This chapter is about acid and base.

1. AcidsAcids andand BasesBases
17 Acid and Base 1
A group of chemical properties is related to acidity. According to these
properties, a substance can be called an acid or a base.
The word acid comes from Latin acere meaning sour. A base is an
alkaline, which is derived from Arabic alqali.
Presence of acids and bases have been recognized by ancient people.
Lavoisier named oxygen as the element from which acids are derived.
Liebig (German) proposed that an acid contains hydrogen.
Many chemical reactions are called acid-base reactions; they are not
necessarily neutralizations.
The acid-base concept is interesting, especially the way it evolved.
Understand acid or base, important properties of substances.

2. Answer these questions
17 Acid and Base 2
What are acids?
What are bases?
What are acid-base reactions?
What are neutralization reactions?
What are the relationships between acids and bases?
What is the role of the solvent in acid or base solutions?
How does the acid-base concept evolve and why?
What are Arrhenius acid, Bronsted-Lowry acid and Lewis acids?
What is the relationship between conjugate acids and bases?
What does pH mean and how is the pH scale related to acidity?
What are salts?
Understand important properties of substances

3. Arrhenius acids and bases
17 Acid and Base 3
The fundamental concept: (Text PHH: 17-1)
Acid - any substance which delivers hydrogen ion (H+
) to the solution.
HA → H+
+ A¯
Base - any substance which delivers hydroxide ion (OH¯) to the
solution. BOH → X+
+ OH¯
Sevante Arrhenius proposed that substances exists as ions in solution in
his dissertation, which was awarded a fourth class (D) in 1884. He was
unable to find a job in his native Sweden.
He was awarded the Nobel Prize in 1903 for his electrolytic
dissociation theory.

4. Problems with Arrhenius
theory
17 Acid and Base 4
Like Dalton’s atomic theory, Arrhenius theory have problems today:
Acidity did not show in other solvent. What is the solvent role?
Some salts produce acidic or basic solutions, not neutral. Why?
Which is the base, NH3 or NH4OH? Is OH¯ really the only base?
How can H+
be stable? Are proton donated?
Some chemists want students to learn Brønsted-Lowry theory of acids and
bases before learning Arrhenius theory, because the former is more general.
Question the established theory.

5. Brønsted-Lowry theory of acids and bases
17 Acid and Base 5
An acid is a substance from which a proton can be removed.
Acids are proton donors.
A base is a substance that can remove a proton from an acid.
Bases are proton acceptors.
Because of strong desire for protons, bases rip protons off acids.
Acid-base reactions are competitions for protons.
HCl + H2
O ↔ H3
O+
+ Cl¯
HNO3
+ H2
O ↔ H3
O+
+ NO3
¯
HC2
H3
O2
+ H2
O ↔ H3
O+
+ C2
H3
O2
¯
H2
O + NH3
↔ NH4
+
+ OH¯
conjugate acids and bases
17–2

6. Problems with B-L theory
17 Acid and Base 6
The theory works very nicely in all protic solvent, but fails to
explain acid-base behavior in aprotic solvents and non-solvent
situations.
A more general concept on acid and base was proposed by G.N.
Lewis at about the same time Bronsted-Lowry theory was proposed.
Question the established theory.

7. Evolution of the acid-base
concept
17 Acid and Base 7
year thinker Acid Base acid-base reaction
1884 Arrhenius ionize ionize H+
+ OH¯ = HOH
H+
OH¯
1923 Bronsted- Proton proton HA + B = HB + A
Lowry Donor acceptor conjugation
1923 Lewis electrophil nucleophil E + Nu = E:Nu

8. Lewis acids and bases
17 Acid and Base 8
Gilbert Newton Lewis (1875-1946) influential
American chemist. His theories include the Lewis
dot structure taught in Chem120 and covalent bond
theories.
Lewis acids are electrophils: H+
, Na+
, BF3,
Lewis bases are nucleophils: NH3, H2O, PH3
Acid base reactions:
BF3 + :NH3 → F3B:NH3
Lewis at his desk.
He generalized an idea.
17–9

