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1Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Chapter 10 Acids and Bases
10.1 Acids and Bases10.2 Conjugate Acid-Base Pairs10.3 Strengths of Acids and Bases10.4 Dissociation Constants10.5 Ionization of Water10.6 The pH Scale10.7 Reactions of Acids and Bases
(just neutralization reactions)10.9 Buffers
2Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Arrhenius acids Produce H+ ions in water.
H2OHCl H+(aq) + Cl– (aq)
Are electrolytes. Have a sour taste. Corrode metals. React with bases to form salts
and water.
10.1 Acids
Examples:
Vinegar (5% acetic acid)
Citric acid (fruits)
Ascorbic acid (vitamin C)
Lactic acid (in muscles)
Phosphoric acid (Coke)
3Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Arrhenius bases Produce OH– ions in
water. Taste bitter or chalky. Are electrolytes. Feel soapy and slippery. React with acids to form
salts and water.
Bases
Examples:
Draino (NaOH)
Baking Soda (NaHCO3)
Bleach (NaOCl)
Ammonia (NH3)
Antacid
4Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Comparing Acids and Bases
2
5Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
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
6Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
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
7Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Names of Acids
Acids with H and one nonmetal are namedwith the prefix hydro- and end with -ic acid.HCl hydrochloric acid
Acids with H and a polyatomic ion arenamed by changing the end of an –ate ionto -ic acid and an –ite ion to -ous acid.
HClO3 chloric acid
HClO2 chlorous acid
8Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Some Acids and Their Anions
3
9Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Name each of the following as acids:A. HBr 1. bromic acid
2. bromous acid3. hydrobromic acid
B. H2CO3 1. carbonic acid2. hydrocarbonic acid3. carbonous acid
Learning Check
10Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
A. HBr 3. hydrobromic acid
The name of an acid with H and one nonmetalbegins with the prefix hydro- and ends with -icacid.
B. H2CO3 1. carbonic acid
An acid with H and a polyatomic ion is namedby changing the end of an –ate ion to -ic acid.
Solution
11Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Bases with OH- ions are named as thehydroxide 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
Some Common Bases
12Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Match the formulas with the names:
A. ___ HNO2 1) hydrochloric acid
B. ___Ca(OH)2 2) sulfuric acid
C. ___H2SO4 3) sodium hydroxide
D. ___HCl 4) nitrous acid
E. ___NaOH 5) calcium hydroxide
Learning Check
4
13Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Match the formulas with the names:A. 4 HNO2 4) nitrous acid
B. 5 Ca(OH)2 5) calcium hydroxide
C. 2 H2SO4 2) sulfuric acid
D. 1 HCl 1) hydrochloric acid
E. 3 NaOH 3) sodium hydroxide
Solution
14Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
According to the Brønsted-Lowry theory,
Acids are hydrogen ion (H+) donors.
Bases are hydrogen ion (H+) acceptors.
donor acceptor hydronium ion
HCl + H2O H3O+ + Cl-
+ -
+ +
Johannes BrØnsted and Thomas Lowry (1923)
15Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
When NH3 dissolves in water, a few NH3molecules react with water to form ammoniumion NH4
+ and a hydroxide ion.
NH3 + H2O NH4+(aq) + OH- (aq)
acceptor donor
+ - + +
NH3, A Bronsted-Lowry Base
16Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
10.2 Conjugate Acids and Bases
An acid that donates H+ forms a conjugate base. A base that accepts a H+ forms a conjugate acid. In an acid-base reaction, there are two conjugate
acid-base pairs.
acid 1 conjugate base 1
+ +
base 2 conjugate acid 2
HF H2O H3O+ F-
5
17Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Conjugate Acid-Base Pairs
A conjugate acid-base pair is two substancesrelated by a loss or gain of H+.
