Acids
E5 Lewis Acids and Bases
Bronsted: Acids are proton donors and generate
hydronium ions in aqueous solution.
Session one
Pre-lab (p.141) due at start of lab.
First hour: Discussion of E4
Lab: Parts 1and 2A
Session two
Lab: Parts 2B, 3 and 4
Acids
Problem
• Cations other than H+ are acids that generate
hydronium ions in aqueous solution!
DEMO
Lewis Definition of Acids and Bases
 Cations other than H+ generate hydronium
ions in aqueous solution!
Define acid/base without using the word proton:
Demo example: Al3+ in aqueous solution = ≈ pH 3!
Cl-H +
Acid
•
•
O
••
H
H
Cl-
H
Base
Base
H
••O
+
H
Acid
 A BASE DONATES unbonded ELECTRON PAIR/S.
 An ACID ACCEPTS ELECTRON PAIR/S .
Deodorants and acid loving plant foods contain aluminum salts
1
Lewis Bases
Lewis Acids
Electron rich species; electron pair donors.
 Electron deficient species ; potential electron
pair acceptors.
H+
Examples:
Cu2+
Al3+
“I’m deficient!”
Ammonia
(ammine)
hydroxide ion
(hydroxo)
water__
(aquo)
Acid
Lewis Acid-Base Reactions
Lewis Acid-Base Reactions
 Metal ions react with/bond to water molecules to
Example
H+ +
Acid
•
•O
• •
+
H
H
Base
H
H
••O
+
H
form aquo complex ions in aqueous solution.
• Example: [Na(H2O)6]+
Complex ion
 The acid reacts with the base by bonding to one or
more available electron pairs on the base.
 The acid-base bond is a coordinate covalent bond.
 The product is a complex or complex ion
2
Aquo Complex Ions
 When a salt dissolves, the metal ions in solution react
with/bond to water molecules to forms aquo complex ions.
Example:
CuSO4 (s) → Cu2+(aq) + SO42- (aq)
Aquo Complex Ions
Examples
[H(H2O)]+
[Cu(H2O)4]2+
Hydronium ion
Tetra aquo copper(II)ion
[Cu(H2O)4]2+
[Pb(H2O)4]2+
[Ni(H2O)6]2+
Tetra aquo lead ion
Hexa aquo nickel ion
 Colored aquo complex ions contain a transition
metal ion with incompletely filled d orbitals.
Part 1. Acidity of Cations
• Study the reaction of metal aquo complex ions with
the Lewis base H2O to produce hydronium ions.
Collect pH data for different metal aquo complex
ions in aqueous solution.
• pH versus periodic table position of ion’s metal?
• pH versus metal ion size and charge? extent of s’
Metal Ion Acid Strength
M
x+ ..
.. O
H∝ +
H∝+
 The acid strength of a metal ion is dependent on its
ability to attract electrons (oxidizing agent strength)
 The water molecules bonded to metal ions in aquo
complex ions are polarized and the protons are
electron deficient.
 The greater the acid strength of a metal ion the more
polarized the bonded water molecules in the aquo
complex ion.
3
Reactions of Metal Aquo Complex Ions with Water
Q. Complete a balanced equation to show formation of
hydronium ions:
Reaction of Metal Aquo Complex Ion:
[Al (H2O)6]3+ + H2O → [Al(H2O)5(OH)]2+ + [H-H2O]+
 Electron deficient proton/s in the polarized water
molecules of the metal aquo complex ion react and
bond to an electron pair in another water molecule
[Al(H2O)6]3+ + 2 HOH → [Al(H2O)4(OH)2]+ + 2 [H3O]+
 When a proton bonds to a water molecule, a H3O+
ion is formed.
