesson Ionisation of water, pH, weak acids and weak bases in Equilibrium. Change the values and watch what happens.
In JEE Main
42 shifts analysed
52 questions from Equilibrium across the 42 JEE Main shifts Lumi has analysed (2017–2026).
The idea behind it
NCERT § "Ionization of Acids and Bases"
- Water self-ionises: its ionic product Kw = [H₃O⁺][OH⁻] = 1.0 × 10⁻¹⁴ at 298 K, so pure water there has [H₃O⁺] = 1.0 × 10⁻⁷ M and pH 7.
- Kw increases with temperature, so neutral water has pH below 7 when hot; neutrality means [H₃O⁺] = [OH⁻], not pH = 7.
- pH = −log[H₃O⁺] and pH + pOH = pKw = 14 at 298 K.
- For strong acids and bases, take complete dissociation and count all H⁺ or OH⁻ released: 0.05 M Ba(OH)₂ gives [OH⁻] = 0.10 M, pOH 1 and pH 13.
- For a weak acid HA of concentration c and degree of ionisation α, Ka = cα²/(1 − α); when α is small, α ≈ √(Ka/c) and [H₃O⁺] ≈ √(Ka c).
- pKa = −log Ka; a larger Ka (smaller pKa) means a stronger acid. Weak bases are treated the same way with Kb.
- For a conjugate pair, Ka × Kb = Kw, so pKa + pKb = 14 at 298 K.
- Polyprotic acids ionise in steps with Ka₁ > Ka₂ > Ka₃, because removing a proton from a negative ion is harder.
- Acid strength of H–A: down a group, bond strength controls it (HF < HCl < HBr < HI); along a period, electronegativity of A controls it (CH₄ < NH₃ < H₂O < HF).
Questions
3 answers
- What does the "pH of a strong acid and a weak acid" simulation show?
- HCl gives up every proton; acetic acid (vinegar's acid) gives up only a few. Slide the concentration, switch acids, and watch the indicator colour and the pH.
- Does JEE Main ask questions from Equilibrium?
- Yes. JEE Main asked 52 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
- Is this simulation free?
- Yes. It is free and runs in the browser on a phone or a laptop. It belongs to the lesson "Ionisation of water, pH, weak acids and weak bases" in Equilibrium (Class 11 Chemistry).
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