9. Relative strengths of
acids and bases
17 Acid and Base 9
HClO4 ClO4 ¯
H2SO4 HSO4¯
HI I¯
HBr Br¯
HCl Cl¯
HNO3 NO3¯
H3O+ H2O
HSO4¯ SO4
2
¯
H2SO3 HSO3 ¯
H3PO4 H2PO4 ¯ HNO2
NO2¯
HF F ¯
HC2H3O2 C2H3O2 ¯
Al(H2O)6
3+
Al(OH)(H2O)5
2+
H2CO3 HCO3 ¯
H2S HS ¯
HClO ClO¯
HBrO BrO¯
NH4
+
NH3
HCN CN ¯
HCO3¯ CO3
2
¯
H2O2 HO2
HS ¯ S2
¯
H2O OH¯
ROH RO¯
17–4 & 17–5 Table 17–3
The stronger the acid, the weaker
its conjugate base.

10. Skills regarding strength of
acids
17 Acid and Base 10
What are strong acids?
What are strong bases?
Which is the strongest acid, HF, HCl, HBr, or HI?
How about HNO3 and HNO2? H2SO4, H2SO3?
How about HClO4, HClO3, HClO2, HClO, and HCl?
What is the strongest acid in an aqueous solution?
What is leveling effect?
Order a given list according to the strength.
Interpret reactions as due to strength of acids and bases.
Explain strength with related acids and bases.

11. Molecular structure and acid
strength
17 Acid and Base 11
A strong acid loses its proton easily. A strong base holds onto a proton
tightly.
The more polarized is the
H—X
bond in an acid, the easier the molecule releases H+
thus a stronger
acid.
The weaker the H —X bond, the easier the molecule releases H+
thus a
stronger acid.
The bond strength and the polarity are related to electronegativity and
electrostatic interactions – size of the ions.
17–8
Able to predict acidity from molecular structure.

12. Self-ionization of water
17 Acid and Base 12
Water molecules autoionize
2 H2O (l) = H3O+
(aq) + OH¯ (aq)
[H3O+
] [OH¯]
Kc = ————————
[H2O] (= 1000/18 = 55.6)
Kw = [H2O] Kc = 1e–14 only at 25o
C, it’s T dependent.
The ion product, Kw increases as T increases, and its value remains the
same in the presence of acid or base.
17 – 3
The molecule of life, H2O, and its acidity.

13. Solutions of strong acids and bases
17 Acid and Base 13
Strong acids and strong bases completely ionize in their solutions.
HCl (aq) + H2O (l) → H3O+
(aq)+ Cl–
(aq)
KOH (aq) → K+
(aq)+ OH–
(aq)
In a 0.100 M HCl or HNO3 solution,
[H+
] = 0.100 M
and [OH–
] = 1e–14 / 0.100 = 1e–13 M at 25o
C
In a 0.100 M NaOH or KOH solution,
[OH–
] = 0.100 M
and [H+
] = 1e–14 / 0.100 = 1e–13 M at 25o
C
In a 0.010 M Ca(OH)2 solution,
[OH–
] = 2*0.010 = 0.020 M
[H+
] = 1e–14 / 0.020 = 5e–13 M at 25o
C

14. Some strong acids and bases
17 Acid and Base 14
Strong acids
Hydrogen halides
HCl HBr HI
Oxyacids of halogens
HClO3 HBrO3 HIO3
HClO4 HBrO4 HIO4
Other oxyacids
H2SO4 HNO3
Strong Bases
Hydroxides of alkali metals
NaOH KOH CsOH
Hydroxides of alkali earth
Ca(OH)2 Sr(OH)2
17 – 4

15. Neutralization Reactions
17 Acid and Base 15
The neutralization reaction between strong acids and strong bases has the
net ionic reaction
H3O+
(aq)+ OH–
(aq) = 2 H2O
The anions are bystander ions. They do not participate the reaction. These
ions are
I–
, Br–
, Cl–
, NO3
–
, HSO4
–
, CClO4
–
, Na+
, K+
, Cs+
, Ca2+
etc.
When dried, the ions left behind in neutralization reactions form salts.

