PKb, or the base dissociation constant, is a measure of the strength of a weak base. It is the negative logarithm of the equilibrium constant for the dissociation of the base into its conjugate acid and hydroxide ions.
PKb and pKa are inversely related. The lower the PKb value of a base, the stronger it is, and the higher the pKa value of its conjugate acid, the weaker it is. This is because pKa and PKb are both measures of the strength of an acid or base, but in different contexts.
To calculate PKb, you need to know the initial concentration of the weak base, the concentration of the strong acid added, and the pH at each point during the titration. From this data, you can plot a titration curve and determine the equivalence point, where the base is completely neutralized. Then, using the Henderson-Hasselbalch equation, you can calculate the PKb value.
Like most chemical reactions, the dissociation of a weak base is affected by temperature. As temperature increases, the equilibrium constant for the reaction also increases, leading to a decrease in PKb. This means that weak bases become stronger at higher temperatures.
The stronger the weak base, the lower its PKb value will be. This is because a stronger base will have a higher concentration of hydroxide ions at equilibrium, making it easier for the base to dissociate and resulting in a lower PKb value.