The dissociation constant of the base : 7.4 x 10⁻⁴
Further explanation
Butylamine, C4H9NH2 Is A Weak Base
Kb is the dissociation constant of the base.
LOH (aq) ---> L⁺ (aq) + OH⁻ (aq)
[tex]\rm Kb=\dfrac{[L][OH^-]}{[LOH]}[/tex]
[OH⁻] for weak base can be formulated :
[tex]\tt [OH^-]=\sqrt{Kb.M}[/tex]
pH of solution : 12
pH+pOH=14, so pOH :
14-12 = 2, then :
[tex]\tt [OH^-]=10^{-pOH}\\\\(OH^-]=10^{-2}[/tex]
the the dissociation constant (Kb) =
[tex]\tt 10^{-2}=\sqrt{Kb.0.15}\\\\10^{-4}=Kb\times 0.15\\\\Kb=\dfrac{10^{-4}}{0.15}=6.6\times 10^{-4}[/tex]
Or you can use from ICE method :
C4H9NH2(aq) + H2O(l) ⇌ C4H9NH3+(aq) + OH-(aq)
0.15
x x x
0.15-x x x
[tex]\tt Kb=\dfrac{x^2}{0.15-x}\rightarrow x=[OH^-]\\\\Kb=\dfrac{10^{-4}}{0.15-10^{-2}}=7.14\times 10^{-4}[/tex]
