1

Chapter Learning Objectives

a. The chemical properties of acids and bases.

b. Acids and bases react with each other in a reaction known as neutralization.

c. Acids are proton (H+) donors; bases are proton acceptors that produce OH- in solution.

d. Learn some common acids and bases and their properties, such as their strengths.

e. The pH measures the acidity of a solution: pH < 7.0 is acidic; pH > 7.0 is basic; pH = 7.0 is neutral.

f. Buffers are important for maintaining our health.

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a. Acids

Arrhenius acids • produce H+ ions in water. H2O

HCl(g) H+(aq) + Cl- (aq)

• are electrolytes.• have a sour taste. • turn litmus red.• neutralize bases.

Hydronium ion – a hydrated proton, H3O+ = H+

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Names of Acids

• Acids with H and a nonmetal are named with the prefix hydro and end with ic acid.

HCl hydrochloric acid

• Acids with H and a polyatomic ion are named by changing the end of the name of the polyatomic ion from ate to ic acid or ite to ous acid.

ClO3− chlorate HClO3 chloric acid

ClO2− chlorite HClO2 chlorous acid

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Names of Some Common Acids

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Select the correct name for each of the following acids.A. HBr 1. bromic acid

2. bromous acid 3. hydrobromic acid

B. H2CO3 1. carbonic acid2. hydrocarbonic acid3. carbonous acid

C. HBrO2 1. bromic acid2. hydrobromous acid3. bromous acid

Learning Check

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A. HBr 3. hydrobromic acid

The name of an acid with H and one nonmetal uses the prefix hydro and ends with ic acid.

B. H2CO3 1. carbonic acid

An acid with H and a polyatomic ion is named by changing the end of an ate ion to ic acid.

C. HBrO2 3. bromous acid

This acid of bromite (BrO2-) is bromous acid.

Solution

7

a. Bases

Arrhenius bases • produce OH− ions in

water.• taste bitter or chalky.• are electrolytes.• feel soapy and slippery.• neutralize acids.

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Some Common Bases

Bases with OH- ions are named as the hydroxide of the metal in the formula.

NaOH sodium hydroxide

KOH potassium hydroxide

Ba(OH)2 barium hydroxide

Al(OH)3 aluminum hydroxide

Fe(OH)3 iron(III) hydroxide

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Match the formulas with the names.

A. ___HNO2 1) iodic acid

B. ___Ca(OH)2 2) sulfuric acid

C. ___H2SO4 3) sodium hydroxide

D. ___HIO3 4) nitrous acid

E. ___NaOH 5) calcium hydroxide

Learning Check

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Match the formulas with the names.

A. 4 HNO2 nitrous acid

B. 5 Ca(OH)2 calcium hydroxide

C. 2 H2SO4 sulfuric acid

D. 1 HIO3 iodic acid

E. 3 NaOH sodium hydroxide

Solution

11

Comparing Acids and Bases

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Identify each as a characteristic of an

A) acid or B) base.

____1. has a sour taste

____2. produces OH- in aqueous solutions

____3. has a chalky taste

____4. is an electrolyte

____5. produces H+ in aqueous solutions

Learning Check

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Identify each as a characteristic of an

A) acid or B) base.

A 1. has a sour taste

B 2. produces OH- in aqueous solutions

B 3. has a chalky taste

A, B 4. is an electrolyte

A 5. produces H+ in aqueous solutions

Solution

14

Definitions

Acidic Solutions – A solution that contains a higher concentration of H3O+ ions than OH- ions.

Basic Solutions (Alkaline solution) – A solution that contains a higher concentration of OH- ions than H3O+ ions

Salt – Ionic compounds composed of the cation from a base and the anion from an acid.

Neutralization Reaction – Reaction of equivalent quantities of an acid and a base

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In a neutralization reaction • an acid such as HCl reacts with a base such as NaOH.

HCl + H2O H3O+ + Cl−

NaOH Na+ + OH−

• the H3O+ from the acid and the OH− from the base form water.

H3O+ + OH− 2 H2O

b. Neutralization Reactions

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In the equation for neutralization, an acid and a base produce a salt and water.

acid base salt water

HCl + NaOH NaCl + H2O

2HCl + Ca(OH)2 CaCl2 + 2H2O

Neutralization Equations

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HCl(aq) + KOH(aq) H2O(aq) + KCl(aq)

Neutralization of H2O

H3O+ (aq) + OH- (aq) H2O(l) + H2O(l)

H2SO4(aq) + 2NaOH(aq) 2H2O(l) + Na2SO4(aq)

base

base

acid

acid water

water

salt

salt

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In water,• H+ is transferred from one H2O molecule to another. • one water molecule acts as an acid, while another

acts as a base.

