Acids
E5 Lewis Acids and Bases
Bronsted: Acids are proton donors.
Session one
Pre-lab (p.141) due at start of lab.
Hour 1: Discussion of E4
Hours 2 & 3: Lab (Parts 1and 2A)
Session two
Lab: Parts 2B, 3 and 4
Acids
Problem
• Compounds containing cations other than H+
are acids!
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:
Example: Al3+ (aq) = ≈ 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 Acids: Metal Ions
 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 the salt 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
x+ ..
M
.. O
H∝ +
H∝ +
 The acid strength of a metal ion is dependent on its
ability to attract electrons (oxidizing agent strength)
 The greater the acid strength of a metal ion the more
polarized the bonded water molecules (and electron
deficient the protons) 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.
Aquo Complex Ion Reactions
Metal Ion Acid Strength
Acid strength
Q. Given the reducing agent strength Na > Mg > Al,
indicate the Lewis acid strength of Na+, Mg2+, and Al3+
1A
1
1 s1
Al3+ > Mg2+ > Na+
Metal Ion Acid Strength: ___________________
He
IIA
4
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 4s 3d 4s 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 5s 4d 5s 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
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 6s 5d 6s 6 s2 6 p1 6 s2 6 p2 6 s2 6 p3 6 s2 6 p4 6 s2 6 p5 6 s2 6 p6
8 9 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
K
Rb
Cs
Fr
IIIA
5
Be
B
Sr
Ba
Ra
C
VA
7
N
VIA
8
O
F
Ne
2 s2 2 p1 2 s2 2 p2 2 s2 2 p3 2 s2 2 p4 2 s2 2 p5 2 s2 2 p6
13
Mg
Ca
IVA
6
VIIA 1 s2
9
10
3
Na
DEMO
VIIIA
2
H
Al
IIIB
IVB VB
VIB VIIB VIIIB ! VIIIB
IB
IIB
21
22
24
29
30
Sc
39
Y
57
Ti
40
Zr
72
La* Hf
23
V
41
Cr
42
25
Mn Fe
43
Nb Mo Tc
73
Ta
74
W
26
75
Re
44
Ru
76
Os
27
Co
45
Rh
77
Ir
28
Ni
46
Pd
78
Pt
Cu
10
Ga
49
Cd
79
Au
31
48
Ag
In
80
1
Hg
10
Si
15
P
16
S
17
Cl
18
Ar
3 s2 3 p1 3 s2 3 p2 3 s2 3 p3 3 s2 3 p4 3 s2 3 p5 3 s2 3 p6
Zn
47
14
81
2
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
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-, …).
DISCUSSION
• What kinds of observations allow you to infer that a
complexation reaction is occurring?
• Predict the reactions of a metal ion with Lewis bases
based on the position of its element in the Periodic Table
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 NH3) differs
due to differences in metal ion electron configurations.
1A
VIIIA
1
2
H
He
1 s1
IIA
IIIA
IVA
VA
VIA
VIIA 1 s2
3
4
5
6
7
8
9
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
Cs
Fr
Metal Aquo Complex Ion Reactions with OH 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.
13
Mg
Ca
Rb
B
Sr
Ba
Ra
C
N
O
F
10
Ne
2 s2 2 p1 2 s2 2 p2 2 s2 2 p3 2 s2 2 p4 2 s2 2 p5 2 s2 2 p6
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 s2 3 p1 3 s2 3 p2 3 s2 3 p3 3 s2 3 p4 3 s2 3 p5 3 s2 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 with OHExample 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(H2O)5(OH)]2+
↓↑
[Al(H2O)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 excess hydroxide ions to the
precipitated hydroxide complex results in formation
of a soluble complex ion:
Addition of Base (NaOH)
Aquo Complex Ion Reactions with OH-
 Precipitation reactions are Lewis Acid-Base reactions
DEMO
Reaction of Aquo Metal Complex Ions with NH3
•
If a precipitate forms upon addition of NH3 (aq), the
metal aquo complex ion is reacting with the SMALL
AMOUNT of OH- ions present in NH3(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 Replacement Reactions
Example 1: Replacement of water with ammonia molecules.
•
•
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: Replacement of water with ammonia molecules.
[Cu (H 2O)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.
Aquo Complex Ion Replacements Reactions
Example 2: Replacement of water with chloride ions.
Q. Complete the equation below:
[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 such as H2O or NH3.
Lewis Acid-Base Reactions
 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 (H 2O)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 Replacement 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 (H 2O)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