aqueous and nonaqueous solvents solvent considerations edward a. mottel department of chemistry...
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Aqueous and Nonaqueous Solvents
Solvent Considerations
Edward A. Mottel
Department of Chemistry
Rose-Hulman Institute of Technology
04/18/23
Solvents
Solvents affect solubility and reactivity.
Reactions are pH dependent.
Solvation ConsiderationsEnergetics
Solution will occur if
solute-solventinteraction
>solute-solute &solvent-solvent
interaction
Enthalpy and entropy terms are both important.
Solvation ConsiderationsEnthalpy
NaCl(s) Na+(aq) + Cl-(aq)
formation of newion-dipole bonds
lattice energysolvent H-bonds
high for water(81.7 o)
Hsolution = Hsolute-solvent - Hsolute-solute - Hsolvent-solvent
Under what conditions will heating a solution increase solubility?
Solvation ConsiderationsEntropy
NaCl(s) Na+(aq) + Cl-(aq)
net gain in particles
Actual entropymay go down because of
solvent coordination and orientation.
Solvation ConsiderationsCoordination Ability
NH3 better donor, poorer acid than water.
HF better acid but poorer donor than water.
DMSOgood base, but no acidic hydrogen atomsto act as a Lewis acid
H2O donor and acceptor properties, high o
04/18/23
BaCl2(s) + 2 AgNO3(am) 2 AgCl(s) + Ba(NO3)2(aq)H2O
NH3
H2O solvates Ba2+NH3 solvates Ag+
Solvation ConsiderationsCoordination Ability
Metal-Ammonia Solutions
Metals with oxidation potentials >2.5 V dissolvein liquid ammonia to form solutions.
Na(s) Na+(am) + e-(am) NH3
bright blueall metals
give the sameblue color
good electrical conductors
very dilute solutions:equivalent conductance better than metalhigh magnetic susceptibility (unpaired e-)
Metal-Ammonia Solutions
Factors requiredof metal
high solvation energy
low ionization potential
low sublimation energy
Na+(g) + e-
Na(s)
Na(g)
Na+(am) + e-(am)
Hsolvation e-
Hsolvation Na+
Metal-Ammonia Solutions
Metals with oxidation potentials >2.5 V dissolvein liquid ammonia to form solutions.
Na(s) Na+(am) + e-(am) NH3
bronze
concentrated solutions:good electrical conductors (similar to metal)mole ratio ammonia/metal = 5:1 to 10:1lower magnetic susceptibility (e-pairing)
Electrode Potential EMF and Free Energy
E °cell = E °½,anode + E °½,cathode
0.0592n
products
reactants· logEcell = E °cell -
G = - nFE
e-
transferredcharge of a mole of e-
96,485 C
Nernst Equation
Electrode Potential pH Dependence
2 H3O+(pH=0) + 2 e- 2 H2O + H2(g)E½°= 0.00 V
2 H3O+ (neutral) + 2 e- 2 H2O + H2(g)E½ = -0.414 V
2 H3O+ (pH=14) + 2 e- 2 H2O + H2(g)E½ = -0.828 V
Electrode Potential pH Dependence
2 H3O+(pH=0) + 2 e- 2 H2O + H2(g)E½°= 0.00 V
2 H3O+ (neutral) + 2 e- 2 H2O + H2(g)E½ = -0.414 V
0.05922
PH2
[H3O+]2
· logE½ = E½° -
Half-Cell Potentials Latimer Diagrams
What happens when chlorine gasis dissolved in alkaline water?
Cl2(g) + H2O(l)
Half-Cell Potentials Latimer Diagrams
ClO4- ClO3
- ClO2- ClO- Cl2 Cl-
0.36 0.33 0.66 0.40 1.36
0.50 0.88
E½° = +1.36 V2 e- + Cl2(g) 2 Cl-
E½° = - 0.40 V4 OH- + Cl2(g) 2 ClO- + 2 H2O + 2 e-
Ecell° = +0.96 V
Half-Cell Potentials Latimer Diagrams
ClO4- ClO3
- ClO2- ClO- Cl2 Cl-
0.36 0.33 0.66 0.40 1.36
0.50 0.88
What is the half-cell potential for ClO3- Cl2 ?
ClO3- Cl2
ClO-
Balance each half cell reaction.
G = - nFE G = - nFE
G = - nFE
ClO3- Cl2
10 e- + 6 H2O + 2 ClO3- Cl2 + 12 OH-
ClO-
8 e- + 4 H2O + 2 ClO3-
2 ClO- + 8 OH-
2 e- + 2 H2O + 2 ClO-
Cl2 + 4 OH-
ClO3- Cl2
ClO-
G = - 8 F (+0.50V) G = - 2 F (+0.40 V)
G = - 10 F E
E = - (- 4.0 F – 0.8 F ) / 10 F = 0.48 V
G = - 10 F E = - 8 F (+0.50V) + - 2 F (+0.40 V)
G = - nFE
G1 = - 2 F (0.40)
G2 = - 2 F (1.36)
G12 = - 4 F (E?) = -0.80 F – 2.72 F