H2O + H2O H3O+ + OH− .. .. .. .. :O: H + H:O: H:O:H + + :O:H−

.. .. .. .. H H H water water hydronium hydroxide

ion (+) ion (-)

Ionization of Water

Run the following web animations/movies. 9.3: The Autoionization of Water

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Pure Water is Neutral

In pure water, • the ionization of water

molecules produces small, but equal quantities of H3O+ and OH− ions.

• molar concentrations are indicated in brackets as [H3O+] and [OH−].

[H3O+] = 1.0 x 10−7 M

[OH−] = 1.0 x 10−7 MCopyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

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Acidic Solutions

Adding an acid to pure water • increases the [H3O+].

• cause the [H3O+] to exceed 1.0 x 10-7 M.

• decreases the [OH−].

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Basic Solutions

Adding a base to pure water

• increases the [OH−].

• causes the [OH−] to exceed 1.0 x 10− 7M.

• decreases the [H3O+].

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

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Comparison of [H3O+] and [OH−]

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The ion product constant, Kw, for water

• is the product of the concentrations of the hydronium and hydroxide ions.

Kw = [ H3O+] [ OH− ]

• can be obtained from the concentrations in pure water.

Kw = [ H3O+] [ OH− ]

Kw = [1.0 x 10− 7 M] x [ 1.0 x 10− 7 M]

= 1.0 x 10− 14

Ion Product of Water, Kw

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[H3O+] and [OH−] in Solutions

In neutral, acidic, or basic solutions, the Kw is always 1.0 x 10−14.

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Guide to Calculating [H3O+]

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Calculating [H3O+]

What is the [H3O+] of a solution if [OH−] is 5.0 x 10-8 M?

STEP 1: Write the Kw for water.

Kw = [H3O+ ][OH− ] = 1.0 x 10−14

STEP 2: Rearrange the Kw expression.

[H3O+] = 1.0 x 10-14

[OH−]

STEP 3: Substitute [OH−]. [H3O+] = 1.0 x 10-14 = 2.0 x 10-7 M

5.0 x 10- 8

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If lemon juice has [H3O+] of 2 x 10−3 M, what is the [OH−] of the solution?

1) 2 x 10−11 M

2) 5 x 10−11 M

3) 5 x 10−12 M

Learning Check

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3) 5 x 10−12 M

Rearrange the Kw to solve for [OH- ]

Kw = [H3O+ ][OH− ] = 1.0 x 10−14

[OH− ] = 1.0 x 10 -14 = 5 x 10−12 M 2 x 10 - 3

Solution

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The [OH−] of an ammonia solution is 4.0 x 10−2 M. What is the [H3O+ ] of the solution?

1) 2.5 x 10− 11 M

2) 2.5 x 10−12 M

3) 2.5 x 10−13 M

Learning Check

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3) 2.5 x 10−13 M

[ H3O+] = 1.0 x 10−14 = 2.5 x 10−13 M

4.0 x 10−2

Solution

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c. BrØnsted-Lowry Acids and Bases

According to the BrØnsted-Lowry theory,• acids donate a proton (H+). • bases accept a proton (H+).

Run the following web animations/movies.

9.1: Proton Transfer with an Acid & a Base

9.2: Reacting with Water

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NH3, a BrØnsted-Lowry Base

In the reaction of ammonia and water,

• NH3 is the base that accept H+.

• H2O is the acid that donates H+.

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• A strong acid completely ionizes (100%) in aqueous solutions.HCl(g) + H2O(l) H3O+ (aq) + Cl− (aq)

• A weak acid dissociates only slightly in water to form a few ions in aqueous solutions.

H2CO3(aq) + H2O(l) H3O+(aq) + HCO3− (aq)

d. Strengths of Acids

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Strong Acids

In water, the dissolved

molecules of a strong

acid

• dissociate into ions.• give large

concentrations of H3O+

and the anion (A-).

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

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Weak Acids

In weak acids,

• only a few molecules dissociate.

• most of the weak acid remains as the undissociated (molecular) form of the acid.

• the concentrations of the H3O+

and the anion (A-) are small.Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

HA(aq) + H2O(l) H3O(aq) + A−(aq)

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Strong and Weak Acids

• In an HCl solution, the strong acid HCl dissociates 100%.

