Calculate Ph Of Buffer After Adding Hcl

Buffer pH Equation After Adding HCl:

\[ \text{pH}_{\text{new}} = \text{pKa} + \log\left( \frac{[\text{A}^-] - \text{added}}{[\text{HA}] + \text{added}} \right) \]

pKa:

dimensionless

[A⁻]:

mol/L

[HA]:

mol/L

Added HCl:

mol

pH_new:

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1. What is the Buffer pH Equation After Adding HCl?

The buffer pH equation calculates the new pH of a buffer solution after adding a strong acid (HCl). It's based on the Henderson-Hasselbalch equation and accounts for the consumption of conjugate base and formation of weak acid.

2. How Does the Calculator Work?

The calculator uses the buffer pH equation:

\[ \text{pH}_{\text{new}} = \text{pKa} + \log\left( \frac{[\text{A}^-] - \text{added}}{[\text{HA}] + \text{added}} \right) \]

Where:

\( \text{pKa} \) — Acid dissociation constant (dimensionless)
\( [\text{A}^-] \) — Concentration of conjugate base (mol/L)
\( [\text{HA}] \) — Concentration of weak acid (mol/L)
\( \text{added} \) — Amount of HCl added (mol)

Explanation: The equation shows how adding strong acid decreases the conjugate base concentration and increases the weak acid concentration, thus changing the pH.

3. Importance of Buffer pH Calculation

Details: Calculating pH changes in buffer solutions is crucial for understanding buffer capacity, predicting chemical behavior, and designing experiments in biochemistry and analytical chemistry.

4. Using the Calculator

Tips: Enter pKa value, initial concentrations of conjugate base and weak acid, and amount of HCl added. All concentrations must be positive values, and added HCl should not exceed the available 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 of conjugate base, indicating the buffer capacity has been exceeded.

Q2: Why use this specific equation?
A: This equation specifically accounts for the stoichiometric changes when strong acid is added to a weak acid/conjugate base buffer system.

Q3: Does this work for other strong acids?
A: Yes, the equation works for any strong acid addition, as all strong acids completely dissociate and react equivalently with the conjugate base.

Q4: What are the limitations of this calculation?
A: The calculation assumes ideal behavior, constant temperature, and that the added volume is negligible compared to the total buffer volume.

Q5: How accurate is this calculation?
A: The calculation provides a good estimate for dilute solutions where activity coefficients are close to 1, but may need adjustment for concentrated solutions.