Calculate Ph Of Buffer Solution After Adding Hcl

pH Calculation Formula After HCl Addition:

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

New pH:

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1. What is Buffer pH Calculation After HCl Addition?

This calculator determines the new pH of a buffer solution after adding a specified amount of HCl. It uses the Henderson-Hasselbalch equation modified for the addition of strong acid to a weak acid/conjugate base buffer system.

2. How Does the Calculator Work?

The calculator uses the modified Henderson-Hasselbalch equation:

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

Where:

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

Explanation: Adding HCl converts some of the conjugate base (A⁻) to weak acid (HA), changing the ratio in the buffer equation.

3. Importance of Buffer pH Calculation

Details: Accurate pH prediction is crucial for maintaining buffer capacity in chemical and biological systems, pharmaceutical formulations, and laboratory experiments where pH stability is required.

4. Using the Calculator

Tips: Enter pKa value, initial concentrations of conjugate base and weak acid, and the amount of HCl added. Ensure [A⁻] > added to avoid complete consumption of the conjugate base.

5. Frequently Asked Questions (FAQ)

Q1: What happens if added HCl exceeds [A⁻]?
A: The calculation becomes invalid as it would result in negative concentration values. The buffer capacity is exceeded.

Q2: Can this calculator be used for other strong acids?
A: Yes, the calculation is the same for any monoprotic strong acid added to the buffer system.

Q3: Does volume change affect the calculation?
A: This calculation assumes concentrations are used (not affected by volume changes). For significant volume changes, concentration corrections may be needed.

Q4: What are typical pKa values for common buffers?
A: Acetic acid: 4.76, Phosphoric acid (pKa2): 7.20, TRIS: 8.08. Different buffers have different pKa values.

Q5: How accurate is this calculation?
A: The calculation provides a good approximation for dilute solutions where activity coefficients are close to 1. For precise work, activity corrections may be needed.