Common household substances that contain acids and bases. Vinegar is a dilute solution of acetic acid. Drain cleaners contain strong bases such as sodium

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–1Copyright © Houghton Mifflin Company. All rights

reserved.

14b–2Copyright © 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 + H2O Cl + H3O+

acid base

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 3

Conjugate Acid/Base Pairs

HA(aq) + H2O(l) H3O+(aq) + A(aq) conj conjacid 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.


Figure 14.1: The reaction of HCl and H2O.


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Base Acid conj. acid conj. base

14.2 Acid Strength

Its equilibrium position lies far to the right. (HNO3)

Yields a weak conjugate base. (NO3)


Strong Acid:Strong Acid:

Acid Strength(continued)

Its equilibrium lies far to the left. (CH3COOH)

Yields a much stronger (it is relatively strong) conjugate base than water. (CH3COO)


Weak Acid: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.


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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 relationship of acid strength and conjugate base strength for the reaction

Polyprotic Acids

. . . can furnish more than one proton (H+) to the solution.


H CO H HCO ( )

HCO H CO ( )

2 3 3 a

3 32

a

1

2

K

K


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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


Acid Dissociation Constant (Ka)

HA(aq) + H2O(l) H3O+(aq) + A(aq)


Ka3H O A

HA

H A

HA

Monoprotic Acids

Have one acidic proton. Notice that strong acids do not have a

Ka!



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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 base acid base

Kw = 1 1014 at 25°C


For any aqueous solution at 25°C the product of [H+] and [OH-] must equal 1 x 10-14.

So this means that a soln: [H+] = [OH-] is neutral [H+] > [OH-] is acidic [H+] < [OH-] is basic


14.3 The pH Scale


pH and sig figs

[H+] = 1.0 x 10-9

pH = 9.00


2 sig figs

2 decimal places

Figure 14.9: pH meters are used to measure acidity.


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


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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.


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.


How does initial concentration affect percent

dissociation?


Go to page 674

Figure 14.10: The effect of dilution on the percent dissociation and [H+] of a weak acid solution.


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Percent Dissociation (Ionization)

% dissociationamount dissociated( )initial concentration( )

100% MM


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)H3CNH2(aq) + H2O(l) H3CNH3

+(aq) + OH(aq)



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Acid-Base Properties of Salts

Cation AnionAcidic

or Basic Exampleneutral neutral neutral NaCl

neutral conj base ofweak acid

basic NaF

conj acid ofweak base

neutral acidic NH4Cl

conj acid ofweak base

conj base ofweak acid

depends onKa & Kb

values

Al2(SO4)3



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Structure and Acid-Base Properties

Two factors for acidity in binary compounds:

Bond Polarity (high is good)

Bond Strength (low is good)



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Oxides

Acidic Oxides (Acid Anhydrides): OX bond is strong and covalent.

SO2, NO2, CrO3

Basic Oxides (Basic Anhydrides): OX bond is ionic.

K2O, CaO


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


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Lewis Acids and Bases

Lewis Acid: electron pair acceptor Lewis Base: electron pair donor


Al3+ + 6H

OH

Al OH

H6

3+

Figure 14.12: Reaction of BF3 with NH3.


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Figure 14.13: The Al(H2O)6

3+ ion.


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Documents

Common household substances that contain acids and bases. Vinegar is a dilute solution of acetic acid. Drain cleaners contain strong bases such as sodium