1. What is the pH Calculation at Equivalence Point?

This calculator determines the pH at the equivalence point in a weak acid-strong base titration using the formula: pH = ½ pKw + ½ pKa + ½ log C. This represents the hydrolysis of the conjugate base formed at the equivalence point.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( pH \) — pH value (dimensionless)
• \( pK_w \) — Water ionization constant (dimensionless, typically 14.00)
• \( pK_a \) — Acid dissociation constant (dimensionless)
• \( C \) — Concentration of salt formed at equivalence point (mol/L)

Explanation: At the equivalence point of a weak acid-strong base titration, the solution contains the conjugate base of the weak acid, which hydrolyzes to produce a basic solution.

3. Importance of pH Calculation

Details: Calculating the pH at the equivalence point is crucial for understanding titration curves, selecting appropriate indicators, and determining the exact endpoint of acid-base titrations.

4. Using the Calculator

Tips: Enter pKa of the weak acid, pKw (typically 14.00 at 25°C), and concentration C of the salt formed. All values must be valid positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: Why is the pH >7 at equivalence point?
A: Because the conjugate base of a weak acid hydrolyzes water, producing OH⁻ ions and creating a basic solution.

Q2: What is the typical pKw value?
A: pKw is 14.00 at 25°C, but it varies with temperature. Use appropriate values for different temperatures.

Q3: How is concentration C determined?
A: C is the concentration of the salt formed at equivalence point, calculated from the initial concentrations of acid and base.

Q4: Does this formula work for all weak acids?
A: Yes, this formula applies to all weak acid-strong base titrations at the equivalence point.

Q5: What if the concentration is very dilute?
A: For very dilute solutions, additional corrections may be needed as the approximation becomes less accurate.