Careers360 Logo
ask-icon
share
    JEE Main 2026 City Intimation Slip for B.Tech Session 2 (Out); NTA JEE Exam City Allotment

    Ka and Kb Relationship - Practice Questions & MCQ

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

    Quick Facts

    • 11 Questions around this concept.

    Solve by difficulty

    The pH of 1N aqueous solutions of HCl, CH3COOH and HCOOH follows the order

    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!"

    Get Answer to all your questions