Pre-lab (p.141) due at start of lab. Problem Compounds ...chem125/W08/E5W08lab1key.pdf · 1 E5...
Transcript of Pre-lab (p.141) due at start of lab. Problem Compounds ...chem125/W08/E5W08lab1key.pdf · 1 E5...
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E5 Lewis Acids and Bases
Session oneSession onePre-lab (p.141) due at start of lab.Pre-lab (p.141) due at start of lab.Hour 1: Discussion of E4Hour 1: Discussion of E4Hours 2 & 3: Lab (Parts 1andHours 2 & 3: Lab (Parts 1and 2A)2A)
Session twoLab: Parts 2B, 3 and 4
Acids
Bronsted: Acids are proton donors.
DEMO
Problem• Compounds containing cations other than H+
are acids!
Acids
Example: Al3+ (aq) = ≈ pH 3!
Deodorants and acid loving plant foods contain aluminum salts
Cations other than H+ generate hydroniumions in aqueous solution!
Lewis Definition of Acids and Bases
A BASE DONATES unbonded ELECTRON PAIR/S. An ACID ACCEPTS ELECTRON PAIR/S .
Acid Base Base Acid
HCl-H + ••O
• • H
Cl- H H + • O
• H
Define acid/base without using the word proton:
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Lewis Acids
Electron deficient species ; potential electronpair acceptors.
Examples: H+ Cu2+ Al3+
“I’m deficient!”
Acid
Lewis Bases
Electron rich species; electron pair donors.
(ammine) (hydroxo) (aquo)Ammonia hydroxide ion water__
Lewis Acid-Base Reactions
The acid reacts with the base by bonding to one ormore available electron pairs on the base.
Acid + Base Complex ion
H H+ + ••O
• • H
H H + • O
• H
Example
The acid-base bond is a coordinate covalent bond. The product is a complex or complex ion
Lewis Acids: Metal Ions
Metal ions react with/bond to water molecules toform aquo complex ions in aqueous solution.
• Example: [Na(H2O)6]+
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Aquo Complex Ions
Example: CuSO4 (s) → Cu2+(aq) + SO4
2- (aq)
[Cu(H2O)4]2+
When a salt dissolves, the metal ions in the salt solution reactwith/bond to water molecules to forms aquo complex ions.
Aquo Complex Ions
Examples
[Pb(H2O)4]2+
Tetra aquo lead ion[Ni(H2O)6]2+
Hexa aquo nickel ion
[Cu(H2O)4]2+
Tetra aquo copper(II)ion[H(H2O)]+
Hydronium ion
Colored aquo complex ions contain a transitionmetal ion with incompletely filled d orbitals.
Part 1. Acidity of Cations
Collect pH data for different metal aquo complexions in aqueous solution.• pH versus periodic table position of ion’s metal?• pH versus metal ion size and charge? extent of s’
• Study the reaction of metal aquo complex ions withthe Lewis base H2O to produce hydronium ions.
Metal Ion Acid Strength
The acid strength of a metal ion is dependent on itsability to attract electrons (oxidizing agent strength)
∝ + HMx+ O H
....∝ +
The greater the acid strength of a metal ion the morepolarized the bonded water molecules (and electrondeficient the protons) in the aquo complex ion.
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Electron deficient proton/s in the polarized watermolecules of the metal aquo complex ion react andbond to an electron pair in another water molecule
Reactions of Metal Aquo Complex Ions with Water
Reaction of Metal Aquo Complex Ion:
[Al (H2O)6]3+ + H2O → [Al(H2O)5(OH)]2+ + [H-H2O]+
When a proton bonds to a water molecule, a H3O+
ion is formed.
