C5H5N dissociates as:
C5H5N +H2O -----> C5H5NH+ + OH-
2.5*10^-2 0 0
2.5*10^-2-x x x
Kb = [C5H5NH+][OH-]/[C5H5N]
Kb = x*x/(c-x)
Assuming x can be ignored as compared to c
So, above expression becomes
Kb = x*x/(c)
so, x = sqrt (Kb*c)
x = sqrt ((1.7*10^-9)*2.5*10^-2) = 6.519*10^-6
since c is much greater than x, our assumption is correct
so, x = 6.519*10^-6 M
So, [OH-] = x = 6.519*10^-6 M
use:
pOH = -log [OH-]
= -log (6.519*10^-6)
= 5.1858
use:
PH = 14 - pOH
= 14 - 5.1858
= 8.8142
Answer: 8.81
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