16. The pH scale
17 Acid and Base 16
Sorensen introduced the pH scale in 1909 using the symbol pH
.
The p is from the German word potenz, power of (10).
pH = – log [H+
]; [H+
] = 10 –pH
pOH = – log [OH–
]; [OH–
] = 10 –pOH
pK = – log [K]; K = 10 –pK
pH = 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
[H+
] = 0.79 0.63 0.50 0.40 0.32 0.25 0.20 0.16 0.13
(not linear; need not copy, figure out yourself)
For aqueous solution;
Kw = [H+
] [OH–
]
- log Kw = pH + pOH = 14 only at 25o
C
17–3, p–672

17. pH meter and pH electrodes
17 Acid and Base 17
The pH meter is based on the principle to be
discussed in electrochemistry.
This topic is also related to the equilibrium
constant K and Gibbs free energy, ∆G.

18. Neutrality
17 Acid and Base 18
In a neutral solution, [H+
] = [OH–
]. (Different from Fig. 17-5)
In an acidic solution, [H+
] > [OH–
], and a basic solution, [H+
] < [OH–
].
In a saturated CaO (same as Ca(OH)2) solution, [OH–
] = 0.025.
Calculate pH, [H+
], [Ca2+
], and pOH at 25o
C.
Solution:
pOH = – log 0.025 = 1.60
pH = 14.00 – 1.60 = 12.40 only applicable at 25o
C
[H+
] = 10–12.40
= 4.0e–13 M Note that 4.0e-13*0.025 = 1e-14
[Ca2+
] = [OH–]
/ 2= 0.013 M

19. Answer these questions –
review
17 Acid and Base 19
What are acid-base reactions?
What are neutralization reactions?
What is the role of the solvent in acidity?
What does pH mean and how is the pH scale
related to acidity?
What are salts?

20. Acid-Base Equilibria
17 Acid and Base 20
Strong acids and bases completely ionize in their aqueous solutions.
HCl → H+
+ Cl–
KOH → K+
+ OH–
Weak acids and bases ionize but not completely in their solutions.
HCH3COO ↔ H+
+ CH3
COO–
acetic acid, vinegar spirit
HNic ↔ H+
+ Nic–
HNic = Niacine, C5NH5COOH, a water-soluble vitamin required by the
body for health, growth and reproduction; part of the vitamin B
complex. It was first prepared in pure form by oxidizing nicotine
using conc. HNO3. Nicotine is a major chemical in tobacco .
N N
CH3
N
COOH
<= Nicotine
Niacine =>
Vitamine
B3

21. Caffeine
17 Acid and Base 21
Caffeine C8H10N4O2 is a weak base,
(pH of 1% soln 6.9) taste bitter
smell like tea, a cardiac stimulant,
(boost of energy), mild diuretic,
addictive, operates using the same
mechanisms that amphetamines,
cocaine and heroin use to
stimulate the brain.
Crystals are hexagonal prisms by
sublimation, mp 238°C. Sublimes
178°. Fast sublimation is obtained
at 160-165° under
1 mm Hg pressure.
Many organic bases are interesting
drugs, and their chemistry is
fascinating.

22. Ionization of weak acids
17 Acid and Base 22
Ionization of acetic acid, HCH3COO, HA
HA = H+
+ A–
same as HA + H2O = H3O+
+ A–
[H+
] [A–
] A–
= CH3COO–
(acetate)
Ka = ————— Ka acid ionization constant, important for an acid
[HA] Ka equilibrium constant with solvent effect
The pKa is defined similar to the pH,
pKa = – log Ka Ka = 10 –pKa
See Table 17-3 on page 678