Q. Complete a balanced equation to show formation of hydronium ions:
+ 2 [H3O]+[Al(H2O)4(OH)2]+[Al(H2O)6]3+ + 2 HOH →
Metal Ion Acid Strength
Q. Given the reducing agent strength Na > Mg > Al,indicate the Lewis acid strength of Na+, Mg2+, and Al3+
Metal Ion Acid Strength: ___________________Al3+ > Mg2+ > Na+
DEMO
1A VIIIA
1H
1s1 IIA IIIA IVA VA VIA VIIA
2He1s2
3Li
2s1
4Be
2s2
5B
2s22p1
6C
2s22p2
7N
2s22p3
8O
2s22p4
9F
2s22p5
1 0Ne
2s22p6
1 1Na
3s1
1 2Mg
3s2 IIIB IVB VB VIB VIIB VIIIB ! VIIIB IB IIB
1 3Al
3s23p1
1 4Si
3s23p2
1 5P
3s23p3
1 6S
3s23p4
1 7Cl
3s23p5
1 8Ar
3s23p6
1 9K
4s1
2 0Ca
4s2
2 1Sc
3d14s2
2 2Ti
3d24s2
2 3V
3d34s2
2 4Cr
3d54s1
2 5Mn
3d54s2
2 6Fe
3d64s2
2 7Co
3d74s2
2 8Ni
3d84s2
2 9Cu
3d1 04s1
3 0Zn
3d1 04s2
3 1Ga
4s24p1
3 2Ge
4s24p2
3 3As
4s24p3
3 4Se
4s24p4
3 5Br
4s24p5
3 6Kr
4s24p6
3 7Rb
5s1
3 8Sr
5s2
3 9Y
4d15s2
4 0Zr
4d25s2
4 1Nb
4d35s2
4 2Mo
4d55s1
4 3Tc
4d55s2
4 4Ru
4d75s1
4 5Rh
4d85s1
4 6Pd
4d10
4 7Ag
4d1 05s1
4 8Cd
4d1 05s2
4 9In
5s25p1
5 0Sn
5s25p2
5 1Sb
5s25p3
5 2Te
5s25p4
5 3I
5s25p5
5 4Xe
5s25p6
5 5Cs
6s1
5 6Ba
6s2
5 7
La*
5d16s2
7 2Hf
5d26s2
7 3Ta
5d36s2
7 4W
5d46s2
7 5Re
5d56s2
7 6Os
5d66s2
7 7Ir
5d76s2
7 8Pt
5d96s1
7 9Au
5d1 06s1
8 0Hg
5d1 06s2
8 1Tl
6s26p1
8 2Pb
6s26p2
8 3Bi
6s26p3
8 4Po
6s26p4
8 5At
6s26p5
8 6Rn
6s26p6
8 7Fr
7s1
8 8Ra
7s2
8 9Ac#
6d17s2
1 0 4 +
6d27s2
1 0 5 +
6d37s2
1 0 6 +
6d47s2
1 0 7 +
6d57s2
1 0 8 +
6d67s2
1 0 9 +
6d77s2
+ Element synthesized,
but no official name assigned
Aquo Complex Ion Reactions
Acid strength
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Part 2 A.Studies of complex formation with NH3 and OH -.
• Study the reactions of metal aquo complex ions withLewis 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
1A VIIIA
1H
1s1 IIA IIIA IVA VA VIA VIIA
2He1s2
3Li
2s1
4Be
2s2
5B
2s22p1
6C
2s22p2
7N
2s22p3
8O
2s22p4
9F
2s22p5
1 0Ne
2s22p6
1 1Na
3s1
1 2Mg
3s2 IIIB IVB VB VIB VIIB VIIIB ! VIIIB IB IIB
1 3Al
3s23p1
1 4Si
3s23p2
1 5P
3s23p3
1 6S
3s23p4
1 7Cl
3s23p5
1 8Ar
3s23p6
1 9K
4s1
2 0Ca
4s2
2 1Sc
3d14s2
2 2Ti
3d24s2
2 3V
3d34s2
2 4Cr
3d54s1
2 5Mn
3d54s2
2 6Fe
3d64s2
2 7Co
3d74s2
2 8Ni
3d84s2
2 9Cu
3d1 04s1
3 0Zn
3d1 04s2
3 1Ga
4s24p1
3 2Ge
4s24p2
3 3As
4s24p3
3 4Se
4s24p4
3 5Br
4s24p5
3 6Kr
4s24p6
3 7Rb
5s1
3 8Sr
5s2
3 9Y
4d15s2
4 0Zr
4d25s2
4 1Nb
4d35s2
4 2Mo
4d55s1
4 3Tc
4d55s2
4 4Ru
4d75s1
4 5Rh
4d85s1
4 6Pd
4d10
4 7Ag
4d1 05s1
4 8Cd
4d1 05s2
4 9In
5s25p1
5 0Sn
5s25p2
5 1Sb
5s25p3
5 2Te
5s25p4
5 3I
5s25p5
5 4Xe
5s25p6
5 5Cs
6s1
5 6Ba
6s2
5 7
La*
5d16s2
7 2Hf
5d26s2
7 3Ta
5d36s2
7 4W
5d46s2
7 5Re
5d56s2
7 6Os
5d66s2
7 7Ir
5d76s2
7 8Pt
5d96s1
7 9Au
5d1 06s1
8 0Hg
5d1 06s2
8 1Tl
6s26p1
8 2Pb
6s26p2
8 3Bi
6s26p3
8 4Po
6s26p4
8 5At
6s26p5
8 6Rn
6s26p6
8 7Fr
7s1
8 8Ra
7s2
8 9Ac#
6d17s2
1 0 4 +
6d27s2
1 0 5 +
6d37s2
1 0 6 +
6d47s2
1 0 7 +
6d57s2
1 0 8 +
6d67s2
1 0 9 +
6d77s2
+ Element synthesized,
but no official name assigned
• Extent of reaction differs because of acid strength differences.
