1. Aqueous and Nonaqueous Solvents Solvent Considerations Edward A. Mottel Department of Chemistry Rose-Hulman Institute of Technology

2. 6/26/2015 Solvents Solvents affect solubility and reactivity. Reactions are pH dependent.

3. Solvation Considerations Energetics Solution will occur if solute-solvent interaction > solute-solute & solvent-solvent interaction Enthalpy and entropy terms are both important.

4. Solvation Considerations Enthalpy NaCl(s)  Na + (aq) + Cl - (aq) formation of new ion-dipole bonds lattice energy solvent H-bonds high  for water (81.7  o )  H solution =  H solute-solvent -  H solute-solute -  H solvent-solvent Under what conditions will heating a solution increase solubility?

5. Solvation Considerations Entropy NaCl(s)  Na + (aq) + Cl - (aq) net gain in particles Actual entropy may go down because of solvent coordination and orientation.

6. Solvation Considerations Coordination Ability NH 3 better donor, poorer acid than water. HFbetter acid but poorer donor than water. DMSOgood base, but no acidic hydrogen atoms to act as a Lewis acid H2OH2O donor and acceptor properties, high  o

7. 6/26/2015 BaCl 2 (s) + 2 AgNO 3 (am)2 AgCl(s) + Ba(NO 3 ) 2 (aq) H2OH2O NH 3 H 2 O solvates Ba 2+ NH 3 solvates Ag + Solvation Considerations Coordination Ability

8. Metal-Ammonia Solutions Metals with oxidation potentials >2.5 V dissolve in liquid ammonia to form solutions. Na(s)  Na + (am) + e - (am) NH 3 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 - )

9. Metal-Ammonia Solutions Factors required of metal high solvation energy low ionization potential low sublimation energy Na + (g) + e - Na(s) Na(g) Na + (am) + e - (am)  H solvation e -  H solvation Na +

10. Metal-Ammonia Solutions Metals with oxidation potentials >2.5 V dissolve in liquid ammonia to form solutions. Na(s)  Na + (am) + e - (am) NH 3 bronze concentrated solutions: good electrical conductors (similar to metal) mole ratio ammonia/metal = 5:1 to 10:1 lower magnetic susceptibility (e - pairing)

11. Electrode Potential EMF and Free Energy E ° cell = E ° ½,anode + E ° ½,cathode 0.0592 n products reactants · log E cell = E ° cell -  G = - n F E e - transferred charge of a mole of e - 96,485 C Nernst Equation

12. Electrode Potential pH Dependence 2 H 3 O + (pH=0) + 2 e - 2 H 2 O + H 2 (g) E ½ °= 0.00 V 2 H 3 O + (neutral) + 2 e - 2 H 2 O + H 2 (g) E ½ = -0.414 V 2 H 3 O + (pH=14) + 2 e - 2 H 2 O + H 2 (g) E ½ = -0.828 V

13. Electrode Potential pH Dependence 2 H 3 O + (pH=0) + 2 e - 2 H 2 O + H 2 (g) E ½ °= 0.00 V 2 H 3 O + (neutral) + 2 e - 2 H 2 O + H 2 (g) E ½ = -0.414 V 0.0592 2 PH2PH2 [H3O+]2[H3O+]2 · log E ½ = E ½ ° -

14. Half-Cell Potentials Latimer Diagrams What happens when chlorine gas is dissolved in alkaline water? Cl 2 (g) + H 2 O( l )

15. Half-Cell Potentials Latimer Diagrams ClO 4 - ClO 3 - ClO 2 - ClO - Cl 2 Cl - 0.360.330.660.401.36 0.500.88 E ½ ° = +1.36 V 2 e - + Cl 2 (g) 2 Cl - E ½ ° = - 0.40 V 4 OH - + Cl 2 (g) 2 ClO - + 2 H 2 O + 2 e - E cell ° = +0.96 V

16. Half-Cell Potentials Latimer Diagrams ClO 4 - ClO 3 - ClO 2 - ClO - Cl 2 Cl - 0.360.330.660.401.36 0.500.88 What is the half-cell potential for ClO 3 -  Cl 2 ?

17. ClO 3 -  Cl 2  ClO - Balance each half cell reaction.  G = - n F E

18. ClO 3 -  Cl 2 10 e - + 6 H 2 O + 2 ClO 3 -  Cl 2 + 12 OH -  ClO - 8 e - + 4 H 2 O + 2 ClO 3 -  2 ClO - + 8 OH - 2 e - + 2 H 2 O + 2 ClO -  Cl 2 + 4 OH -

19. ClO 3 -  Cl 2  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)

21.  G = - nF E  G 1 = - 2 F (0.40)  G 2 = - 2 F (1.36)  G 12 = - 4 F ( E? ) = -0.80 F – 2.72 F