23. Some weak acids and bases
17 Acid and Base 23
Common Weak Acids
Formic acid HCOOH
Acetic acid CH3COOH
Trichloroacetic acid CCl3COOH
Hydrofluoric HF
Hydrocyanic HCN
Hydrogen sulfide H2
S
Water H2
O
Conjugate acids
of weak bases NH4
+
Common Weak Bases
ammonia NH3
trimethyl ammonia N(CH3
)3
pyridine C5
H5
N
ammonium hydroxide NH4
OH
water H2
O
HS-
ion HS-
conjugate bases of
weak acids e.g.: HCOO-

24. Determine Ka and percent ionization
17 Acid and Base 24
Nicotinic acid, HNic, is a monoprotic acid. A solution containing 0.012 M
HNic, has a pH of 3.39. What is its Ka? What is the percent of ionization?
Solution:
HNic = H+
+ Nic–
0.012-x x x
x = [H+
] = 10–3.39
= 4.1e-4
[HNic] = 0.012 – 0.00041 = 0.012
(4.1e-4)2
Ka = ————— = 1.4e-5
0.012
Degree of ionization = 0.00041 / 0.012 = 0.034 = 3.4%

25. Application of Ka
17 Acid and Base 25
The Ka of nicotinic acid, HNic, is 1.4e-5. A solution containing 0.22 M
HNic. What is its pH? What is the degree of ionization?
Solution:
HNic = H+
+ Nic–
0.22-x x x
x 2
Ka = ———— = 1.4e-5
0.22 – x (use approximation, small indeed)
x = √ (0.22*1.4e-5) = 0.0018 pH = – log (0.0018) = 2.76
Degree of ionization = 0.0018 / 0.22 = 0.0079 = 0.79%
compare with 3.4% when the solution was 0.012 M

26. pH of a weak acid
17 Acid and Base 26
The pH of C M acid HA (Ka) solution.
Method:
HA = H+
+ A–
C-x x x
x 2
Ka = ————
C – x
x 2
+ Ka x – C Ka = 0
– Ka + √Ka
2
+ 4 C Ka
x = ———————————
2
pH = – log x
The pOH of C M base BOH
(Kb) solution.
Method:
BOH = B+
+ OH–
C-y y y
y 2
Kb = ————
C – y
y 2
+ Kb x – C Kb = 0
– Kb + √Kb
2
+ 4 C Kb
y = ———————————
2
pOH = -log y

27. Using the quadratic formula
17 Acid and Base 27
The Ka of nicotinic acid, HNic, is 1.4e-5. A solution containing 0.00100 M
HNic. What is its pH? What is the degree of ionization?
Solution:
HNic = H+
+ Nic–
0.001-x x x
x2
Ka = —————— = 1.4e-5 x2
+ 1.4e-5 x – 1.4e-8 = 0
0.00100 – x
–1.4e–5 + √ (1.4e–5)2
+ 4*1.4e-8
x = —————————————————— = 0.000111 M 2
pH = – log (0.000111) = 3.95
Degree of ionization = 0.000111/ 0.001 = 0.111 = 11.1%
Deg.’f ioniz’n
0.22 0.79%
0.012 3.4 %
0.001 11.1 %
x 2
+ Ka x – C Ka = 0
– Ka + √Ka
2
+ 4 C
Ka
x = ———————————
2

28. Degree of or percent ionization
17 Acid and Base 28
Deg.’f ioniz’n
0.22 0.79%
0.012 3.4 %
0.001 11.1 %
The degree or percent of ionization of a weak
acid always decreases as its concentration
increases, as shown from the table given
earlier.
Concentration of acid
% ionization

29. Polyprotic acids
17 Acid and Base 29
Polyprotic acids such as sulfuric and carbonic acids have more than one
hydrogen to donate.
H2SO4 = H+
+ HSO4
–
Ka1 very large completely ionized
HSO4
–
= H+
+ SO4
2–
Ka2 = 0.012
H2CO3 = H+
+ HCO3
–
Ka1 = 4.3e-7
HCO3
–
= H+
+ CO3
2–
Ka2 = 4.8e-11
Ascorbic acid (vitamin C)
is a diprotic acid, abundant
in citrus fruit.
Others:
H2S, H2SO3, H3PO4, H2C2O4 (oxalic acid) …
C

