How is basicity related to pKb?

The pKb value is the numeric measurement of basicity and is related to the shift of the acid-base equilibrium of a compound with water. Therefore, from the pKa value of an acid, one easily knows the pKb value of its conjugated base and viceversa.

What is a pKb value?

pKb is the negative base-10 logarithm of the base dissociation constant (Kb) of a solution. It is used to determine the strength of a base or alkaline solution. Kb = [B+][OH-]/[BOH] pKb = -log Kb. A large Kb value indicates the high level of dissociation of a strong base.

What determines basicity of amines?

The basicity of an amine is increased by electron-donating groups and decreased by electron-withdrawing groups. The basicity of heterocyclic amines depends on the location of the electron pair of the nitrogen atom, its hybridization, and whether or not resonance stabilization is possible.

What does a high pKb mean?

A low pKb means a strong base. Thus, a high pKb means it would be a weaker base. A lower pKb would have a higher pH than a higher pKb value.

How do you calculate basicity order?

The order of basicity is given as I > III > II > IV. So, the correct answer is “Option D”.

Why do alkyl groups increase basicity?

Because alkyl groups donate electrons to the more electronegative nitrogen. The inductive effect makes the electron density on the alkylamine’s nitrogen greater than the nitrogen of ammonium. Correspondingly, primary, secondary, and tertiary alkyl amines are more basic than ammonia.

What is the pKb value of aniline?

The pKb values of ammonia, methenamine and benzenamine (aniline) are 4.75, 3.38 & 9.38 respectively.

What is pKa and pKb value?

pKa and pKb are used to compare the strength of acids and bases respectively. pKa is given for acid dissociations. pKb is given for dissociation of bases. The difference between pKa and pKb is that pKa is the negative logarithm of Ka whereas pKb is the negative logarithm of Kb.