Common household substances that contain acids and bases. Vinegar is a dilute solution of acetic acid. Drain cleaners contain strong bases such as sodium hydroxide. 14a–1 Copyright © Houghton Mifflin Company. All rights reserved.

14b–2 Copyright © Houghton Mifflin Company. All rights reserved.

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 + H 2 O  Cl  + H 3 O + acid base Copyright©2000 by Houghton Mifflin Company. All rights reserved.3

Conjugate Acid/Base Pairs  HA(aq) + H 2 O(l)  H 3 O + (aq) + A  (aq) conj conj acid base acid base  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.4

Figure 14.1: The reaction of HCl and H 2 O. 14a–5 Copyright © Houghton Mifflin Company. All rights reserved. Base Acid conj. acid conj. base

14.2 Acid Strength 4 Its equilibrium position lies far to the right. (HNO 3 )  Yields a weak conjugate base. (NO 3  ) Copyright©2000 by Houghton Mifflin Company. All rights reserved.6 Strong Acid:

Acid Strength (continued) 4 Its equilibrium lies far to the left. (CH 3 COOH)  Yields a much stronger (it is relatively strong) conjugate base than water. (CH 3 COO  ) Copyright©2000 by Houghton Mifflin Company. All rights reserved.7 Weak Acid:

Figure 14.6: (a) A strong acid HA is completely ionized in water. (b) A weak acid HB exists mostly as undissociated HB molecules in water. Note that the water molecules are not shown in this figure. 14a–8 Copyright © Houghton Mifflin Company. All rights reserved.

Figure 14.4: Graphic representation of the behavior of acids of different strengths in aqueous solution. (a) A strong acid. (b) A weak acid.

Figure 14.5: The relationshi p of acid strength and conjugate base strength for the reaction

Polyprotic Acids ... can furnish more than one proton (H + ) to the solution. Copyright©2000 by Houghton Mifflin Company. All rights reserved.11

14b–12 Copyright © Houghton Mifflin Company. All rights reserved.

Oxyacids and Organic Acids  Oxyacids are acids where the proton is attached to a oxygen.  Organic Acids are acids with a carbon backbone, with a carboxyl group attached.  Sulfuric Acid Copyright©2000 by Houghton Mifflin Company. All rights reserved.13 Acetic Acid

Acid Dissociation Constant (K a )  HA(aq) + H 2 O(l)  H 3 O + (aq) + A  (aq) Copyright©2000 by Houghton Mifflin Company. All rights reserved.14

Monoprotic Acids  Have one acidic proton.  Notice that strong acids do not have a K a ! Copyright©2000 by Houghton Mifflin Company. All rights reserved.15

14a–16 Copyright © 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).  H 2 O + H 2 O  H 3 O + + OH  conj conj acid base acid base  K w = 1  10  14 at 25°C Copyright©2000 by Houghton Mifflin Company. All rights reserved.17

 For any aqueous solution at 25°C the product of [H + ] and [OH - ] must equal 1 x  So this means that a soln:  [H+] = [OH-] is neutral  [H+] > [OH-] is acidic  [H+] < [OH-] is basic Copyright©2000 by Houghton Mifflin Company. All rights reserved.18

14.3 The pH Scale  Copyright©2000 by Houghton Mifflin Company. All rights reserved.19

pH and sig figs  [H+] = 1.0 x  pH = 9.00 Copyright©2000 by Houghton Mifflin Company. All rights reserved.20 2 sig figs 2 decimal places

Figure 14.9: pH meters are used to measure acidity. 14a–21 Copyright © Houghton Mifflin Company. All rights reserved.

Figure 14.8: The pH scale and pH values of some common substances.

14b–23 Copyright © Houghton Mifflin Company. All rights reserved.

Solving Weak Acid Equilibrium Problems 4 List major species in solution. 4 Choose species that can produce H + and write reactions. 4 Based on K values, decide on dominant equilibrium. 4 Write equilibrium expression for dominant equilibrium. 4 List initial concentrations in dominant equilibrium. Copyright©2000 by Houghton Mifflin Company. All rights reserved.24

Solving Weak Acid Equilibrium Problems (continued) 4 Define change at equilibrium (as “x”). 4 Write equilibrium concentrations in terms of x. 4 Substitute equilibrium concentrations into equilibrium expression. 4 Solve for x the “easy way.” 4 Verify assumptions using 5% rule. 4 Calculate [H + ] and pH. Copyright©2000 by Houghton Mifflin Company. All rights reserved.25

How does initial concentration affect percent dissociation?  Copyright©2000 by Houghton Mifflin Company. All rights reserved.26 Go to page 674

Figure 14.10: The effect of dilution on the percent dissociation and [H+] of a weak acid solution. 14b–27 Copyright © Houghton Mifflin Company. All rights reserved.

Percent Dissociation (Ionization) Copyright©2000 by Houghton Mifflin Company. All rights reserved.28

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)  weak = very little dissociation (or reaction with water)  H 3 CNH 2 (aq) + H 2 O(l)  H 3 CNH 3 + (aq) + OH  (aq) Copyright©2000 by Houghton Mifflin Company. All rights reserved.29

14b–30 Copyright © Houghton Mifflin Company. All rights reserved.

Acid-Base Properties of Salts Copyright©2000 by Houghton Mifflin Company. All rights reserved.31

14b–32 Copyright © Houghton Mifflin Company. All rights reserved.

Structure and Acid-Base Properties  Two factors for acidity in binary compounds: 4 Bond Polarity (high is good) 4 Bond Strength (low is good) Copyright©2000 by Houghton Mifflin Company. All rights reserved.33

14b–34 Copyright © Houghton Mifflin Company. All rights reserved.

Oxides  Acidic Oxides (Acid Anhydrides):  O  X bond is strong and covalent.  SO 2, NO 2, CrO 3  Basic Oxides (Basic Anhydrides):  O  X bond is ionic.  K 2 O, CaO Copyright©2000 by Houghton Mifflin Company. All rights reserved.35

Figure 14.11: The effect of the number of attached oxygens on the O—H bond in a series of chlorine oxyacids.

14b–37 Copyright © 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.38

Figure 14.12: Reaction of BF 3 with NH 3. 14b–39 Copyright © Houghton Mifflin Company. All rights reserved.

Figure 14.13: The Al(H 2 O) ion. 14b–40 Copyright © Houghton Mifflin Company. All rights reserved.