+ +
acid 1– conjugate base 1
base 2– conjugate acid 2
HF H2O H3O+ F-
HF, F-
H2O, H3O+
18Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Learning Check
A. Write the conjugate base of the following:
1. HBr
2. H2S
3. H2CO3
B. Write the conjugate acid of the following:
1. NO2–
2. NH3
3. OH–
19Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Solution
A. Write the conjugate base of the following:
1. HBr Br-
2. H2S HS–
3. H2CO3 HCO3–
B. Write the conjugate acid of the following:
1. NO2– HNO2
2. NH3 NH4+
3. OH– H2O
20Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Learning Check
Identify the following that are acid-baseconjugate pairs.
1. HNO2, NO2–
2. H2CO3, CO32 –
3. HCl, ClO4 –
4. HS–, H2S
5. NH3, NH4+
6
21Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Solution
Identify the following that are acid-baseconjugate pairs.
1. HNO2, NO2–
4. HS–, H2S
5. NH3, NH4+
22Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Learning Check
A. The conjugate base of HCO3– is
1. CO32– 2. HCO3
– 3. H2CO3
B. The conjugate acid of HCO3– is
1. CO32– 2. HCO3
– 3. H2CO3
C. The conjugate base of H2O is
1. OH– 2. H2O 3. H3O+
D. The conjugate acid of H2O is
1. OH– 2. H2O 3. H3O+
23Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Solution
A. The conjugate base of HCO3 – is
1. CO32–
B. The conjugate acid of HCO3– is
3. H2CO3
C. The conjugate base of H2O is
1. OH–
D. The conjugate acid of H2O is 3. H3O+
24Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Strong acids completely ionize (100%) inaqueous solutions.HCl + H2O H3O+ (aq) + Cl– (aq)
(100 % ions) Strong bases completely (100%) dissociate
into ions in aqueous solutions. H2O
NaOH Na+ (aq) + OH–(aq) (100 % ions)
10.3 Strengths of Acids and Bases
7
25Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Strong and Weak Acids
In an HCl solution,the strong acid HCldissociates 100%.
A solution of theweak acidCH3COOH containsmostly moleculesand a few ions.
26Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Only a few acids are strong acids.
The conjugate bases of strong acids are weakbases.
Strong Acids
27Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Most acids are weak acids. The conjugatebases of weak acids are strong bases.
Weak Acids
28Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Most bases in Groups 1A and 2A arestrong bases. They include
LiOH, NaOH, KOH, and Ca(OH)2
Most other bases are weak bases.
Strong Bases
8
29Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Learning Check
Identify each of the following as a strong orweak acid or base.
A. HBr
B. HNO2
C. NaOH
D. H2SO4
E. Cu(OH)2
30Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Solution
Identify each of the following as a strong orweak 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
31Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Learning Check
A. Identify the stronger acid in each pair. 1. HNO2 or H2S 2. HCO3
– or HBr 3. H3PO4 or H3O+
B. Identify the strong base in each pair. 1. NO3
– or F-
2. CO32– or NO2
–
3. OH– or H2O
32Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Solution
A. Identify the stronger acid in each pair. 1. HNO2
2. HBr 3. H3O+
B. Identify the stronger base in each pair. 1. F-
2. CO32–
3. OH–
9
33Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Equilibrium
H2SO4 + H2O H3O+ + HSO4-
stronger stronger weaker weaker acid base acid base
CO3- + H2O HCO3
- + OH-
weaker weaker stronger stronger base acid acid base
34Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
10.4 Strong Acids
In water, thedissolved moleculesof a strong acid areessentially allseparated into ions.
The concentrationsof H3O+ and theanion (A–) arelarge.
35Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Weak Acids
In weak acids, The equilibrium
favors theundissociated(molecular) form ofthe acid.
The concentrationsof the H3O+ and theanion (A–) aresmall.
36Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Dissociation Constants
In a weak acid, the rate of the dissociation ofthe acid is equal to the rate of the association.
HA + H2O H3O+ + A–
The equilibrium expression for a weak acid is
Keq = [H3O+][A-]
[HA][H2O]
10
37Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Acid Dissociation Constants (Ka)
The [H2O] is large and remains unchanged.It is combined with the Keq to write the aciddissociation constant, Ka.
Ka = Keq[H2O] = [H3O+][A-]
[HA]
38Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Writing Ka for a Weak Acid
Write the Ka for H2S.
