Given that
Ka for HCN is 4.9×10−10 and
Kb for NH3 is 1.8×10−5,
calculate
Kb for CN− and
Ka for NH4+.
Enter the Kb value for CN− followed by the Ka value for NH4+, separated by a comma, using two significant figures.
4 Answers

Divide the numbers given into 1 x 10^14 for your answers.

So, Ka * Kb = Kw
Kw= 1.0 *10^14
and you are given either ka or kb…so its just algebra from there
(Kw) / Ka
( 1.0* 10^14) / ( 4.9 *10^10) = 2.04 *10^5
Kw/Kb
(1.0*10^14) / ( 1.8 * 10^5 ) = 5.55555 * 10 ^ 10

It depends..

Can you elaborate?