Henderson-Hasselbalch Equation Calculator

Buffer pH, pKa, and Concentration Calculator

Calculate the pH of buffer solutions, pKa, or unknown concentrations using the Henderson-Hasselbalch equation. Enter any three values to solve for the fourth.

Practical Examples

See how the Henderson-Hasselbalch equation is used in real scenarios.

Calculate pH of Acetic Acid Buffer

pH Calculation

Given pKa = 4.75, [HA] = 0.1 M, [A-] = 0.2 M, find the pH.

pKa: 4.75

Ka:

[HA] (Acid): 0.1

[A-] (Base): 0.2

pH:

Unit: mol/L (M)

Find Acid Concentration for Target pH

Acid Concentration

Given pKa = 7.2, [A-] = 0.05 M, pH = 7.4, find [HA] needed.

pKa: 7.2

Ka:

[HA] (Acid):

[A-] (Base): 0.05

pH: 7.4

Unit: mol/L (M)

Find Base Concentration for Target pH

Base Concentration

Given pKa = 6.3, [HA] = 0.03 M, pH = 6.8, find [A-] needed.

pKa: 6.3

Ka:

[HA] (Acid): 0.03

[A-] (Base):

pH: 6.8

Unit: mol/L (M)

Calculate pKa from pH and Concentrations

pKa Calculation

Given pH = 5.0, [HA] = 0.2 M, [A-] = 0.1 M, find pKa.

pKa:

Ka:

[HA] (Acid): 0.2

[A-] (Base): 0.1

pH: 5

Unit: mol/L (M)

Other Titles
Understanding the Henderson-Hasselbalch Equation Calculator: A Comprehensive Guide
Master buffer pH calculations, pKa, and more with this powerful chemistry tool.

What is the Henderson-Hasselbalch Equation?

  • Definition and Origin
  • Mathematical Formulation
  • Importance in Chemistry
The Henderson-Hasselbalch equation is a fundamental formula in chemistry that relates the pH of a buffer solution to the concentration of its acid and conjugate base components. It is widely used to estimate the pH of buffer solutions in laboratories, classrooms, and industry.
Henderson-Hasselbalch Equation
pH = pKa + log10([A-]/[HA])

Common Use Cases

  • Calculating the pH of an acetic acid/acetate buffer.
  • Determining the required acid concentration for a target pH.
  • Finding pKa from experimental pH and concentrations.

Step-by-Step Guide to Using the Calculator

  • Input Field Descriptions
  • How to Solve for Any Variable
  • Tips for Accurate Results
To use the calculator, enter any three of the following: pKa (or Ka), [HA], [A-], or pH. Leave the field you want to solve for empty. The calculator will automatically determine which variable to compute.
Input Tips
Ensure all concentrations use the same unit. If Ka is entered, pKa will be calculated automatically.

Step-by-Step Examples

  • Enter pKa, [HA], and [A-] to find pH.
  • Enter pH, [A-], and [HA] to find pKa.
  • Enter pKa, pH, and [A-] to find [HA].

Real-World Applications of the Henderson-Hasselbalch Equation

  • Biochemistry and Medicine
  • Pharmaceutical Industry
  • Environmental Science
The equation is essential for preparing buffer solutions in biochemistry, controlling pH in pharmaceutical formulations, and monitoring environmental water quality.
Practical Applications
It is used in titration curves, enzyme kinetics, and blood pH regulation studies.

Application Scenarios

  • Buffer preparation for enzyme assays.
  • Designing pharmaceutical buffers.
  • Assessing acid rain impact on lakes.

Common Misconceptions and Correct Methods

  • Misuse of the Equation
  • Unit Consistency
  • Logarithm Calculations
A common mistake is using different units for [HA] and [A-]. Always use the same unit for both. Also, ensure you never take the logarithm of zero or a negative number.
Best Practices
Double-check your inputs and use the calculator's validation messages for guidance.

Mistakes to Avoid

  • Entering [HA] in mmol/L and [A-] in mol/L (incorrect).
  • Leaving more than one field empty (incorrect).
  • Entering a negative concentration (incorrect).

Mathematical Derivation and Worked Examples

  • Derivation from Acid Dissociation
  • Sample Calculations
  • Interpreting Results
The equation is derived from the definition of pH and the acid dissociation constant (Ka). It provides a practical way to relate measurable quantities in buffer solutions.
Worked Example
Given pKa = 4.75, [HA] = 0.1 M, [A-] = 0.2 M: pH = 4.75 + log10(0.2/0.1) = 5.05.

Worked Examples

  • Calculate pH for a phosphate buffer.
  • Find pKa from titration data.
  • Determine [A-] for a desired pH.