The Four Types
| Titration | Start pH | Equiv. Pt pH | Sharp Jump? |
|---|---|---|---|
| SA+SB | ~1 | = 7 | Very sharp |
| WA+SB | ~3 | > 7 | Moderate |
| SA+WB | ~1 | < 7 | Moderate |
| WA+WB | ~3 | ≈ 7 | Gradual |
pH Titration Curves (Adding Strong/Weak Base to Acid)
HL Extension
Half-Equivalence Point: pH = pKa
At the half-equivalence point (\(V = \frac{1}{2}V_{\text{eq}}\)) in a weak acid-strong base titration:
\[[\text{HA}] = [\text{A}^-] \implies \textbf{pH = pK}_\text{a}\]This provides a direct experimental method for determining \(K_{\text{a}}\) or \(K_{\text{b}}\) from titration curves.
Examiner Trap
Equivalence Point pH vs Titration Type
- Buffer Region: Present only in weak acid + strong base (or weak base + strong acid) titrations around the half-equivalence point.
- Equivalence Point pH:
• Strong + Strong: \(\text{pH} = 7\)
• Weak Acid + Strong Base: \(\text{pH} > 7\) (basic salt hydrolysis)
• Strong Acid + Weak Base: \(\text{pH} < 7\) (acidic salt hydrolysis)
• Weak + Weak: No sharp inflection jump!
AQA GCSE & IB Chemistry
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