Metal Ion Acid Strength
1A
1
Q. Given the reducing agent strength Na > Mg > Al,
indicate the Lewis acid strength of Na+, Mg2+, and Al3+
Al3+ > Mg2+ > Na+
Metal Ion Acid Strength: ___________________
1s1
He
Acid strength: Al3+ > Mg 2+ > Na +
3
2s1
11
2s2
12
3s1
19
3s2
20
4s1
37
10 1 10 2
4s2 3d1 4s2 3d2 4s2 3d3 4s2 3d5 4s1 3d5 4s2 3d6 4s2 3d7 4s2 3d8 4s2 3d 4s 3d 4s 4s2 4p14s2 4p2 4s2 4p3 4s2 4p4 4s2 4p5 4s2 4p6
38 39 40 41 42 43 44 45 46 47 48
49 50
51 52
53 54
5s1
55
5s2 4d1 5s2 4d2 5s2 4d3 5s2 4d5 5s1 4d5 5s2 4d7 5s1 4d8 5s1 4d10 4d 5s 4d 5s 5s2 5p1 5s2 5p2 5s2 5p3 5s2 5p4 5s2 5p5 5s2 5p6
56 57 72 73 74 75 76 77 78 79 80
81 82
83 84
85 86
Ba La* Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
10 1 10 2
6s2 5d1 6s2 5d2 6s2 5d3 6s2 5d4 6s2 5d5 6s2 5d6 6s2 5d7 6s2 5d9 6s1 5d 6s 5d 6s 6s2 6p1 6s2 6p2 6s2 6p3 6s2 6p4 6s2 6p5 6s2 6p6
Li
Na
Be
6s1
87
Fr
7s1
B
Ca
13
Al
IIIB
IVB VB
VIB VIIB VIIIB ⇔ VIIIB
IB
21
22
24
29
Sc
Y
Ti
Zr
23
V
Cr
25
26
Mn Fe
Nb Mo Tc
27
Co
28
Ni
Ru Rh Pd
Cu
Ag
10 1
88
Ra
IVA
6
C
VA
7
N
VIA
8
O
F
Ne
2s2 2p1 2s2 2p2 2s2 2p3 2s2 2p4 2s2 2p5 2s2 2p6
Mg
Rb Sr
Cs
IIIA
5
VIIA 1s2
9
10
IIA
4
K
DEMO
VIIIA
2
Reducing agent strength: Na > Mg > Al
H
89
Ac#
104 105 106 107 108 109
+
+
+
+
+
+
14
Si
15
P
16
S
17
Cl
18
Ar
IIB 3s2 3p1 3s2 3p2 3s2 3p3 3s2 3p4 3s2 3p5 3s2 3p6
30
31 32
33 34
35 36
Zn
Ga Ge
As
Se
Br
Kr
Cd
In
Sb
Te
I
Xe
Sn
10 2
+ Element
synthesized,
but no official name assigned
7s2 6d1 7s2 6d2 7s2 6d3 7s2 6d4 7s2 6d5 7s2 6d6 7s2 6d7 7s2
4
Part 2 A.
Studies of complex formation with NH3 and OH -.
• Study the reactions of metal aquo complex ions with
Lewis bases (NH3, OH-, …).
Reaction of Lewis Acids (metal ions) with Lewis Bases
• Extent of reaction differs because of acid strength differences.
•Pattern of reactivity with bases (e.g. OH- and NH 3) differs
due to differences in metal ion electron configurations.
1A
VIIIA
1
2
H
He
1 s1
DISCUSSION
• What kinds of observations allow you to infer that a
complexation reaction is occurring?
• Can you predict the reactions of a metal ion based on the
position of its element in the Periodic Table?
3
2s1
11
2s2
12
3s1
19
3s2
20
4s1
37
4s2
38
10 1 10 2
3d1 4 s2 3d2 4 s2 3d3 4 s2 3d5 4 s1 3d5 4 s2 3d6 4 s2 3d7 4 s2 3d8 4 s2 3d 4 s 3d 4 s 4 s2 4 p14 s2 4 p2 4 s2 4 p3 4 s2 4 p4 4 s2 4 p5 4 s2 4 p6
5s1
55
5s2
56
10 1 10 2
4d1 5 s2 4d2 5 s2 4d3 5 s2 4d5 5 s1 4d5 5 s2 4d7 5 s1 4d8 5 s1 4d1 0 4d 5 s 4d 5 s 5 s2 5 p1 5 s2 5 p2 5 s2 5 p3 5 s2 5 p4 5 s2 5 p5 5 s2 5 p6
6s1
87
6s2
88
7s1
7s2
10 1 10 2
5d1 6 s2 5d2 6 s2 5d3 6 s2 5d4 6 s2 5d5 6 s2 5d6 6 s2 5d7 6 s2 5d9 6 s1 5d 6 s 5d 6 s 6 s2 6 p1 6 s2 6 p2 6 s2 6 p3 6 s2 6 p4 6 s2 6 p5 6 s2 6 p6
89
1 0 4 1 0 5 1 0 6 1 0 7 1 0 8 1 0 9 + Element synthesized,
Ac# +
+
+
+
+
+
but no official name assigned
6d1 7 s2 6d2 7 s2 6d3 7 s2 6d4 7 s2 6d5 7 s2 6d6 7 s2 6d7 7 s2
Li
Be
Na
K
Fr
Aquo Complex Ion Reactions
 If reaction occurs with a charged base such as OH-, the
product may be a soluble complex ion or an uncharged
insoluble complex depending on reaction stoichiometry.
