Ka and Kb Relationship Calculator
Relate Ka and Kb for a conjugate pair.
Formula first
Overview
This equation defines the inverse mathematical relationship between the dissociation constants of a conjugate acid-base pair in aqueous solution. It states that the product of the acid dissociation constant (Ka) and its conjugate base dissociation constant (Kb) is equal to the autoionization constant of water (Kw).
Symbols
Variables
K_a = Acid Const Ka, K_b = Base Const Kb, K_w = Kw Constant
Apply it well
When To Use
When to use: This formula is used when you need to find the strength of a conjugate base given the strength of its parent acid, or vice versa. It is only applicable to conjugate pairs in aqueous systems, typically at a standard temperature of 25°C where Kw is a known constant.
Why it matters: Understanding this relationship is essential for predicting the pH of salt solutions and the buffering capacity of chemical systems. It quantifies the principle that the conjugate of a strong acid is a weak base, which is a foundational concept in analytical chemistry and biochemistry.
Avoid these traps
Common Mistakes
- Using non-conjugate pairs.
- Forgetting Kw changes with temperature.
One free problem
Practice Problem
A specific weak acid has a dissociation constant (Ka) of 1.8 × 10⁻⁵ at 25°C. Calculate the base dissociation constant (Kb) for its conjugate base.
Solve for:
Hint: Divide the water autoionization constant (Kw) by the given Ka value.
The full worked solution stays in the interactive walkthrough.
References
Sources
- Atkins' Physical Chemistry
- IUPAC Gold Book: acid dissociation constant
- IUPAC Gold Book: base dissociation constant
- IUPAC Gold Book: autoionization of water
- Wikipedia: Conjugate acid-base pair
- IUPAC Gold Book: 'acid dissociation constant, Ka'
- IUPAC Gold Book: 'base dissociation constant, Kb'
- IUPAC Gold Book: 'ionic product of water, Kw'