Anions as Weak Bases

Like the weak acids, a large number of solutes act as weak bases. It is convenient to classify weak bases into two groups, molecules and anions. 

As pointed out in Section 13.5, anions that are the conjugate bases of weak acids act themselves as weak bases in water They accept a proton from a water molecule, leaving an Oil ion that makes the solution basic. The reactions of the fluoride and carbonate ions are typical ... 

The disproportionation is crucial in determining the action of superoxide anion as a base. According to equation 1, in aqueous solution stoichiometric amounts of the strong bases HO and HO are formed, and the equilibrium constant for this process indicates that superoxide is effective in extracting protons from acids of pK up to 24. In contrast O itself is a weak base (the pK of its conjugate acid, HOj, is 4.69). 

Of these other compounds, alkyl esters of sulfonic acids, ArS020R, are most commonly used in place of alkyl halides usually in the study of reaction mechanisms. but also in synthesis. As the anions of strong acids, sulfonate anions are weak bases and hence are good leaving groups in either nucleophilic substitution or. elimination ... 

Weak-Base Anion Exchange Resin They can be operated only in the acidic pH region where the primary, secondary, or tertiary amine functional groups are protonated, and thus can act as positively charged exchange sites for anions. The weak-base resins remove free mineral acidity, such as HCl or H2SO4, but cannot split salts. Consider the following reaction ... 

Ammonia, amines, and anions of weak acids behave as weak bases in a process associated with a base-dissociation constant, K. The reaction of HA with H2O added to the reaction of A" with H2O gives the reaction for the autoionization of wata thus. Kg x Kb = Ky,. 

Many different types of bases are used in organic chemistry. Common inorganic bases include the anions of weak bases such as water and ammonia (OH and NH2 ). Similar deprotonation of alcohols leads to the alkoxide bases (RO ). Methoxide (MeO ), ethoxide (EtO ), and ferf-butoxide (Me3C-0 ) are very common and are often used in the alcohol solvents from which they were made (methoxide in methanol, tert-butoxide in ferf-butanol, etc.). The bases used to deprotonate water (p fa = 15.8) or alcohols (pATa 18) are sodium hydride (NaH), potassium hydride (KH), sodium and potassium hydroxide (NaOH, KOH), sodium metal (Na°),... 

What is a salt Fist some anions that behave as weak bases in water. Fist some anions that have no basic properties in water. Fist some cations that behave as weak acids in water. Fist some cations that have no acidic properties in water. Using these lists, give some formulas for salts that have only weak base properties in water. What strategy would you use to solve for the pH of these basic salt solutions Identify some salts that have only weak acid properties in water. What strategy would you use to solve for the pH of these acidic salt solutions Identify some salts that have no acidic or basic properties in water (produce neutral solutions). When a salt contains both a weak acid ion and a weak base ion, how do you predict whether the solution pH is acidic, basic, or neutral ... 

Anions of Weak Acids as Weak Bases 599 The Relation Between and f ), of a... 

Methyl and ethyl 2-cyanoacrylates form the basis of so-called super glues . The presence of two electron-withdrawing groups polarizes the carbon-carbon double bond and makes the monomer very susceptible to anionic polymerization. Weak bases such as water bring about rapid polymerization and, in practice, a trace of moisture on a substrate leads to very fast bonding ... 

The anion in each salt is the conjugate base of a weak acid. Therefore, the anions will act as weak bases, making their solutions somewhat basic. The relevant reactions are... 

Conversion of the salt of a weak base into the free base. Prepare a column of a strong base anion resin (such as Amberlite IRA-40o(OH) ) washed with distilled water as above. Drain off most of the water and then allow 100 ml. of A//2.Na.2C03 solution to pass through the column at 5 ml. per minute. Again wash the column with 200 ml. of distilled water. Dissolve 0-05 g. of aniline hydrochloride in 100 ml. of distilled water and pass the solution down the column. The effluent contains aniline in solution and free from all other ions. 

---