Acid Dissociation (pKa) Calculator

Calculate pKa, Ka, pH, and acid-base ratios with ease.

Enter the known values and select what you want to calculate. This tool supports Ka ↔ pKa conversion and Henderson-Hasselbalch equation for buffer solutions.

Examples

See how to use the pKa Calculator in real scenarios.

Calculate pKa from Ka

Calculate pKa from Ka

Find the pKa of acetic acid given Ka = 1.8e-5.

Calculation Type: type_pka

Ka Value: 1.8e-5

pKa Value: undefined

pH Value: undefined

[A-]/[HA] Ratio: undefined

[A-] (mol/L): undefined mol/L

[HA] (mol/L): undefined mol/L

Calculate Ka from pKa

Calculate Ka from pKa

Find the Ka value when pKa = 4.75.

Calculation Type: type_ka

Ka Value: undefined

pKa Value: 4.75

pH Value: undefined

[A-]/[HA] Ratio: undefined

[A-] (mol/L): undefined mol/L

[HA] (mol/L): undefined mol/L

Calculate pH from pKa and ratio

Calculate pH from pKa and ratio

Find the pH of a buffer where pKa = 4.75 and [A-]/[HA] = 1.

Calculation Type: type_ph

Ka Value: undefined

pKa Value: 4.75

pH Value: undefined

[A-]/[HA] Ratio: 1

[A-] (mol/L): undefined mol/L

[HA] (mol/L): undefined mol/L

Calculate [A-]/[HA] ratio from pH and pKa

Calculate [A-]/[HA] ratio from pH and pKa

Find the [A-]/[HA] ratio for a buffer with pH = 5.75 and pKa = 4.75.

Calculation Type: type_ratio

Ka Value: undefined

pKa Value: 4.75

pH Value: 5.75

[A-]/[HA] Ratio: undefined

[A-] (mol/L): undefined mol/L

[HA] (mol/L): undefined mol/L

Other Titles
Understanding Acid Dissociation (pKa) Calculator: A Comprehensive Guide
Master acid-base chemistry with pKa, Ka, and buffer calculations.

What is pKa and Why is it Important?

  • Definition of pKa
  • Relationship between Ka and pKa
  • Significance in Chemistry
pKa is the negative base-10 logarithm of the acid dissociation constant (Ka). It is a key parameter in acid-base chemistry, indicating the strength of an acid in solution.
pKa = -log10(Ka)
A lower pKa value means a stronger acid. Understanding pKa helps in predicting reaction direction, buffer capacity, and biological activity.

pKa in Real Acids

  • Acetic acid has a Ka of 1.8e-5, so pKa = 4.74.
  • A strong acid like HCl has a very low pKa.

Step-by-Step Guide to Using the pKa Calculator

  • Choosing the Calculation Type
  • Entering the Correct Values
  • Interpreting the Results
Select what you want to calculate: pKa, Ka, pH, or [A-]/[HA] ratio. Enter the required values as prompted by the calculator.
User-Friendly Interface
The calculator will validate your inputs and display the result instantly, along with units and explanations.

How to Use the Calculator

  • To find pKa, enter Ka and select 'pKa (from Ka)'.
  • To find pH, enter pKa and the ratio, then select 'pH (from pKa and ratio)'.

Real-World Applications of pKa Calculations

  • Buffer Solution Design
  • Pharmaceutical Chemistry
  • Biological Systems
pKa calculations are essential in designing buffer solutions, drug formulation, and understanding enzyme activity in biological systems.
Buffer Capacity and pKa
Choosing the right pKa is crucial for effective buffering at a desired pH.

Applications in Science

  • Preparing a buffer at pH 7.4 for biological experiments.
  • Selecting a drug with optimal pKa for absorption.

Common Misconceptions and Correct Methods

  • Confusing pKa and Ka
  • Incorrect Use of Logarithms
  • Ignoring Units
Many confuse pKa with Ka or use incorrect logarithm bases. Always use base-10 logarithms and check units.
Best Practices
Ensure all concentrations are in mol/L and logarithms are base-10 for accurate results.

Avoiding Mistakes

  • Do not use natural log (ln) for pKa calculations.
  • Always input Ka as a positive number.

Mathematical Derivation and Examples

  • Deriving pKa from Ka
  • Using Henderson-Hasselbalch Equation
  • Worked Examples
pKa is derived from Ka using the formula: pKa = -log10(Ka). The Henderson-Hasselbalch equation relates pH, pKa, and the ratio of [A-] to [HA].
Henderson-Hasselbalch: pH = pKa + log10([A-]/[HA])
Practice with real values to master the calculations.

Mathematical Examples

  • Given Ka = 1.8e-5, pKa = 4.74.
  • Given pKa = 4.75 and [A-]/[HA] = 1, pH = 4.75.