The pKa Calculator is a chemistry tool that helps you determine the acid dissociation constant (pKa) of acids or bases. By entering the relevant chemical data, the calculator instantly provides the pKa value, which quantifies the strength of an acid in solution.
Understanding pKa is crucial for predicting the ionization of molecules, reaction equilibria, and buffer systems.
The pKa value is related to the acid dissociation constant (Ka), which measures an acid’s tendency to donate a proton (H⁺) in aqueous solution:
Ka = [H⁺][A⁻] / [HA]
pKa = −log₁₀(Ka)
Smaller pKa values indicate stronger acids, while larger values correspond to weaker acids. This concept is central to acid-base chemistry, buffer preparation, and drug design.
The calculator uses the fundamental relationship between Ka and pKa:
pKa = −log₁₀(Ka)
When Ka is unknown but concentrations are given in an equilibrium scenario:
Ka = [H⁺][A⁻] / [HA]
pKa = −log₁₀([H⁺][A⁻] / [HA])
Note: All calculations use molar concentrations in standard units.Problem: Calculate the pKa of acetic acid (CH₃COOH), given Ka = 1.8 × 10⁻⁵.
Step 1: Identify the Ka value
Ka = 1.8 × 10⁻⁵
Step 2: Apply the pKa formula
pKa = −log₁₀(1.8 × 10⁻⁵)
Step 3: Calculate
pKa ≈ 4.74
Final Result:
The pKa of acetic acid is 4.74, indicating it is a weak acid.