Ch15. Acids and Bases: A Second Look

1
Ch15. Acids and Bases A Second Look

• Brady Senese, 5th Ed

1
2
Arrhenius acid is a substance that produces H
(H3O) in water
Arrhenius base is a substance that produces OH-
in water
4.3
3
A Brønsted acid is a proton donor A Brønsted base
is a proton acceptor
acid
base
acid
base
conjugate base
conjugate acid
acid
base
15.1
4

(a) Formic acid transfers a proton to a water
molecule. HCHO2 is the acid and H2O is the base.
(b) When a hydronium ion transfers a proton to
the CHO2- ion, H3O is the acid and formate ion
is the base.
5
(No Transcript)
6

• Identify the Conjugate Partner for Each

conjugate base conjugate acid
HCl
NH3
HC2H3O2
CN-
HF
15.1. Brønsted-Lowry acids and bases exchange
protons
6
7
Identify the conjugate pair for each acid/base

• Iodic acid
• Nitrous acid
• Acetic acid
• Bisulfite ion
• Hydrogen sulfate

8
Your Turn!

• How many of the following pairs are conjugate
  pairs
• HCN/CN- ii. HCl/Cl- iii. H2S/S2-
• 1
• 2
• 3
• None of them are conjugate

15.1. Brønsted-Lowry acids and bases exchange
protons
8
9
(No Transcript)
10
(No Transcript)
11
(No Transcript)
12

• An amphoteric substances can act as either an
  acid or base, also called amphiprotic, and can be
  either molecules or ions

13
Your Turn!

• How many of the following are amphoteric?
• HC2H3O2 , H2PO42-, HSO4-
• 1
• 2
• 3
• None of these

15.1. Brønsted-Lowry acids and bases exchange
protons
13
14
(No Transcript)
15
Strong Acid
Weak Acid
15.4
16
ACID-BASE THEORIES

• Acetic acid is only 0.42 ionized when HOAc
  1.0 M. It is a WEAK ACID
• HOAc H2O H3O
  OAc-
• WEAK A base acid STRONG B
• Because H3O is small, this must mean
• 1. H3O is a stronger acid than HOAc
• 2. OAc- is a stronger base than H2O

17
Identify The Preferred Direction Of The Following

• H3O (aq) CO32-(aq) ? HCO-3(aq)
  H2O (l)
• NH4(aq) HCO-3(aq) ? NH3(aq)
  H2CO3(aq)
• Cl- HCN(aq) ? HCl(aq)
  CN-(aq)

H3O
HCN
H2O
H2CO3
NH4
Increasing Acid Strength
15.1. Brønsted-Lowry acids and bases exchange
protons
17
18
15.4
19
Your Turn!

• Which reaction is not written as in the preferred
  direction.
• HC2H3O2 H2AsO4- ?H3AsO4 C2H3O2-
• H3AsO4 H2AsO3- ? H2AsO4- H3AsO3
• HC2H3O2 H2AsO3- ?C2H3O2- H3AsO3
• All are preferred as written

H3O
HC2H3O2
H3AsO3
H2O
H3AsO4
Increasing Acid Strength
15.1. Brønsted-Lowry acids and bases exchange
protons
19
20
Periodic Trends Of Binary Acids (HnX )

• As we read left to right in a period, increasing
  electronegativity of X makes the H-X bond more
  polar
• Acid strength increases with increasing polarity
• As we read top to bottom in a group, the acid
  strength increases due to increasing bond length
  of the HX bond due to increased radius of the
  anion, X

15.2. Strengths of Brønsted acids and bases
follow periodic trends
20
21
Molecular Structure and Acid Strength
H X-
H X
The stronger the bond
The weaker the acid
HF ltlt HCl lt HBr lt HI
15.9
22
Learning Check

• Which is a stronger acid?
• H2S or H2O
• CH4 or NH3
• HF or HI

d-
d-
d
d
d-
d
d
d
d
d-
d-
15.2. Strengths of Brønsted acids and bases
follow periodic trends
22
23
Oxoacids ( A(O)m(OH)n)

• Increase in strength as the electronegativity of
  the central atom, A, increases
• Increase in strength as the number of oxygen
  atoms on (hence the oxidation state of) the
  central atom, A, increases
• Electrical induction through the central atom
  weakens strength of the bond to H

                                                
                                                  
