1. What is the Henderson-Hasselbalch Equation?

The Henderson-Hasselbalch equation is used to estimate the pH of a buffer solution. It relates the pH, pKa (acid dissociation constant), and the ratio of the concentrations of the conjugate base and weak acid in the buffer system.

2. How Does the Calculator Work?

The calculator uses the Henderson-Hasselbalch equation:

Where:

• \( pH \) — pH value of the solution (dimensionless)
• \( pKa \) — Acid dissociation constant (dimensionless)
• \( [base] \) — Concentration of base (mol/L)
• \( [acid] \) — Concentration of acid (mol/L)

For 0.1 M NH₄OH/NH₄⁺ buffer: pKa of NH₄⁺ = 9.25, and when concentrations are equal (0.1 M each), pH = pKa = 9.25

3. Importance of pH Calculation in Buffer Solutions

Details: Buffer solutions resist changes in pH when small amounts of acid or base are added. Accurate pH calculation is crucial for various chemical and biological processes, including maintaining optimal conditions for enzymatic reactions and pharmaceutical formulations.

4. Using the Calculator

Tips: Enter pKa value, base concentration, and acid concentration in mol/L. All values must be positive numbers. For the NH₄OH/NH₄⁺ buffer system, use pKa = 9.25.

5. Frequently Asked Questions (FAQ)

Q1: What is the pKa value for NH₄⁺?
A: The pKa value for ammonium ion (NH₄⁺) is 9.25 at 25°C.

Q2: Why does pH equal pKa when concentrations are equal?
A: When [base] = [acid], the log term becomes log(1) = 0, so pH = pKa + 0 = pKa.

Q3: What are typical buffer concentration ranges?
A: Buffer concentrations typically range from 0.01 M to 0.1 M for most laboratory applications.

Q4: Does temperature affect pKa values?
A: Yes, pKa values are temperature-dependent. The value 9.25 is typically given for 25°C.

Q5: Can this calculator be used for other buffer systems?
A: Yes, the Henderson-Hasselbalch equation is general and can be applied to any acid-base buffer system by using the appropriate pKa value.