B
Sr
Ba
Ra
IVA
6
C
VA
7
N
VIA
8
O
F
Ne
2 s 2 2 p1 2 s 2 2 p2 2 s 2 2 p3 2 s 2 2 p4 2 s 2 2 p5 2 s 2 2 p6
13
Mg
Ca
Rb
Cs
IIIA
5
VIIA 1 s2
9
10
IIA
4
Al
IIIB
21
Sc
39
Y
57
IVB
22
Ti
40
Zr
72
La * Hf
VB
VIB
VIIB VIIIB
⇔ VIIIB
IB
IIB
23
24
25
27
29
30
V
41
Nb
73
Ta
Cr
42
Mn Fe
43
Mo Tc
74
W
26
75
Re
44
Ru
76
Os
Co
45
Rh
77
Ir
28
Ni
46
Pd
78
Pt
Cu
47
Ag
79
Au
Zn
48
Cd
80
Hg
14
Si
15
P
16
S
17
Cl
18
Ar
3 s 2 3 p1 3 s 2 3 p2 3 s 2 3 p3 3 s 2 3 p4 3 s 2 3 p5 3 s 2 3 p6
31
Ga
49
In
81
Tl
32
Ge
50
Sn
82
Pb
33
As
51
Sb
83
Bi
34
Se
52
Te
84
Po
35
Br
53
I
85
At
36
Kr
54
Xe
86
Rn
Aquo Complex Ion Reactions
Example 2: Formation of a insoluble complex:
[Al (H2O)6]3+ + 3OH- → [Al(H2O)3(OH)3] + 3H2O
Example 1: Formation of a soluble complex ion:
[Al (H2O)6]3+ + OH- → [Al(H2O)5(OH)]2+ + H2O
Traditional net precipitation equation:
Al 3+(aq) + 3OH- (aq) → Al(OH)3 (s)
5
[Al (H2O)3(OH)3] + 3OH- → [Al(OH)6]3- + 3 H2O
[Al(H2O)6]3+
↓↑
[Al(H 2O)5(OH)] 2+
↓↑
[Al(H 2O)4(OH) 2] +
↓↑
[Al(H2O)3(OH) 3]
↓↑
[Al(H2O)2(OH) 4]↓↑
[Al(H2O) (OH)5] 2↓↑
[Al(OH) 6]3-
Addition of acid (H+)
Example 3: Addition of more hydroxide ions to the
precipitated hydroxide complex results in formation
of a soluble complex ion:
Addition of Base (NaOH)
Aquo Complex Ion Reactions
 Precipitation reactions are Lewis Acid-Base reactions
DEMO
Reaction of Aquo Metal Complex Ions with NH3
•
If a precipitate forms upon addition of NH 3(aq), the
metal aquo complex ion is reacting with the SMALL
AMOUNT of OH- ions present in NH 3(aq):
NH3(aq) + HOH(l)
NH4+ (aq) + OH - (aq)
 The reactions are reversible equilibrium systems
 The equilibrium point depends on the reactants (strength…)
and reaction conditions (concentration…)
 Lewis acids bond to the best available base.
- an acid does not react (bond) to any base.
“Wanna give me a try?”
[Cu(H2O)4]2+ + NH3 → light blue precipitate*
DEMO
Q. * What is the formula for the hydroxide precipitate?
[Cu(H2O)2(OH)2] (s)
_________________________
Acid-Base
+
Base
→ no reaction
6
 If a better base is available a Lewis acid will
react (exchange partners)!
Q. The acid exchanging base partners is H+.
Which is the BEST base, Cl- or HOH?
Cl-H +
Acid
Acid-Base
+
better Base
→
Reaction
Aquo Complex Ion Reactions
•
•
O
••
H
H
Cl-
H
Base
H
••O
Base
+
H
Acid
H+ bonds to water (best base) rather than Cl-.
• The bonded base-acid product = complex ion.
Aquo Complex Ion Reactions
Example 1: Replacement of water with ammonia molecules.
Example: Replacement of water with ammonia molecules.
[Cu (H2O)4]2+ + 4 NH3 → [Cu(NH3)4]2+ + 4 H2O
DEMO
[Cu(NH3)4]2+
Tetra aquo Cu(II) ion
Tetra ammine Cu(II) ion
Tetrammine copper (II) ion
7
Complex Ions
Aquo Complex Ion Reactions
 Colored transition metal ions alter color upon
bonding to a different Lewis base.
[Cu(H2O)4]2+
 Complex ions are the chemical basis for colorful paint
pigments.
[Cu(NH3)4]2+
 The charge on a complex ion will equal that of the
metal ion when the metal ion is bonded to an
uncharged Lewis base.
Lewis Acid-Base Reactions
Aquo Complex Ion Reactions
Example 2: Replacement of water with chloride ions.
Q. Complete the equation below:
 Complexes react if a better partner (acid or base) is
available so as to form a more stable bond .
[Cu(Cl)4]2- + 4 H2O
[Cu (H2O)4]2+ + 4 Cl- → ___________________
DEMO
Tetra aquo copper(II) ion
Tetra chloro copper(II) ion
The charge on the complex ion alters due to reaction with a
charged Lewis base
Hemoglobin is a complex of Fe that binds to/transports oxygen
8
Aquo Complex Ion Reactions
Example 4: The base ammonia in the Cu(II) product
(ammine complex ion) will react and bond to a better acid
than Cu(II) ions such as H+:
[Cu (H2O)4]2+ + 4 NH3  [Cu(NH3)4]2+ + 4 H2O
Questions?
Contact [email protected]
Q. What will you observe upon adding acid
(H+) to the deep violet-blue ammine product?
DEMO
9