                       
d
d-
d
d-
15.2. Strengths of Brønsted acids and bases
follow periodic trends
23
24
Learning Check

• Which is a stronger acid?
• H2SO4 or H3PO4
• HNO3 or H3PO4
• H2SO4 or H2SO3
• HNO3 or HNO2

15.2. Strengths of Brønsted acids and bases
follow periodic trends
24
25
Anions Of Oxoacids Are Basic

• Oxygen atoms are electron withdrawing, thus the
  charge on an anion is located on the lone oxygens
• The more oxygen atoms there are that share the
  same charge, the less basic is the anion
• The stronger the base behavior of the anion, the
  greater the strength of the conjugate acid

-
-
2 O share the (-) charge
3 O share the (-) charge
15.2. Strengths of Brønsted acids and bases
follow periodic trends
25
26
Your Turn!

• Which statement about acid strength is false
• Binary acids get stronger as the anion gets
  larger
• Ternary oxoacids get stronger as the central atom
  increases in size
• Ternary acid strength increases with increasing
  oxidation state
• None of these are false

15.2. Strengths of Brønsted acids and bases
follow periodic trends
26
27
Rank by Acid Strength

• HI HBr HCl HF
• HClO4 HClO3 HClO2 HClO
• HClO HBrO HIO

28
Lewis Acid/Base Reactions

• Lewis acids accept an electron pair to form
  coordinate covalent bonds
• Lewis bases donate lone pairs of electron to form
  coordinate covalent bonds
• Neutralization is the formation of a coordinate
  covalent bond between the donor and acceptor

15.3. Lewis acids and bases involve coordinate
covalent bonds
28
29
Lewis Acids and Bases
H
H
F
F

F B

F B
N H
N H

H
F
F
H
acid
base
No protons donated or accepted!
15.12
30
(No Transcript)
31

• In general, most metal oxides react with water to
  form bases, and nonmetal oxides react with water
  to form acids
• In Section 5.5 metal oxides were called base
  anhydrides and nonmetal oxides were called acid
  anhydrides
• When cations dissolve in water, they form species
  called hydrated ions
• Hydrated metal ions tend to be Brønsted acids

32

• For the monohydrate of the metal ion Mn the
  equilibrium can be represented as

The metal ion makes the hydrogen on the water
more acidic.
33
(No Transcript)
34

• The charge density of a cation is its charge
  divided by its volume
• The higher the charge density, the better a
  cation is at drawing electron density from a O-H
  bond and the more acidic it is
• Within a given period, the cation size increases,
  and the charge density decreases, from top to
  bottom
• As a result, the most acidic hydrated cations are
  found at the top of a group
• As the cation charge increases, it becomes more
  acidic

35
(No Transcript)
36

• Water undergoes self-ionization or autoionization
  making it a weak electrolyte
• This equilibrium is described by the ion product
  of water

37
The Ion Product of Water
HOH-
Kc
H2O constant
H2O (l) H (aq) OH- (aq)
H2O
KcH2O Kw HOH-
The ion-product constant (Kw) is the product of
the molar concentrations of H and OH- ions at a
particular temperature.
Solution Is
H OH-
neutral
At 250C Kw HOH- 1.0 x 10-14
H gt OH-
acidic
H lt OH-
basic
15.2
38
Learning Check

• Complete the following with the missing data

OH- H3O pH
3.2 10-3 M
2.3 10-5 M
1.5 10-2 M
2.55 10-6 M
8.50
15.5. pH is a measure of the acidity of a
solution
38
39
Learning Check

• Complete the following with the missing data

pH pOH H3O
2.33
1.89
15.5. pH is a measure of the acidity of a
solution
39
40
What is the H3O in a HCl solution that has a
concentration of 5.9E-2M? a) 5.9E-2 M b)
3.0 E-2 Mc) 1.0 E-2 M d) 1.2 E-1 M e) 1.23
M
At 250C Kw HOH- 1.0 x 10-14
41

• What is the pH of a solution that has a OH-
  1.210-3 M?
• 2.92
• 11.1
• 1.20
• None of the above

15.5. pH is a measure of the acidity of a
solution
41
42
What is OH- in a Ba(OH)2 solution that has a
concentration of 3.3E-2M? a) 1.7 E-2 M b) 3.3
E-2 M c) 6.6 E-2 M d) 1.2 E-1 Me) 0.23 M
At 250C Kw HOH- 1.0 x 10-14
43

