Caution : anions with ionizable hydrogen atoms can undergo acid hydrolysis. To determine which reaction dominates, we need to compare the equilibrium constants: the larger equilibrium constant wins. Chemistry Hydrolysis : the reaction of a substance with water. Both cations and anions can undergo hydrolysis, but not all ions react in this fashion.
Typically, this is a three step process. Write the reaction that dissociates the salt into its constituent ions. Hydrolysis, on the other hand, involves an actual chemical reaction of the water molecule itself with another reactant. Aluminum ion, for example, can bond with six water molecules to form the hydrated aluminum ion. In water, however, the hydrated ion can undergo hydrolysis; some of the hydrated molecules contribute a hydrogen ion to the solution , making the solution acidic.
Solutions of non-hydrated ions often become either acidic or basic because of hydrolysis, too. The conjugate base produced by this process contains five other bonded water molecules capable of acting as acids, and so the sequential or step-wise transfer of protons is possible as depicted in few equations below:. This is an example of a polyprotic acid, the topic of discussion in a later section of this chapter. Aside from the alkali metals group 1 and some alkaline earth metals group 2 , most other metal ions will undergo acid ionization to some extent when dissolved in water.
The acid strength of these complex ions typically increases with increasing charge and decreasing size of the metal ions. The first-step acid ionization equations for a few other acidic metal ions are shown below:. Solution The equation for the reaction and K a are:. An ICE table with the provided information is. Substituting the expressions for the equilibrium concentrations into the equation for the ionization constant yields:.
The ICE table defined x as equal to the hydronium ion concentration, and so the pH is calculated to be. Check Your Learning What is in a 0. The ions composing salts may possess acidic or basic character, ionizing when dissolved in water to yield acidic or basic solutions. Acidic cations are typically the conjugate partners of weak bases, and basic anions are the conjugate partners of weak acids. Many metal ions bond to water molecules when dissolved to yield complex ions that may function as acids.
Determine whether aqueous solutions of the following salts are acidic, basic, or neutral:. Is a solution of novocaine acidic or basic? Skip to content Acid-Base Equilibria. Learning Objectives By the end of this section, you will be able to: Predict whether a salt solution will be acidic, basic, or neutral Calculate the concentrations of the various species in a salt solution Describe the acid ionization of hydrated metal ions.
Salts with Acidic Ions Salts are ionic compounds composed of cations and anions, either of which may be capable of undergoing an acid or base ionization reaction with water.
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