Calculating Ph Of Buffer After Adding Acid

Buffer pH Equation After Acid Addition:

\[ pH_{new} = pKa + \log\left( \frac{[A⁻] - added}{[HA] + added} \right) \]

pKa:

dimensionless

[A⁻] (Conjugate Base):

mol

[HA] (Weak Acid):

mol

Added Acid:

mol

New pH:

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1. What is the Buffer pH Equation After Acid Addition?

The buffer pH equation after acid addition calculates the new pH of a buffer solution when a strong acid is added. It is derived from the Henderson-Hasselbalch equation and accounts for the consumption of conjugate base and formation of more weak acid.

2. How Does the Calculator Work?

The calculator uses the buffer pH equation after acid addition:

\[ pH_{new} = pKa + \log\left( \frac{[A⁻] - added}{[HA] + added} \right) \]

Where:

\( pKa \) — Acid dissociation constant (dimensionless)
\( [A⁻] \) — Initial concentration of conjugate base (mol)
\( [HA] \) — Initial concentration of weak acid (mol)
\( added \) — Amount of strong acid added (mol)

Explanation: The equation shows how the pH changes when strong acid is added to a buffer system, converting some conjugate base to weak acid.

3. Importance of Buffer pH Calculation

Details: Accurate pH calculation is crucial for understanding buffer capacity, predicting pH changes in chemical and biological systems, and designing effective buffer solutions for laboratory and industrial applications.

4. Using the Calculator

Tips: Enter pKa value, initial concentrations of conjugate base and weak acid in moles, and the amount of acid added in moles. All values must be valid and non-negative.

5. Frequently Asked Questions (FAQ)

Q1: Why does the pH change less in buffers than in pure water?
A: Buffers resist pH changes because they contain both weak acid and its conjugate base, which can neutralize added acid or base.

Q2: What is buffer capacity?
A: Buffer capacity is the amount of acid or base that can be added before the pH changes significantly. It's maximum when [HA] = [A⁻].

Q3: When is this equation not valid?
A: The equation may not be accurate when the added acid exceeds the buffer capacity or when concentrations are very dilute.

Q4: How does temperature affect buffer pH?
A: Temperature affects pKa values, so buffer pH may change with temperature. Most pKa values are given at 25°C.

Q5: Can this equation be used for base addition?
A: For base addition, the equation becomes: pH = pKa + log(([A⁻] + added)/([HA] - added))