30. Aspartame -
nutrasweet
17 Acid and Base 30
A dipeptide methyl ester :
L-aspartyl-L-phenylalanine methyl ester
C14H18N2O5 (molar mass = 294.31)
Aspartame has two ionizable protons
1965. Jim Schlatter
synthesized it and
discovered it sweet

31. Species concentrations of diprotic acids
17 Acid and Base 31
Evaluate concentrations of species in a 0.10 M H2SO4 solution.
Solution:
H2SO4 = H+
+ HSO4
–
completely ionized
(0.1–0.1) 0.10+y 0.10-y
HSO4
–
= H+
+ SO4
2–
Ka2 = 0.012
0.10–y 0.10+yy Assume y = [SO4
2–
]
(0.10+y) y
————— = 0.012
(0.10-y)
[SO4
2–
] = y = 0.01M
[H+] = 0.10 + 0.01 = 0.11 M;
[HSO4
–
] = 0.10-0.01 = 0.09 M
Y2
+ 0.112 y – 0.0012 = 0
- 0.112+√0.1122
+ + 4*0.0012
y = —————————————— = 0.0098
2
If concentration’f H2SO4 = 1.0 M,
what doUdo?

32. Species concentrations of weak diprotic acids
17 Acid and Base 32
Evaluate concentrations of species in a 0.10 M H2S solution.
Solution:
H2S = H+
+ HS–
Ka1 = 1.02e-7
(0.10–x) x+y x-y Assume x = [HS–
]
HS–
= H+
+ S2–
Ka2 = 1.0e-13
x–y x+y y Assume y = [S2–
]
(x+y) (x-y) (x+y) y
————— = 1.02e-7 ———— = 1.0e-13
(0.10-x) (x-y)
[H2S] = 0.10 – x = 0.10 M
[HS–
] = [H+
] = x ± y = 1.0e–4 M;
[S2–
] = y = 1.0e-13 M
0.1>> x >> y:
x+ y = x-y = x
x = √0.1*1.02e-7 =
1.00e-4
y = 1e-13
See Example 16.4

33. Beware of Misconceptions
17 Acid and Base 33
These equations show dynamic equilibria at the molecular level in a
system. These equations are not separate reactions, but they indicate
possible combination and dissociation in both directions.
H2S = H+
+ HS–
Ka1 = 1.02e-7
HS–
= H+
+ S2–
Ka2 = 1.0e-13
H2O = H+
+ OH-
Kw = 1e-14
H2O
H2O
H2S
HS-
H+
H+
H+
H2S
H2O
H2O H2S
OH-
OH-
OH-
S2-
OH-
S2-
S2-
H+
H2S(g)
HS-

34. Base-ionization constant
17 Acid and Base 34
For acid, HA
HA = H+
+ A–
[H+
] [A–
]
Ka = —————
[HA]
The pKa is defined similar to the pH,
pKa = – log Ka Ka = 10 –pKa
From slide 3
For a base BOH,
BOH = B+
+ OH–
[B+
] [OH–
]
Kb = ———————
[BOH]
The pKb is defined similar to pKa
pKb = – log Kb, Kb = 10–pKb
Whatever you have learned for weak
acids apply to weak bases
June 18

35. Common weak bases
17 Acid and Base 35
Substance Formula Kb
Ammonia NH3 1.8e-5
aniline C6H5NH2 4.2e-10
dimethylamine (CH3)2NH 5.1e-4
ethylamine C2H5NH2 4.7e-4
Hydrozine N2H4 1.7e-6
Hydroxylamine H2NOH 1.1e-8
methylamine CH3NH2 4.4e-4
Pyridine C5H5N 1.4e-9
Urea NH2CONH2 1.5e-14
no need to copy Table 16.2
Many drugs are salts of
weak bases, such as
Advil
Pseudoephedrine HCl
Buckley's mixture
Dextromethorphan
hydrobromide
Dristan
Traxodone HCl

36. Made by Sahil Raj…
17 Acid and Base 36