• A solution of the weak acid CH3COOH contains mostly molecules and a few ions.

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Strong acids• make up six of all the acids. • have weak conjugate bases.

Strong Acids

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Weak Acids

Weak acids• make up most of the acids. • have strong conjugate bases.

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Comparing Strong and Weak Acids

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Strong Bases

Strong bases

• are formed from metals of Groups 1A (1) and 2A (2).

• include LiOH, NaOH, KOH, and

Ca(OH)2.

• dissociate completely in water.

KOH(s) K+(aq) + OH−(aq)

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Weak Bases

Weak bases

• are most other bases.

• dissociate only slightly in water.

• form only a few ions in water.

NH3(g) + H2O(l) NH4+(aq) + OH−(aq)

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Learning Check

Identify each of the following as a strong or weak acid or base.

A. HBr

B. HNO2

C. NaOH

D. H2SO4

E. Cu(OH)2

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Solution

Identify each of the following as a strong or weak acid or base.

A. HBr strong acid

B. HNO2 weak acid

C. NaOH strong base

D. H2SO4 strong acid

E. Cu(OH)2 weak base

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Learning Check

Identify the stronger acid in each pair.

1. HNO2 or H2S

2. HCO3− or HBr

3. H3PO4 or H3O+

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Solution

Identify the stronger acid in each pair.

1. HNO2

2. HBr

3. H3O+

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Molarity (M)

Molarity (M) is

• a concentration term for solutions.

• gives the moles of solute in 1 L solution.

• moles of soluteliter of solution

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What is the molarity of 0.500 L NaOH solution if itcontains 6.00 g NaOH?

STEP 1 Given 6.00 g NaOH in 0.500 L solution Need molarity (mole/L)

STEP 2 Plan g NaOH mole NaOH molarity

Calculation of Molarity

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Calculation of Molarity (cont.)

STEP 3 Conversion factors 1 mole NaOH = 40.0 g1 mole NaOH and 40.0 g NaOH40.0 g NaOH 1 mole NaOH

STEP 4 Calculate molarity.6.00 g NaOH x 1 mole NaOH = 0.150 mole

40.0 g NaOH 0.150 mole = 0.300 mole = 0.300 M NaOH

0.500 L 1 L

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What is the molarity of 325 mL of a solution containing 46.8 g of NaHCO3?

1) 0.557 M

2) 1.44 M

3) 1.71 M

Learning Check

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3) 1.71 M

46.8 g NaHCO3 x 1 mole NaHCO3 = 0.557 mole NaHCO3

84.0 g NaHCO3

0.557 mole NaHCO3 = 1.71 M NaHCO3

0.325 L

Solution

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e. pH Scale

The pH of a solution

• is used to indicate the acidity of a solution.

• has values that usually range from 0 to 14.

• is acidic when the values are less than 7.

• is neutral with a pH of 7.

• is basic when the values are greater than 7.

A pH Meter

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pH of Everyday Substances

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

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Identify each solution as

1) acidic 2) basic 3) neutral

A. ___ HCl with a pH = 1.5

B. ___ pancreatic fluid [H3O+] = 1 x 10−8 M

C. ___ Sprite® soft drink pH = 3.0

D. ___ pH = 7.0

E. ___ [OH−] = 3 x 10−10 M

F. ___ [H3O+ ] = 5 x 10−12

Learning Check

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A. 1 HCl with a pH = 1.5

B. 2 Pancreatic fluid [H3O+] = 1 x 10−8 M

C. 1 Sprite® soft drink pH = 3.0

D. 3 pH = 7.0

E. 1 [OH-] = 3 x 10−10 M

F. 2 [H3O+] = 5 x 10−12

Solution

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Testing the pH of Solutions

The pH of solutions can be determined using • a) pH meter• b) pH paper• c) indicators that have specific colors at different pH values.

Run the following web animations/movies.

9.4a: Detecting Acid-Base Rxns Using a pH Meter

9.4b: pH Changes using HCl to Water

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pH is the negative log of the hydronium ion concentration.

pH = - log [H3O+]

Example: For a solution with [H3O+] = 1 x 10−4

pH = −log [1 x 10−4 ]

pH = - [-4.0]

pH = 4.0

Note: The number of decimal places in the pH equals

the significant figures in the coefficient of [H3O+].

4.0

1 SF in 1 x 10-4

Calculating pH

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Guide to pH Calculations

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Significant Figures in pH

When expressing log values, the number of decimal

places in the pH is equal to the number of significant

figures in the coefficient of [H3O+].

