Acid dissociation constant Calculator
Expression for Ka of a weak acid.
Formula first
Overview
The acid dissociation constant, Ka, is an equilibrium constant that measures the quantitative strength of an acid in an aqueous solution. It describes the ratio of the concentrations of the dissociated ions to the undissociated acid molecules at equilibrium.
Symbols
Variables
[H^+] = Hydrogen Ion, [A^-] = Conjugate Base, acid = Acid, K_a = Acid Dissociation Constant
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When To Use
When to use: This equation is used when calculating the extent of ionization for weak acids in water, as strong acids are assumed to dissociate completely. It is applicable in scenarios involving pH determination, buffer capacity calculations, and titration analysis in dilute solutions.
Why it matters: Ka values allow chemists to predict the acidity of a solution and the protonation state of molecules, which is vital in drug design and biochemistry. Understanding these constants is essential for controlling chemical reactions in industrial processes where pH must remain within a specific range.
Avoid these traps
Common Mistakes
- Using initial instead of equilibrium concentrations.
- Forgetting the denominator.
One free problem
Practice Problem
A 0.10 M solution of a generic weak acid HA reaches equilibrium. The concentration of both H⁺ and A⁻ ions is measured to be 0.00134 M, and the remaining undissociated HA is 0.09866 M. Calculate the acid dissociation constant Ka.
Solve for: Ka
Hint: Square the ion concentration and divide by the concentration of the neutral acid.
The full worked solution stays in the interactive walkthrough.
References
Sources
- IUPAC Gold Book: Acid dissociation constant
- Atkins' Physical Chemistry
- Wikipedia: Acid dissociation constant
- IUPAC Gold Book: 'acid dissociation constant'
- General Chemistry: Principles and Modern Applications by Petrucci, Herring, Madura, Bissonnette
- Atkins' Physical Chemistry, 11th Edition
- Edexcel A-Level Chemistry — Acid-Base Equilibria