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