B dissociates as:
B +H2O -----> BH+ + OH-
0.5 0 0
0.5-x x x
Kb = [BH+][OH-]/[B]
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 ((2.5*10^-6)*0.5) = 1.118*10^-3
since c is much greater than x, our assumption is correct
so, x = 1.118*10^-3 M
So, [OH-] = x = 1.118*10^-3 M
use:
pOH = -log [OH-]
= -log (1.118*10^-3)
= 2.9515
use:
PH = 14 - pOH
= 14 - 2.9515
= 11.0485
Answer: 11.05
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