[H3O+] = 1 x 10-4 pH = 4.0

[H3O+] = 8.0 x 10-6 pH = 5.10

[H3O+] = 2.4 x 10-8 pH = 7.62

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Find the pH of a solution with a [H3O+] of 1.0 x 10−3:

STEP 1 Enter [H3O+]

Enter 1 x 10-3 by pressing 1 (EE) 3

The EE key gives an exponent of 10 and

change sign (+/- key or – key)

STEP 2 Press log key and change sign

- log (1 x 10−3) = -[-3]

STEP 3 Adjust figures after decimal point to equal the

significant figures in the coefficient.

3 3.00 Two significant figures in 1.0 x 10−3

Calculating pH

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Learning Check

What is the pH of coffee if the [H3O+] is 1 x 10−5 M?

1) pH = 9.0

2) pH = 7.0

3) pH = 5.0

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Solution

What is the pH of coffee if the [H3O+] is 1 x 10−5M?

3) pH = 5.0

pH = -log [1 x 10−5] = -(-5.0) = 5.0

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A. The [H3O+] of tomato juice is 2 x 10−4 M.

What is the pH of the solution?

1) 4.0 2) 3.7 3) 10.3

B. The [OH−] of a solution is 1.0 x 10−3 M.

What is the pH of the solution?

1) 3.00 2) 11.00 3) -11.00

Learning Check

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A. 2) 3.7pH = - log [ 2 x 10-4] = 3.7

2 (EE) 4 (+/-) log (+/-)

B. 2) 11.00 Use the Kw to obtain [H3O+] = 1.0 x 10 −11

pH = - log [1.0 x 10 −11] 1.0 (EE) 11 (+/-) log (+/-)

Solution

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[H3O+], [OH-], and pH Values

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

65

Calculating [H3O+] from pH

The [H3O+] can be expressed by using the pH as the negative power of 10.

[H3O+] = 1 x 10 -pH

For pH = 3.0, the [H3O+] = 1 x 10 -3

On a calculator

1. Enter the pH value 3.0

2. Change sign -3.0

3. Use the inverse log key (or 10x) to obtain

the [H30+]. = 1 x 10 -3 M

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A. What is the [H3O+] of a solution with a pH of 10.0? 1) 1 x 10−4 M 2) 1 x 1010 M 3) 1 x 10−10 M

B. What is the [OH−] of a solution with a pH of 2.00? 1) 1.0 x 10− 2 M 2) 1.0 x 10−12 M 3) 2.0 M

Learning Check

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A. What is the [H3O+] of a solution with a pH of 10.0?

3) 1 x 10-10 M 1 x 10-pH

B. What is the [OH−] of a solution with a pH of 2.00? 2) 1.0 x 10−12 M

[H3O+] = 1.0 x 10−2 M 1 x 10-pH

[OH−] = 1.0 x 10−14 = 1.0 x 10−12 M 1.0 x 10−2 M

Solution

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f. Buffers

When an acid or base is added

• to water, the pH changes drastically.

• to a buffer solution, the pH is maintained; pH does not change.

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Buffers

• resist changes in pH from the addition of acid or base.

• in the body, absorb H3O+ or OH- from foods and cellular processes to maintain pH.

• are important in the proper functioning of cells.

• in blood maintain a pH close to 7.4. A change in the pH of the blood affects the uptake of oxygen and therefore cellular processes.

Buffers

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A buffered solution• contains a combination of acid-base conjugate pairs.• may contain a weak acid and a salt of its conjugate

base. • typically has equal concentrations of a weak acid

and its salt.• may also contain a weak base and a salt of the

conjugate acid.

Components of a Buffer

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In the acetic acid/acetate buffer with acetic acid

(CH3COOH) and sodium acetate (CH3COONa)

• The salt produces acetate ions and sodium ions.

CH3COONa(aq) CH3COO-(aq) + Na+ (aq)

• The salt is added to provide a higher concentration of the conjugate base CH3COO- than the weak acid alone.

CH3COOH(aq) + H2O(l) CH3COO-(aq) + H3O+(aq) Large amount Large amount

Buffer Action

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Key Words

Acid Base Indicator Hydronium ion (H3O+)

Polyprotic acid Strong acid Weak acid Alkali Hydroxide ion (OH-)

pH meter Strong base Weak base Amphoteric pH Neutral solution Conjugate acid-base

pair Buffer Neutralization