a weak acid has dissociation constant 10-5what is its equilibrium cinstant with strong base?

There exists a relationship between the value of K_a for an acid HA and the value of K_b for its conjugate base A^–. Since adding the ionization reaction for HA and the ionization reaction of A^– always gives the reaction for the self-ionization of water, the product of the acidity and basicity constants gives the dissociation constant of water (K_w), which is 1.0 × 10^-14 M² at 25°C. In other words,

K_a*K_b = K_w

kb = 10^-14 / 10^-5

    = 10^-9

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regards

ramesh