Models of Acids and Bases Arrhenius Concept: Acids produce H+ in solution, bases produce OH ion. Brønsted-Lowry: Acids are H+ donors, bases are proton acceptors. HCl + H2O Cl + H3O+ acid base Copyright©2000 by Houghton Mifflin Company. All rights reserved.
Conjugate Acid/Base Pairs HA(aq) + H2O(l) H3O+(aq) + A(aq) conj conj conj conj acid 1 base 2 acid 2 base 1 conjugate base: everything that remains of the acid molecule after a proton is lost. conjugate acid: formed when the proton is transferred to the base. Copyright©2000 by Houghton Mifflin Company. All rights reserved.
Acid Dissociation Constant (Ka) HA(aq) + H2O(l) H3O+(aq) + A(aq) Copyright©2000 by Houghton Mifflin Company. All rights reserved.
Copyright©2000 by Houghton Mifflin Company. All rights reserved. Acid Strength Strong Acid: Its equilibrium position lies far to the right. (HNO3) Yields a weak conjugate base. (NO3) Copyright©2000 by Houghton Mifflin Company. All rights reserved.
Acid Strength (continued) Weak Acid: Its equilibrium lies far to the left. (CH3COOH) Yields a much stronger (it is relatively strong) conjugate base than water. (CH3COO) Copyright©2000 by Houghton Mifflin Company. All rights reserved.
Water as an Acid and a Base Water is amphoteric (it can behave either as an acid or a base). H2O + H2O H3O+ + OH conj conj acid 1 base 2 acid 2 base 1 Kw = 1 1014 at 25°C Copyright©2000 by Houghton Mifflin Company. All rights reserved.
Copyright©2000 by Houghton Mifflin Company. All rights reserved. The pH Scale pH log[H+] pH in water ranges from 0 to 14. Kw = 1.00 1014 = [H+] [OH] pKw = 14.00 = pH + pOH As pH rises, pOH falls (sum = 14.00). Copyright©2000 by Houghton Mifflin Company. All rights reserved.
Solving Weak Acid Equilibrium Problems List major species in solution. Choose species that can produce H+ and write reactions. Based on K values, decide on dominant equilibrium. Write equilibrium expression for dominant equilibrium. List initial concentrations in dominant equilibrium. Copyright©2000 by Houghton Mifflin Company. All rights reserved.
Solving Weak Acid Equilibrium Problems (continued) Define change at equilibrium (as “x”). Write equilibrium concentrations in terms of x. Substitute equilibrium concentrations into equilibrium expression. Solve for x the “easy way.” Verify assumptions using 5% rule. Calculate [H+] and pH. Copyright©2000 by Houghton Mifflin Company. All rights reserved.
Percent Dissociation (Ionization) Copyright©2000 by Houghton Mifflin Company. All rights reserved.
Bases “Strong” and “weak” are used in the same sense for bases as for acids. strong = complete dissociation (hydroxide ion supplied to solution) NaOH(s) Na+(aq) + OH(aq) Copyright©2000 by Houghton Mifflin Company. All rights reserved.
Bases (continued) weak = very little dissociation (or reaction with water) H3CNH2(aq) + H2O(l) H3CNH3+(aq) + OH(aq) Copyright©2000 by Houghton Mifflin Company. All rights reserved.
Copyright©2000 by Houghton Mifflin Company. All rights reserved. Polyprotic Acids . . . can furnish more than one proton (H+) to the solution. Copyright©2000 by Houghton Mifflin Company. All rights reserved.
Acid-Base Properties of Salts Copyright©2000 by Houghton Mifflin Company. All rights reserved.
Structure and Acid-Base Properties Two factors for acidity in binary compounds: Bond Polarity (high is good) Bond Strength (low is good) Copyright©2000 by Houghton Mifflin Company. All rights reserved.
Copyright©2000 by Houghton Mifflin Company. All rights reserved. Oxides Acidic Oxides (Acid Anhydrides): OX bond is strong and covalent. SO2, NO2, CrO3 Basic Oxides (Basic Anhydrides): OX bond is ionic. K2O, CaO Copyright©2000 by Houghton Mifflin Company. All rights reserved.
Copyright©2000 by Houghton Mifflin Company. All rights reserved. Lewis Acids and Bases Lewis Acid: electron pair acceptor Lewis Base: electron pair donor Copyright©2000 by Houghton Mifflin Company. All rights reserved.