Calculadora de pKa
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
pKa = −log₁₀(Ka) ; pKb = 14 − pKa
About this calculator
The pKa calculator converts between pKa and Ka using the relation pKa = −log₁₀(Ka). Simply enter one value to instantly obtain the other. The tool also calculates pKb from the equation pKb = 14 − pKa, useful for conjugate acids and bases.
pKa is a measure of acid strength: the lower the pKa, the stronger the acid. For weak acids, pKa is greater than zero. This calculator is helpful for chemists, students, and professionals who need to relate acid dissociation constants in titrations, buffer preparation, or chemical equilibrium studies.
Use this calculator whenever you need to convert Ka (acid dissociation constant) to pKa or vice versa. It is common in analytical, pharmaceutical, and biochemistry labs. It also helps calculate pKb of conjugate bases, essential for understanding acid-base reactions.
Cautions: ensure the Ka value is in correct scientific notation (e.g., 1.8e-5). The calculator assumes standard temperature (25°C), as pKa may vary with temperature. Do not use for very strong acids or bases (Ka > 1), as the logarithmic approximation may not be accurate.
Frequently asked questions
What does pKa mean?
pKa is the negative logarithm of the acid dissociation constant Ka. It indicates acid strength: the lower the pKa, the stronger the acid.
How do I convert Ka to pKa?
Use the formula pKa = −log₁₀(Ka). For example, if Ka = 1.8e-5, then pKa = −log₁₀(1.8e-5) ≈ 4.74.
What is pKb and how does it relate to pKa?
pKb is the negative logarithm of the base dissociation constant. For a conjugate acid-base pair, pKa + pKb = 14 at 25°C.
Does this calculator work for strong acids?
For strong acids (Ka > 1), pKa is negative. The calculator can handle these values, but note that pKa is less commonly used for strong acids.
Does temperature affect pKa?
Yes, pKa varies with temperature. This calculator assumes 25°C. For other temperatures, consult tabulated values or adjust the dissociation constant.