ACIDS AND BASES

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CHAPTER 14 ACIDS AND BASES
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Acid Definitions 1) Arrhenius substance that
produces H(aq) or H3O(aq) in
solution
HNO3(aq) H2O(l) ltgt H3O(aq) NO31-(aq)
2) Bronsted- Lowry proton ( H ) donor
NH3(g) HCl(g) gt NH4Cl1-(s)
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3) Lewis electron - pair acceptor
Ag1(aq) 2 NH3 ltgt Ag(NH3)2 1
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Conjugate acid what is formed when a base
gains a proton
Conjugate base what is formed when an
acid donates a proton
HNO2(aq) H2O(l) ltgt H3O(aq)
NO2-(aq)
acid base
Conj. Acid conj. base
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HNO3(aq) gt H(aq) NO31-(aq)
Ka acid dissociation constant equilibrium
constant
Ka H NO3 gt 1 HNO3
STRONG ACIDS
HClO4 HBr HI HCl HNO3 H2SO4
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The stronger an acid, the weaker its conjugate
base.
An acid will transfer a proton to any base that
is stronger than its conjugate base.
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STRONG ACID WEAK BASE
HClO4 ClO41-
HNO3 NO31- H3O H2O H2CO3
HCO31- HC2H3O2 C2H3O21- H2S
HS1- NH4 NH3 HCO31-
CO32- H2O OH1- NH3 NH21-
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HClO4 HS1- ltgt
H2S ClO41-
NO31- H2S ltgt
N. R.
NH3 ClO41- explosive
HClO4 NH21- ltgt
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Amphoteric
Substance which acts as an acid or a base
depending on substance reacting with it)
H2O(l) H2O(l) ltgt
H3O(aq) OH1-(aq)
Kw H3O OH1- 1.0 x 10-14 at 25oC
Kw ionization constant for water
pH - log H3O
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M H3O OH- pH
pOH
NaOH .030
3.3 x 10-13
.030
12.48
1.52
HNO3
.042
2.4x10-13
4.2 x 10-2
1.38
12.62
H2SO4 .0001
3.7
5x10-11
10.3
.0002
HCl 5.631
2.34x10-6
4.28x10-9
8.369
2.34x10-6
Ca(OH)2 .060
.030
1.7x10-13
12.78
1.22
KOH
2.61x10-4
3.83x10-11
2.61x10-4
3.583
10.417
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WEAK ACID SOLUTIONS
same old, same old equilibrium calculations
Calculate the pH and dissociation of a
.500-M solution of formic acid, HCOOH. Ka 1.77
x 10-4
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0.500 0 0
HCOOH(aq) ltgt H(aq) COOH1-(aq)
.500 - x x x
1.77 x 10-4 COOH1- H HCOOH
x2 / ( .500 - x ) x2 / .500
X H3O 9.41 x 10-3
pH 2.03
(9.41 x 10-3 / .500) x 100
1.88
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Calculate the pH of a 0.200 M solution
of citric acid, C6H10O8 HA Ka 7.45 x 10-4
.200 0 0
HA ltgt H A1-
.200 - x x x
7.54 x 10-4 x2 / (.200 - x )
X2 7.45 x 10-4 x - 1.49 x 10-4 0
X H3O .0118 pH 1.928
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A 0.500 M solution of HA is 1.6
ionized. Find Ka.
.500 0 0
HA ltgt H A1-
Remember ___x____ (100) ionized
original Solve
for x to get equil
x ((ionized)(original ))/100 .016 x .500
.008 M
.5-.008 .00800 .00800
Ka H A1- .008 .008 HA
.500 - .00800
1.3 x 10-4
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Bases

• Strong bases Group I and II hydroxides
• Weak bases NH3, ammonia, and other nitrogen
  containing compounds where nitrogen has a
  non-bonding pair of electrons

