Dissociation constants for bases

Weak bases only partially accept protons from the solvent and are characterized by a base dissociation constant, kj,. For example, the base dissociation reaction and base dissociation constant for the acetate ion are... 

Table 8.3 lists the base dissociation constants for several weak bases at 25°C. Nitrogen-containing compounds are Bronsted-Lowry bases, because the lone pair of electrons on a nitrogen atom can bond with H+ from water. The steps for solving problems that involve weak bases are similar to the steps you learned for solving problems that involve weak acids. 

Pyridine, C5H5N, is used to manufacture medications and vitamins. Calculate the base dissociation constant for pyridine if a 0.125 mol/L aqueous solution has a pH of 9.10. 

For any conjugate acid-base pair, the product of the acid-dissociation constant for the acid and the base-dissociation constant for the base always equals the ion-product constant for water ... 

The equilibrium constant (Kb) for this reaction is called the base-dissociation constant for the base A-. Because this constant spans a wide range of values, it is often given in logarithmic form. The negative logarithm (base 10) of Kb is defined as pA b-... 

Because amines are fairly strong bases, their aqueous solutions are basic. An amine can abstract a proton from water, giving an ammonium ion and a hydroxide ion. The equilibrium constant for this reaction is called the base-dissociation constant for the amine, symbolized by Kb. 

The acid dissociation constant for HBrO is 2 x 10 9. What is the base dissociation constant for BrO" ... 

Although the acid-dissociation constant for phenol (CgHjOH) is listed in Appendix D, the base-dissociation constant for the phenolate ion (CgHsO ) is not. (a) Explain why it is not necessary to list both for phenol and Ky for the phenolate ion. (b) Calculate Ky for the phenolate ion. (c) Is the phenolate ion a weaker or stronger base than ammonia ... 

Plan The major species in the solution will be iSIH4 Cr,and NH3. Of these, the Q ion is a spectator (it is the conjugate base of a strong add). Thus, the NH4" -NH3 conjugate acid-base pair will determine the pH of the buffer solution. The equilibrium relationship between NH4 and NH3 is given by the base-dissociation constant for NH3 ... 

We can turn the above arguments around and compare the strengths of weak bases, A , such as acetate, by the extent to which they can retrieve a proton from water. A base, A , removes a proton from water to form hydroxide ion and the conjugate acid, HA. The base dissociation constant, for the reaction is analogous to the acid dissociation constant, AT. 

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