Bases ionization constants

Kb is also widely called the base ionization constant. 

In the presence of a base B, water acts as an acid by donating a proton, and the equiiibrium constant for the transfer of a proton from water to a base is caiied the base ionization constant (Zjj) ... 

Kjj is the base dissociation constant, or base ionization constant, that measures a base s strength. Some values are given for bases in Table 3. 

In performing a calculation based on an acid or base ionization constant expression such as Eqs. (13-7) or (13-8), there are often many unknowns. Remember that in an algebraic problem involving multiple unknowns, one needs as many equations as there are unknowns. The equilibrium constant expression itself is one equation, and the Kw expression is always available. Two other types of equation are often useful equations expressing... 

At this point, the calculation becomes a little different. Because the benzoate ion is a base, the equilibrium constant expression must be the base ionization constant, Kb. You haven t been given the value of Kb, however, so you will have to generate it using Equation 13.8 ... 

The higher the ionization constant, the stronger the acid, and consequently the weaker the base. Thus the value of Ka is at the same time a measure of the strength of the base there is no need to define a base ionization constant separately. 

Because [H2O] is a constant, the constants are collected on the left-hand side of the equation to derive the base ionization constant expression ... 

A strong base is a substance that reacts completely with water, so that the base ionization constant defined in Eq. (14) or (15) is effectively infinite. This situation can only be realized if the conjugate acid of the strong base is very weak. A weak base will be characterized by a base ionization constant that is considerably less than unity, so that the position of equilibrium in the reaction represented in Eq. (12) favors the existence of unreacted free base. 

Because aqueous solutions of anions are commonly prepared by the dissolution of a salt containing that anion, reactions of the type described by Eq. (16) are often termed hydrolysis reactions. Eq. (16) is necessarily characterized by its base ionization constant expression ... 

For more practice writing base ionization constant expressions, go to Supplemental Practice Problems in Appendix A. 

Base ionization constants You won t be surprised to leam that like weak acids, weak bases also form equihbrium mixtures of molecules and ions in aqueous soluhon. Therefore, the equilibrium constant provides a measure of the extent of the base s ionization. The equilibrium constant for the ionization of methylamine in water is defined by this equilibrium constant expression. 

The constant is called the base ionizahon constant. The base ionization constant is the value of the equilibrium constant expression for the ionizahon of a base. The smaller the value of K, the weaker the base. values and ionization equahons for several weak bases are listed in Table 19-4. 

Write ionization equations and base ionization constant expressions for the following bases. 

For weak acids and weak bases, the value of the acid or base ionization constant is a measure of the strength of the acid or base. 

Write the equation for the ionization reaction and the base ionization constant expression for ethylamine (C2H5NH2) in water. 

Write the base ionization constant expression for ammonia. 

For weak acids, the magnitude of is very small, and as a result the resulting H3O+ and A ions will be produced in small amounts. Under those conditions, both Yjj+ and y will be approximately equal to one, and then one can approximate the thermodynamic equilibrium constant, K, by the concentration-based ionization constant, Ka. 

The basic substance (B) that originally accepted the proton becomes the conjugate acid (BH+) of that substance, since the conjugate acid could conceivably donate a proton to an even stronger base than the original substance. The concentration-based ionization constant expression corresponding to equation... 

---