1. Write the equation for the dissociation of H2S.
H2S + H2O H3O+ + HS–
2. Set up the Ka expression
Ka = [H3O+][HS-]
[H2S]
39Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Learning Check
Write the Ka for HCN.
40Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Solution
Write the Ka for HCN.
Write the equation for the dissociation of HCN.
HCN + H2O H3O+ + CN–
Set up the Ka expression
Ka = [H3O+][CN–]
[HCN]
Note: Ka = Keq [H2O]
11
41Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Acid dissociation constants
Larger Ka (stronger acid)
Larger Kb (stronger base)
Smaller Ka (weaker acid)
Smaller Kb (weaker base)
42Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
In water, H+ is transferred from one H2O moleculeto another.
One water molecule acts as an acid, while anotheracts as a base (amphiprotic).H2O + H2O H3O+ + OH –
.. .. .. .. :O: H + :O:H H:O:H + + :O:H–
.. .. .. .. H H H water molecules hydronium hydroxide
ion (+) ion (–)
10.5 Ionization of Water
43Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
In pure water, the ionization ofmolecules produces small, butequal quantities of H3O+ and OH-
ions.H2O + H2O H3O+ + OH-
Molar concentrations areindicated as [H3O+] and [OH-].[H3O+] = 1.0 x 10-7 M[OH-] = 1.0 x 10-7 M
Pure Water is Neutral
44Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Adding an acid to purewater increases the[H3O+].
In acids, [H3O+] exceeds1.0 x 10–7 M.
As [H3O+] increases,[OH–] decreases.
Acidic Solutions
12
45Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Adding a base to purewater increases the[OH–].
In bases, [OH–]exceeds 1.0 x 10–7M.
As [OH–] increases,[H3O+] decreases.
Basic Solutions
46Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Comparison of [H3O+] and [OH–]
47Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
The ion product constant, Kw, for water isthe product of the concentrations of thehydronium and hydroxide ions.
Kw = [H3O+][OH–] We can obtain the value of Kw using the
concentrations in pure water. Kw = [1.0 x 10–7][1.0 x 10–7]
= 1.0 x 10–14
Ion Product of Water, Kw
48Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Kw in Acids and Bases
In neutral, acidic, and basic solutions, theKw is equal to 1.0 x 10–14.
13
49Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
What is the [H3O+] of a solution if [OH–] is1.0 x 10-8
M?
Rearrange the Kw expression for [H3O+ ].
Kw = [H3O+][OH–] = 1.0 x 10-14
[H3O+] = 1.0 x 10-14
[OH–]
[H3O+] = 1.0 x 10-14 = 1.0 x 10-6 M 1.0 x 10- 8
Calculating [H3O+]
50Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
The [H3O+] of lemon juice is 1.0 x 10–3 M.
What is the [OH–] of the solution?
1) 1.0 x 103 M
2) 1.0 x 10–11 M
3) 1.0 x 1011 M
Learning Check
51Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
The [H3O+] of lemon juice is 1.0 x 10–3 M.What is the [OH–] of the solution?
2) 1.0 x 10–11 M
Rearrange the Kw to solve for [OH–]
Kw = [H3O+ ][OH–] = 1.0 x 10–14
[OH- ] = 1.0 x 10 -14 = 1.0 x 10 !–11 M 1.0 x 10 - 3
Solution
52Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
The [OH–] of a solution is 5 x 10–2 M.What is the [H3O+ ] of the solution?
1) 2 x 10–2 M
2) 1 x 102 M
3) 2 x 10–13 M
Learning Check
14
53Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
The [OH–] of a water solution is 5 x 10–2 M.
What is the [H3O+] of the solution?
