1. What is Polyprotic Acid Titration?

Polyprotic acid titration involves acids that can donate more than one proton (e.g., H₂SO₄, H₃PO₄). The intermediate equivalence point pH is approximately the average of the two relevant pKa values.

2. How Does the Calculator Work?

The calculator uses the polyprotic acid titration formula:

Where:

• \( pKa_1 \) — First acid dissociation constant
• \( pKa_2 \) — Second acid dissociation constant
• \( pH \) — Resulting pH value at intermediate equivalence point

Explanation: This approximation holds when the equivalence point is between the first and second proton dissociations for diprotic acids.

3. Importance of pH Calculation

Details: Accurate pH estimation is crucial for understanding acid-base equilibria, buffer capacity, and predicting titration curves in analytical chemistry.

4. Using the Calculator

Tips: Enter both pKa values as dimensionless numbers. The calculator will compute the approximate pH at the intermediate equivalence point.

5. Frequently Asked Questions (FAQ)

Q1: What types of acids does this apply to?
A: This applies to diprotic acids like H₂SO₄, H₂CO₃, and the first two dissociations of triprotic acids like H₃PO₄.

Q2: When is this approximation valid?
A: This approximation works best when pKa values are sufficiently separated (typically ΔpKa > 2-3 units).

Q3: What are typical pKa values?
A: For H₂SO₄: pKa₁ ≈ -3, pKa₂ ≈ 1.9; For H₃PO₄: pKa₁ ≈ 2.1, pKa₂ ≈ 7.2, pKa₃ ≈ 12.3.

Q4: Are there limitations to this equation?
A: This is an approximation that assumes ideal behavior and may need adjustment for concentrated solutions or when pKa values are very close.

Q5: Can this be used for triprotic acids?
A: Yes, for the intermediate equivalence point between first and second dissociations, or second and third dissociations with appropriate pKa values.