200 Marks in JEE Mains Percentile 2025 - Expected Percentile and Rank

Ka and Kb Relationship - Practice Questions & MCQ

Edited By admin | Updated on Sep 18, 2023 18:35 AM | #JEE Main

Quick Facts

  • 8 Questions around this concept.

Concepts Covered - 1

Relation Between Ka, Kb and Kw for Conjugate Pair

The relation between Ka,Kb and Kw can be understand by the following reaction.
\mathrm{NH_{3}\: +\: H_{2}O\: \rightleftharpoons \: NH_{4}^{+}\: +\: OH^{-}}
Base                      Conjugate acid

The equilibrium constant Kb for base NH3 is given as:
\mathrm{K_{b}\: =\: \frac{[NH_{4}^{+}][OH^{-}]}{NH_{3}}}
Again, the reaction is:
\mathrm{NH_{4}^{+}\: +\: H_{2}O\: \rightleftharpoons \: NH_{3}\: +\: H_{3}O^{+}}

The equilibrium constant Ka for conjugate acid NH4+ is given as:
\mathrm{K_{a}\: =\: \frac{[NH_{3}][H_{3}O^{+}]}{NH_{4}^{+}}}

Thus, \mathrm{K}_{\mathrm{a}} \times \mathrm{K}_{\mathrm{b}}=\left[\mathrm{H}_3 \mathrm{O}^{+}\right]\left[\mathrm{OH}^{-}\right]=\mathrm{K}_{\mathrm{w}}
Thus, \mathrm{K}_{\mathrm{a}} \propto 1 / \mathrm{K}_{\mathrm{b}} at a given temperature

Therefore, if Ka of acid increases, then Kb of the conjugate base decreases. In other words, the conjugate base of strong acid is a weak base and vice-versa.

Study it with Videos

Relation Between Ka, Kb and Kw for Conjugate Pair

"Stay in the loop. Receive exam news, study resources, and expert advice!"

Books

Reference Books

Relation Between Ka, Kb and Kw for Conjugate Pair

Chemistry Part I Textbook for Class XI

Page No. : 222

Line : 22

E-books & Sample Papers

Get Answer to all your questions

Back to top