3) 2 x 10–13 M
[ H3O+] = 1.0 x 10 –14
5 x 10–2
Solution
54Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
A. What is the [OH–] if the [H3O+ ] is 1 x 10–4 M?Identify the solution as acidic, basic, or neutral.1) 1 x 10–6 M 2) 1 x 10–8 M 3) 1 x 10–10 M
B. What is [H3O+] if the [OH–] is 5 x 10–9 M?Identify the solution as acidic, basic, or neutral.1) 1 x 10–6 M 2) 2 x 10–6 M 3) 2 x 10–7 M
Learning Check
55Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Kw = [H3O+][OH–] = 1.0 x 10 14
A. 3) [OH–] = 1.0 x 10–14 = 1.0 x 10–10
1.0 x 10–4 acidic
B. 2) [H3O+] = 1.0 x 10–14 = 2 x 10–6
5 x 10–9 acidic
Solution
56Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
10.6 pH Scale
The pH scale:
Is used to indicate the acidity of a solution.
Has values that usually range from 0 to 14.
Indicates an acidic solution when the valuesare less than 7.
Indicates a neutral solution with a pH of 7.
Indicates a basic solution when the valuesare greater than 7.
15
57Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Neutral
[H3O+]>[OH-] [H3O
+] = [OH-] [H3O+]<[OH-]
Acidic Basic
pH Range
58Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
59Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Identify each solution as1. acidic 2. basic 3. neutralA. ___ HCl with a pH = 1.5B. ___ Pancreatic fluid [H3O+] = 1 x 10–8 MC. ___ Sprite soft drink pH = 3.0D. ___ pH = 7.0E. ___ [OH– ] = 3 x 10–10 MF. ___ [H3O+ ] = 5 x 10–12
Learning Check
60Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Identify each solution as
1. acidic 2. basic 3. neutral
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
16
61Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Testing the pH of Solutions
The pH of solutions can be determined using aa) pH meter, b) pH paper, and c) indicatorsthat have specific colors at different pHs.
62Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
mx = n, then logm n = x, m = 10
Ordinarily log10 (log in calculator)
log10 100 = 2.000 (102 = 100)
log10 1 = 0.000 (100 = 1)
log10 0.001 = -3.000 (10-3 = 0.001)
Logarithms (log)
63Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
1. Count the significant digits in the number (n)(log n = x )
2. Add that same number of decimal points to thelog of the number (x).
Example: log10 2.00 = 0.301log10 2.0 = 0.30log10 2 = 0.3log10 2.0 x 103 = 3.30
Logarithms (log) Sig Figs
64Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
pH is:
Defined as the negative log of the hydrogenion concentration.
pH = - log [H3O+]
The value of the negative exponent of [H3O+]for concentrations with a coefficient of 1.
[H3O+] = 1 x 10-4 pH = 4.0
[H3O+] = 1 x 10-11 pH = 11.0
pH Scale
17
65Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
A calculator can be used to find the pH of asolution with a [H3O+] of 1 x 10-3 as follows.1. Enter 1 x 10-3 by pressing 1 (EE) 3 (+/–). The EE key gives an exponent of 10 and the +/– key
changes the sign.2. Press the log key to obtain log 1 x 10-3. log (1 x 10-3) = –33. Press the +/– key to multiply by –1. (-3) +/– = 3
Calculations of pH
66Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Significant Figures in pH
When expressing log values, the number of decimalplaces in the pH is equal to the number ofsignificant figures in the coefficient of [H3O+].
[H3O+] = 1 x 10-4 pH = 4.0
[H3O+] = 1.0 x 10-6 pH = 6.00
[H3O+] = 2.4 x 10-8 pH = 7.62
67Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
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
68Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
A. 2) 3.7 pH = – 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] = – 11.00 (+/–) = 11.00
Solution
18
69Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Calculating [H3O+] from pH
The [H3O+] can be expressed with the pH asthe negative power of 10.[H3O+] = 1 x 10-pH
If the pH is 3.0, the [H3O+] = 1 x 10-3
On a calculator1. Enter the pH value 3.02. Use (+/–) to change sign 3.0 (+/–) = –3.03. Use the inverse log key (or 10x) to obtain
the [H30+]. = 1 x 10-3 M70Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
A. What is the [H3O+] of a solution with apH of 10.0? 1) 1 x 10 -4 M 2) 1 x 1010 M 3) 1 x 10 -10 M
B. What is the [H3O+] of a solution with apH of 5.7? 1) 2 x 10- 6 M 2) 5 x 105 M 3) 1 x 10-5 M
Learning Check
71Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
A. What is the [H3O+] of a solution with a pHof 10.0? 3) 1 x 10-10 M 1 x 10-pH
B. What is the [H3O+] of a solution with a pHof 5.7? 1) 2 x 10- 6 M
5.7 (+/–) inv log (or 10x) = 2 x 10-6
Solution
72Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
pOH
The pOH of a solution:
Is related to the [OH-].