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Calculate the pH of a 0.350 M solution
of methylamine, CH3NH2. Kb 4.38 x 10-4
.350 0 0
CH3NH2 H2O ltgt CH3NH3 OH1-
.350 - x x x x OH- formed
Kb CH3NH3 OH-/ CH3NH2 x2/(.350-x)
X OH- .0124 pH 12.093
x2 / .350
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POLYPROTIC ACIDS
Calculate the pH and equilibrium
concentrations of all species of a 1.40 M
solution of oxalic acid, H2C2O4. Ka1 .065
Ka2 6.1 x 10-5
1.40 0 0
H2C2O4 H2O ltgt H3O HC2O41-
1.40 - x x x
.065 H3O HC2O4-1 / H2C2O4
X2 .065x - .091 0
x2 / ( 1.4 - x )
X HC2O41- 0.27
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.27 .27 0
HC2O41- H2O ltgt H3O C2O42-
.27 - y .27 y y
Ka2 6.1 x 10-5 (.27y)(y) .27 -
y
.27y .27
y C2O42- 6.1 x 10-5
H2C 2O4 1.40 - x 1.40 - .27 1.1
H3O .27 y .27 6.1 x 10-5 .27 pH
.57
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Calculate the pH and concentration of 6.0
M H3PO4. Ka1 7.5 x 10-3 Ka2 6.2 x 10-8
Ka3 4.8 x 10-13
x M of react. acid
6.0 0 0
H3PO4 ltgt H H2PO41-
6.0 - x x x
Ka1 .0075 x2 / (6.0 - x ) x2 / 6.0
x H H2PO41- .212
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.212 .212 0
Y M of H2PO41-
H2PO41- ltgt H HPO42-
Ka2 6.2 x 10-8 ( .212 y ) y .212
- y
.212 y .212
y 6.2 x 10-8 HPO42-
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6.2 x 10-8 .212 0 z
M of HPO42- dec.
HPO42- ltgt H PO43-
6.2 x 10-8 - z .212 z z
Ka3 4.8 x 10-13 ( .212 z ) z .212
z 6.2 x 10-8 - z 6.2 x 10-8
z PO43- 1.4 x 10-19
H3PO4 6.0 - .212 5.8 - M pH 0.67
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Find the pH of a .0030 M H2SO4 solution. KHSO4
0.012
.0030 0 0
H2SO4 gt H HSO41-
0 .0030 .0030
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.0030 .0030 0
HSO41- ltgt H SO42- x M of
HSO41- dec.
.0030 - x .0030 x x
.012 (.0030 x ) x .0030 - x
.012 ( .0030 - x ) .0030 x x2
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.012 ( .0030 - x ) .0030 x x2
X2 0.0150 x - 3.6 x 10-5 0
X .0021
H .0030 .0021 .0051
pH 2.29
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ACID - PROPERTIES OF SALTS
Salts ionic compounds, with ions in solution
if soluble
Strong acids/bases have very weak
conjugates no hydrolysis takes place
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HNO2 ltgt H NO21-
Ka H NO21- 4.0 x 10-4
HNO2
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NaNO2 in placed in water. What will happen?
Na is neutral therefore NO2- will be the only
thing that reacts.
NO21- H2O ltgt HNO2 OH1-
Kb HNO2 OH1- NO21-
Ka H NO21- HNO2
X
Kb Ka OH- H Kb Ka Kw 1 x 10 -14
Kb Kw / Ka 10-14 / 4.0 x 10-4 2.5 x
10-11
- Basic anion salt of the weak acid strong base
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NH3 H2O ltgt NH4 OH1-
Kb 1.8 x 10-5 NH4 OH1-
NH3
NH4 H2O ltgt NH3 H3O
Ka NH3 H3O NH4
Kw / Kb
Ka 5.56 x 10-10
Acidic cation salt of weak base and
strong acid
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Find the pH of a 0.500 M solution of NaNO2. Ka
(HNO2) 4.0 x 10-4
.50 0 0
NO21- H2O ltgt HNO2 OH1-
.50 - x x x
Kb Kw/Ka 2.5 x 10-11 x2 / (.50 - x) x2/.50
x OH1- 3.5 x 10-6 pH 8.58
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Find the pH of a 0.800 M solution of NH4CN1-.
Kb 1.8 x 10-5 Ka 6.2 x 10-10
CN1- is a much stronger conjugate base than NH4
acts as a conjugate acid.
See table in book p.693
.800 0 0 CN1- H2O ltgt HCN OH1-
Kb 10-14 / 6.2 x 10-10 1.61 x 10-5 x2
/ (.800 - x) x2 / .800
x OH1- 3.6 x 10-3 pH 11.56
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STRUCTURE AND ACID/BASE PROPERTIES
The greater the bond strength of an O-H bond, the
weaker the acid.
A compound containing the H-O-X group will
produce an ACIDIC solution in water if the O-X
group is strong and COVALENT (Ex. SO3, CO2,NO2).
IF the O-X bond is IONIC, the compound will
produce a BASIC solution in water (Ex. CaO, K2O)