Reaction of Lewis Acids (metal ions) with Lewis Bases
•Pattern of reactivity with bases (e.g. OH- and NH3) differsdue to differences in metal ion electron configurations.
If reaction occurs with a charged base such as OH-, theproduct may be a soluble complex ion or an unchargedinsoluble complex depending on reaction stoichiometry.
Metal Aquo Complex Ion Reactions with OH-
Example 1: Formation of a soluble complex ion:
[Al (H2O)6]3+ + OH- → [Al(H2O)5(OH)]2+ + H2O
Aquo Complex Ion Reactions with OH-
Example 2: Formation of a insoluble complex:
[Al (H2O)6]3+ + 3OH- → [Al(H2O)3(OH)3] + 3H2O
Traditional net precipitation equation:Al 3+(aq) + 3OH- (aq) → Al(OH)3 (s)
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Aquo Complex Ion Reactions with OH-
Example 3: Addition of excess hydroxide ions to theprecipitated hydroxide complex results in formationof a soluble complex ion:
[Al (H2O)3(OH)3] + 3OH- → [Al(OH)6]3- + 3 H2O
DEMO
[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-
Add
ition
of B
ase
(NaO
H)
Precipitation reactions are Lewis Acid-Base reactions The reactions are reversible equilibrium systems The equilibrium point depends on the reactants (strength…)and reaction conditions (concentration…)
Add
ition
of a
cid
(H+)
• If a precipitate forms upon addition of NH3(aq), themetal aquo complex ion is reacting with the SMALLAMOUNT of OH- ions present in NH3(aq):
NH3(aq) + HOH(l) NH4+ (aq) + OH- (aq)
Reaction of Aquo Metal Complex Ions with NH3
[Cu(H2O)4]2+ + NH3 → light blue precipitate*
DEMO
Q. * What is the formula for the hydroxide precipitate?_________________________[Cu(H2O)2(OH)2] (s)
Lewis acids bond to the best available base. - an acid does not react (bond) to any base.
+ Base → no reaction
“Wanna give me a try?”
Acid-Base
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If a better base is available a Lewis acid willreact (exchange partners)!
Acid-Base + better Base → Reaction
Q. The acid exchanging base partners is H+. Which is the BEST base, Cl- or HOH?
Acid Base Base Acid
HCl-H + ••O
• • H
Cl- H H + • O
• H
H+ bonds to water (best base) rather than Cl-.
• The bonded base-acid product = complex ion.
Example 1: Replacement of water with ammonia molecules.
Aquo Complex Ion Replacement Reactions
[Cu (H2O)4]2+ + 4 NH3 → [Cu(NH3)4]2+ + 4 H2O
DEMO
Tetra aquo Cu(II) ion Tetra ammine Cu(II) ion
Example: Replacement of water with ammonia molecules.
Aquo Complex Ion Reactions
[Cu(NH3)4]2+
Tetrammine copper (II) ion
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Complex Ions
Complex ions are the chemical basis for colorful paintpigments.
Aquo Complex Ion Reactions
[Cu(NH3)4]2+[Cu(H2O)4]2+
Colored transition metal ions alter color uponbonding to a different Lewis base.
The charge on a complex ion will equal that of themetal ion when the metal ion is bonded to anuncharged Lewis base such as H2O or NH3.
Example 2: Replacement of water with chloride ions. Q. Complete the equation below:
Aquo Complex Ion Replacements Reactions
[Cu (H2O)4]2+ + 4 Cl- → ___________________
DEMO
Tetra aquo copper(II) ion Tetra chloro copper(II) ion
[Cu(Cl)4]2- + 4 H2O
The charge on the complex ion alters due to reaction with acharged Lewis base
Lewis Acid-Base Reactions
Complexes react if a better partner (acid or base) isavailable so as to form a more stable bond.
Hemoglobin is a complex of Fe that binds to/transports oxygen
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Example 4: The base ammonia in the Cu(II) product(ammine complex ion) will react and bond to a better acidthan Cu(II) ions such as H+:
Aquo Complex Ion Replacement Reactions
[Cu (H2O)4]2+ + 4 NH3 [Cu(NH3)4]2+ + 4 H2O
DEMOQ. What will you observe upon adding acid(H+) to the deep violet-blue ammine product?
Questions?Contact [email protected]