Is similar to pH.
pOH = – log [OH-]
Added to the pH value is equal to 14.0.
pH + pOH = 14.0
19
73Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
pH and pOH
The sum of thepH and pOHvalues is equal to14.0 for anyaqueoussolution.
74Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Learning Check
What is the pH and the pOH of coffeeif the [H3O+] is 1 x 10-5 M?
1) pH = 5.0 pOH =7.0
2) pH = 7.0 pOH = 9.0
3) pH = 5.0 pOH = 9.0
75Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Solution
What is the pH and the pOH of coffee if the [H3O+]is 1 x 10-5 M?
3) pH = 5.0 pOH = 9.0
pH = – log [1 x 10-5] = –(– 5.0) = 5.0
pH + pOH = 14.0
pOH = 14.0 – pH = 14.0 – 5.0 = 9.0
or [OH-] = 1 x 10-9
pOH = – log [1 x 10-9] = –(– 9.0) = 9.0
76Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
An acid such as HCl produces H3O+ and a basesuch as NaOH provides OH-.HCl + H2O H3O+ + Cl-
NaOH Na+ + OH-
In a neutralization reaction, the H3O+ and the OH-
combine to form water. H3O+ + OH- 2 H2O
The positive ion (metal) and the negative ion(nonmetal) are the ions of a salt.
10.7 Neutralization Reactions
20
77Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
In the equation for neutralization, an acidand a base produce a salt and water.
NaOH + HCl NaCl + H2O
base acid salt water
Ca(OH)2 + 2 HCl CaCl2 + 2H2O base acid salt water
Neutralization Equations
78Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Write the balanced equation for the neutralizationof magnesium hydroxide and nitric acid.
1. Write the formulas of the acid and base.Mg(OH)2 + HNO3
2. Balance to give equal OH- and H+.
Mg(OH)2 + 2 HNO3
3. Write the products (a salt and water) and balance: Mg(OH)2 + 2HNO3 Mg(NO3)2 + 2H2O
Balancing NeutralizationReactions
79Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Write strong acids, bases, and salts as ions.
H+ + Cl- + Na+ + OH- Na+ + Cl- + H2O
Cross out matched ions.
H+ + Cl- + Na+ + OH- Na+ + Cl- + H2O
Write a net ionic reaction.
H+ + OH- H2O
Ionic Equations for Neutralization
80Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Select the correct group of coefficients for the
following neutralization equations.
A. __ HCl + __ Al(OH)3 __AlCl3 + __ H2O
1) 1, 3, 3, 1 2) 3, 1, 1, 1 3) 3, 1, 1 3
B. __ Ba(OH)2 + __H3PO4 __Ba3(PO4)2 + __ H2O
1) 3, 2, 2, 2 2) 3, 2, 1, 6 3) 2, 3, 1,
Learning Check
21
81Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
A. 3) 3, 1, 1 3
3HCl + 1Al(OH)3 1AlCl3 + 3H2O
B. 2) 3, 2, 1, 6
3Ba(OH)2 + 2H3PO4 1Ba3(PO4)2 + 6H2O
Solution
82Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Antacids neutralize stomach acid (HCl). Alka-Seltzer NaHCO3, citric acid, aspirin Chooz, Tums CaCO3
Di-gel CaCO3 and Mg(OH)2
Gelusil, Maalox, Al(OH)3 and Mg(OH)2
Mylanta Milk of Magnesia Mg(OH)2
Rolaids AlNa(OH)2CO3
Antacids
83Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Learning Check
Write the neutralization reactions forstomach acid HCl and Mylanta.
84Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Solution
Write the neutralization reactions for stomachacid HCl and Mylanta.Mylanta: Al(OH)3 and Mg(OH)2
3HCl + Al(OH)3 AlCl3 + 3H2O
2HCl + Mg(OH)2 MgCl2 + 2H2O
22
85Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
When an acid orbase is added towater, the pHchangesdrastically.
A buffer solutionresists a change inpH when an acidor base is added.
10.9 Buffers
86Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Buffers
Absorb H3O+ or OH- from foods andcellular processes to maintain pH.
Are important in the proper functioning ofcells and blood.
In blood maintain a pH close to 7.4. Achange in the pH of the blood affects theuptake of oxygen and cellular processes.
Buffers
87Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
A buffer solution Contains a combination of acid-base conjugate
pairs. Contains a weak acid and a salt of the
conjugate base of that acid. Typically has equal concentrations of a weak
acid and its salt. May also contain a weak base and a salt with
the conjugate acid.
Components of a Buffer
88Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
The acetic acid/acetate buffer contains aceticacid (CH3COOH) and sodium acetate(CH3COONa).
The salt produces sodium and acetate ions.CH3COONa CH3COO- + Na+
The salt provides a higher concentration of theconjugate base CH3COO- than the weak acid.CH3COOH + H2O CH3COO- + H3O+
Large amount Large amount
Buffer Action
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The function of the weak acid is to neutralize abase. The acetate ion in the product adds to theavailable acetate.
CH3COOH + OH– CH3COO– + H2O
Function of the Weak Acid
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The function of the acetate ion CH3COO-
(conjugate base) is to neutralize H3O+ from acids.The weak acid product adds to the weak acidavailable.
CH3COO- + H3O+ CH3COOH + H2O
Function of the Conjugate Base
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The weak acid in a buffer neutralizes base.
The conjugate base in the buffer neutralizes acid.
The pH of the solution is maintained.
Summary of Buffer Action
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Learning Check
Does each combination make a buffer solution? 1) yes 2) no Explain.
A. HCl and KCl
B. H2CO3 and NaHCO3
C. H3PO4 and NaCl
D. CH3COOH and CH3COOK
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Solution
Does each combination make a buffer solution?
1) yes 2) no Explain.
A. HCl + KCl no; HCl is a strong acid.
B. H2CO3 + NaHCO3 yes; weak acid and its salt.
C. H3PO4 + NaCl no; NaCl does not contain a conjugate base of H3PO4.
D. CH3COOH + CH3COOK
yes; weak acid and its salt.
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pH of a Buffer
The [H3O+] in the Ka expression is used todetermine the pH of a buffer.
Weak acid + H2O H3O+ + Conjugate base
Ka = [H3O+][conjugate base] [weak acid]
[H3O+] = Ka x [weak acid] [conjugate base]
pH = –log [H3O+]
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Calculation of Buffer pH
The weak acid H2PO4- in a blood buffer H2PO4
-
/HPO42- has Ka = 6.2 x 10-8. What is the pH of the
buffer if it is 0.20 M in both H2PO4- and HPO4
2-?
[H3O+] = Ka x [H2PO4-]
[HPO42-]
[H3O+] = 6.2 x 10-8 x [0.20 M] = 6.2 x 10-8
[0.20 M]pH = –log [6.2 x 10-8] = 7.17
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Learning Check
What is the pH of a H2CO3 buffer that is 0.20 MH2CO3 and 0.10 M HCO3
-? Ka(H2CO3) = 4.3 x 10-7
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Solution
What is the pH of a H2CO3 buffer that is 0.20 MH2CO3 and 0.10 M HCO3
- ?
Ka (H2CO3) = 4.3 x 10-7
[H3O+] = Ka x [H2CO3] [HCO3
-]
[H3O+] = 4.3 x 10-7 x [0.20 M] = 8.6 x 10-7
[0.10 M]
pH = –log [8.6 x 10-7] = 6.07