1)
Given:
pKb = 8.75
use:
pKb = -log Kb
8.75= -log Kb
Kb = 1.778*10^-9
C5H5N dissociates as:
C5H5N +H2OÂ Â Â Â
----->Â Â Â Â C5H5NH+Â Â +Â Â
OH-
0.32Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â
0Â Â Â Â Â Â Â Â 0
0.32-x               Â
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 ((1.778*10^-9)*0.32) = 2.385*10^-5
since c is much greater than x, our assumption is correct
so, x = 2.385*10^-5 M
So, [OH-] = x = 2.385*10^-5 M
use:
pOH = -log [OH-]
= -log (2.385*10^-5)
= 4.6224
use:
PH = 14 - pOH
= 14 - 4.6224
= 9.3776
Answer: 9.38
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