44
(No Transcript)
45
Indicators Help Us Estimate pH
15.5. pH is a measure of the acidity of a
solution
45
46
pFUNCTIONS

• pX - log X
• pH - log H
• pOH - log OH-
• pK -log K

47
The pH of rainwater collected in a certain region
of the northeastern United States on a particular
day was 4.82. What is the H ion concentration
of the rainwater?
pH -log H
15.3
48
The OH- ion concentration of a blood sample is
2.5 x 10-7 M. What is the pH of the blood?
15.3
49
Strong Acids Ionize 100 in Water

• As the substances are placed into water, they
  form H3O .
• The H3O formed by the acid suppresses waters
  ionization. (if acid gt 10-7 M)
• The pH can be calculated from the concentration
  of H3O produced by the strong acid
• The reaction of strong acids occurs irreversibly,
  so we show the reaction with a ? instead of using
  a double arrow

15.6. Strong acids and bases are fully
dissociated in solution
49
50
Learning Check

• What is the pH of 0.1M HCl

15.6. Strong acids and bases are fully
dissociated in solution
50
51
Learning Check

• What is the pH of 0.1M HCl

• HCl(aq) H2O(l) ?H3O(aq) Cl-(aq)
• 0.1 N/A 0 0 I
• -0.1 -0.1 0.1 0.1 C
• 0 N/A 0.1 0.1 end
• pH -log(0.1) 1

15.6. Strong acids and bases are fully
dissociated in solution
51
52
Strong Bases Dissociate 100 In Water

• They are strong electrolytes that form OH- when
  dissolved
• pOH can be calculated from the OH- from the
  solution
• Waters contribution is negligible if the base is
  sufficiently concentrated OH-gt10-7M

15.6. Strong acids and bases are fully
dissociated in solution
52
53

• What is the pH of 0.5M Ca(OH)2?

15.6. Strong acids and bases are fully
dissociated in solution
53
54

• What is the pH of 0.5M Ca(OH)2?

Ca(OH)2(aq) ? Ca2(aq) 2OH-(aq) 0.5 0 0
I -0.5 0.5 0.52 C 0 0.5 1.0
E pOH -log(1.0) 0 pH 14
15.6. Strong acids and bases are fully
dissociated in solution
54
55
Your Turn!

• What is the pH of a 0.50M solution of NaOH?
• 0.500
• 0.301
• 13.7
• None of these

15.6. Strong acids and bases are fully
dissociated in solution
55
56
What is the pH of an NaOH solution that has a
concentration of 3.3E-3 M? a) -2.48b) 2.48c)
11.52d) 1.2 E1,e) 12.52,
57
What is the final pH, if 200 mL of 3.3E-2 M HNO3
is diluted with water to a final volume of 328
mL? a) -1.27 b) 2.0E-2 c) 5.4E-2d) 1.27 e)
1.69
58
What is the pH of a 3.3E-2 M Ba(OH)2
solution? a) -1.48 b) -1.18 c) 1.18 d) 12.52
e) 12.82
59
In a pure aqueous solution of NaOH, the pH was
measured to be 13.41. What is the molar
concentration of NaOH? a) 3.9E-14 Mb) 5.7E-1
Mc) 0.26 M d) 0.48 Me) 2.6E13 M
60
What is the final molarity of H3O, if 100 mL
of 7.0E-2 M HCl is diluted with 236 mL of
distilled water? a) 3.0E-4 M b) 2.1E-2 Mc)
3.0E-2 M d) 1.7E-1 M e) 2.4E-1 M
61
Exactly 100 mL of 0.20 M NaOH was mixed with 125
mL of 0.20 M HCl. What is the molarity of the
NaCl formed? a) 1.6E-1 Mb) 1.8E-1 Mc) 1.8E-2
Md) 8.9E-2 Me) 0.20 M
62
Exactly 100 mL of 0.20 M NaOH was mixed with 125
mL of 0.20 M HCl. What is the pH of this mixture
? a) 0.70b) 0.80c) 1.65d) 1.80e) 7.80
63
Exactly 100 mL of 0.20 M NaOH was mixed with 118
mL of 0.30 M HCl.What is the pH of this mixture?
a) 0.80b) 1.15c) 2.13 d) 3.12e) 12.45
64
(No Transcript)
65
(No Transcript)
66
(No Transcript)
67
(No Transcript)
68
(No Transcript)