Constants | Periodic Table The degree to which a weak base dissociates is given
ID: 1034315 • Letter: C
Question
Constants | Periodic Table The degree to which a weak base dissociates is given by the base-ionization constant, Kb. For the generic weak base, B(a) +H2O) BH (aq) OH (aq) this constant is given by Strong bases will have a higher Kb value. Similarly, strong bases will have a higher percent ionization value. Percent ionization O [B]initial-x100% B initial Strong bases, for which K, is very large, ionize completely (100 %). For weak bases, the percent ionization changes with concentration. The more dilute the solution, the greater the percent ionization.Explanation / Answer
NH3 + H2O ----------> NH4^+ + OH^-
I 0.215 0 0
C -x +x +x
E 0.215-x +x +x
Kb = [NH4^+][OH^-]/[NH3]
1.8*10^-5 = x*x/0.215-x
1.8*10^-5*(0.215-x) = x^2
x = 0.00196
[OH^-] = x = 0.00196M
POH = -log[OH^-]
= -log0.00196
= 2.7077
PH = 14-POH
= 14-2.7077 = 11.2923
percent ionisation = [OH^-] equilibrium *100/initial conc
= 0.00196*100/0.215 = 0.912%