Ph At Equivalence Of A Titration Calculator

Equivalence Point pH Formula:

\[ \text{pH} = -\log\left(\sqrt{\frac{K_w \times K_a}{K_b}}\right) \]

Acid Type:

Base Type:

Acid Dissociation Constant (Ka):

(mol/L)

Base Dissociation Constant (Kb):

(mol/L)

Equivalence Point pH:

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1. What is Equivalence Point pH?

The equivalence point pH in a titration is the pH at which the amount of titrant added is stoichiometrically equal to the amount of analyte present in the sample. It's a crucial point in acid-base titrations that helps determine the concentration of the unknown solution.

2. How Does the Calculator Work?

The calculator uses different formulas based on the strength of the acid and base:

Weak Acid + Strong Base: \[ \text{pH} = -\log\left(\sqrt{K_w \times K_a}\right) \]

Strong Acid + Weak Base: \[ \text{pH} = 14 + \log\left(\sqrt{K_w \times K_b}\right) \]

Weak Acid + Weak Base: \[ \text{pH} = -\log\left(\sqrt{\frac{K_w \times K_a}{K_b}}\right) \]

Strong Acid + Strong Base: pH = 7 (neutral)

Where:

\( K_w \) — Water dissociation constant (1.0 × 10⁻¹⁴ at 25°C)
\( K_a \) — Acid dissociation constant
\( K_b \) — Base dissociation constant

3. Importance of Equivalence Point pH

Details: Knowing the equivalence point pH is essential for selecting appropriate indicators in titrations and understanding the nature of the resulting solution after neutralization.

4. Using the Calculator

Tips: Select whether your acid and base are strong or weak, then enter their dissociation constants (Ka and Kb). For strong acids/bases, you can enter very small values (like 1e-14) since they completely dissociate.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between equivalence point and endpoint?
A: Equivalence point is when stoichiometric amounts have reacted, while endpoint is when the indicator changes color (they should be close but may differ slightly).

Q2: How do I find Ka and Kb values?
A: These are typically found in chemistry reference tables or can be determined experimentally.

Q3: Why is the pH not 7 for all equivalence points?
A: Only strong acid-strong base titrations give neutral pH 7. Weak acids/bases produce solutions with pH determined by their conjugate bases/acids.

Q4: Does temperature affect the equivalence point pH?
A: Yes, because Kw changes with temperature. This calculator assumes standard conditions (25°C).

Q5: Can I use this for polyprotic acids?
A: This calculator is for monoprotic systems. Polyprotic acids have multiple equivalence points with different calculations.