Aqueous and Nonaqueous Solvents Solvent Considerations

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Aqueous and Nonaqueous SolventsSolvent
Considerations

• Edward A. Mottel
• Department of Chemistry
• Rose-Hulman Institute of Technology

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Solvents
Solvents affect solubility and reactivity.
Reactions are pH dependent.
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Solvation ConsiderationsEnergetics
Solution will occur if
solute-solute solvent-solvent interaction
solute-solvent interaction
gt
Enthalpy and entropy terms are both important.
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Solvation ConsiderationsEnthalpy
NaCl(s) ?? Na(aq) Cl-(aq)
formation of new ion-dipole bonds
lattice energy solvent H-bonds
DHsolution DHsolute-solvent - DHsolute-solute -
DHsolvent-solvent
Under what conditions will heating a solution
increase solubility?
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Solvation ConsiderationsEntropy
NaCl(s) ?? Na(aq) Cl-(aq)
net gain in particles
Actual entropy may go down because of solvent
coordination and orientation.
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Solvation ConsiderationsCoordination Ability
donor and acceptor properties, high ?o
H2O
NH3
better donor, poorer acid than water.
HF
better acid but poorer donor than water.
DMSO
good base, but no acidic hydrogen atoms to act as
a Lewis acid
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Solvation ConsiderationsCoordination Ability
H2O
BaCl2(s) 2 AgNO3(am)
2 AgCl(s) Ba(NO3)2(aq)
NH3
H2O solvates Ba2
NH3 solvates Ag
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Metal-Ammonia Solutions
Metals with oxidation potentials gt2.5 V
dissolve in liquid ammonia to form solutions.
NH3
Na(s) ?? Na(am) e-(am)
bright blue
all metals give the same blue color
good electrical conductors
very dilute solutions equivalent conductance
better than metal high magnetic susceptibility
(unpaired e-)
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Metal-Ammonia Solutions
Factors required of metal
Na(g) e-
DHsolvation e-
high solvation energy
Na(g)
low ionization potential
low sublimation energy
Na(s)
DHsolvation Na
Na(am) e-(am)
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Metal-Ammonia Solutions
Metals with oxidation potentials gt2.5 V
dissolve in liquid ammonia to form solutions.
NH3
Na(s) ?? Na(am) e-(am)
bronze
concentrated solutions good electrical
conductors (similar to metal) mole ratio
ammonia/metal 51 to 101 lower magnetic
susceptibility (e-pairing)
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Electrode Potential EMF and Free Energy
E cell E ½,anode E ½,cathode
Nernst Equation
DG - nFE
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Electrode Potential pH Dependence
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Electrode Potential pH Dependence
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Half-Cell Potentials Latimer Diagrams
What happens when chlorine gas is dissolved in
alkaline water?
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Half-Cell Potentials Latimer Diagrams
0.36
0.33
0.66
0.40
1.36
ClO4-
ClO3-
ClO2-
ClO-
Cl2
Cl-
0.50
0.88
E½ - 0.40 V
Ecell 0.96 V
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Half-Cell Potentials Latimer Diagrams
0.36
0.33
0.66
0.40
1.36
ClO4-
ClO3-
ClO2-
ClO-
Cl2
Cl-
0.50
0.88
What is the half-cell potential for ClO3- ? Cl2 ?
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ClO-
DG - nFE
DG - nFE
???
???
ClO3- ?????? Cl2
DG - nFE
Balance each half cell reaction.
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ClO-
8 e- 4 H2O 2 ClO3- ? 2 ClO- 8 OH-

• 2 e- 2 H2O 2 ClO-
• Cl2 4 OH-

???
???
ClO3- ?????? Cl2
10 e- 6 H2O 2 ClO3- ? Cl2 12 OH-
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ClO-
DG - 8 F (0.50V)
DG - 2 F (0.40 V)
???
???
ClO3- ?????? Cl2
DG - 10 F E
DG - 10 F E - 8 F (0.50V) - 2 F (0.40 V)
E - (- 4.0 F 0.8 F ) / 10 F 0.48 V
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DG - nFE
DG1 - 2 F (0.40)
DG2 - 2 F (1.36)
DG12 - 4 F (E?) -0.80 F 2.72 F
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