Lecture 223/18/05 Seminar today 4:30 Review: Tomorrow TSC Tonight: 7-8 in Olin Hall room 107 at WPI Sheldon Krimsky from Tufts Relationship between science and ethics, largely pertaining to biotechnology.

REDOX reactions involve ELECTRON TRANSFER Charge and mass balance Half-reactions OXIDATION: atom loses electrons Ca(s)  Ca e - REDUCTION: atom gains electrons 2H + + 2e -  H 2 (g) Combined (net): Ca(s) + 2H +  Ca 2+ + H 2 (g) REDOX REACTIONS Oxidation-Reduction Reaction REDOX REACTIONS Oxidation-Reduction Reaction

OiL Rig Oxidation is Loss Reduction is Gain

An atom that is oxidized also called a reducing agent An atom that is reduced also called an oxidizing agent

OXIDATION OXIDATION NUMBERS Way to keep track of electrons Way to keep track of electrons Positive or negative whole number Positive or negative whole number Equal to the charge that a chemically bonded atom would have if all of the bonding electrons were transferred to the more electronegative atoms Equal to the charge that a chemically bonded atom would have if all of the bonding electrons were transferred to the more electronegative atoms

1. Atoms in elemental state 1. Oxidation # = 0 2. e.g. Zn, O 2, I 2, S 8, H 2, Ca 2. Monatomic ion 1. oxidation # = charge on ion 2. Cl - = -1; K + = +1; Mg 2+ = +2 OXIDATION OXIDATION NUMBERS

3. Reference elements 1. Oxygen: oxidation # usually = peroxides: O 2 2- = -1 (very reactive) 2. Hydrogen 1. Oxidation # = +1 when bound to non-metals 2. Oxidation # = -1 when bound to metals 3. Fluorine: oxidation # = Other halogens: ox. # usually -1, except when bound to oxygen (e.g. ClO 4 - ) OXIDATION OXIDATION NUMBERS

4. Sum of all oxidation numbers 1. = 0 for a neutral compound 2. = overall charge for an ion OXIDATION OXIDATION NUMBERS

OXIDATION NUMBERS NH 3 N = ClO - Cl = H 3 PO 4 P = MnO 4 - Mn = Cr 2 O 7 2- Cr = C 3 H 8 C =

Balancing Redox reactions H 2 C 2 O 4 (aq) + MnO 4 -  Mn 2+ + CO 2 (g) oxalic acid permanganate 1. Break into half-reactions 1. H 2 C 2 O 4 (aq)  CO 2 (g) 2. MnO 4 -  Mn 2+ oxidation reduction

Balancing Redox reactions H 2 C 2 O 4 (aq) + MnO 4 -  Mn 2+ + CO 2 (g) oxalic acid permanganate Balance the atoms 1. Balance the non H, O atoms first H 2 C 2 O 4 (aq)  CO 2 (g) MnO 4 -  Mn 2+

Balancing Redox reactions H 2 C 2 O 4 (aq) + MnO 4 -  Mn 2+ + CO 2 (g) oxalic acid permanganate Balance the atoms 1. Balance the non H, O atoms first 2. Balance O with H 2 O H 2 C 2 O 4 (aq)  2CO 2 (g) MnO 4 -  Mn 2+

Balancing Redox reactions H 2 C 2 O 4 (aq) + MnO 4 -  Mn 2+ + CO 2 (g) oxalic acid permanganate Balance the atoms 1. Balance the non H, O atoms first 2. Balance O with H 2 O 3. Balance H with H + H 2 C 2 O 4 (aq)  2CO 2 (g) MnO 4 -  Mn H 2 O

Balancing Redox reactions H 2 C 2 O 4 (aq) + MnO 4 -  Mn 2+ + CO 2 (g) oxalic acid permanganate Balance the atoms 1. Balance the non H, O atoms first 2. Balance O with H 2 O 3. Balance H with H + 4. Balance charge with e - H 2 C 2 O 4 (aq)  2CO 2 (g) + 2H + 8H + + MnO 4 -  Mn H 2 O

Balancing Redox reactions H 2 C 2 O 4 (aq) + MnO 4 -  Mn 2+ + CO 2 (g) oxalic acid permanganate Balance the atoms 1. Balance the non H, O atoms first 2. Balance O with H 2 O 3. Balance H with H + 4. Balance charge with e - 5. Multiply half-reactions to balance electrons H 2 C 2 O 4 (aq)  2CO 2 (g) + 2H + + 2e - 5e - + 8H + + MnO 4 -  Mn H 2 O

Balancing Redox reactions H 2 C 2 O 4 (aq) + MnO 4 -  Mn 2+ + CO 2 (g) oxalic acid permanganate Balance the atoms 1. Balance the non H, O atoms first 2. Balance O with H 2 O 3. Balance H with H + 4. Balance charge with e - 5. Multiply half-reactions to balance electrons 5 × (H 2 C 2 O 4 (aq)  2CO 2 (g) + 2H + + 2e - ) 2 × (5e - + 8H + + MnO 4 -  Mn H 2 O) 5H 2 C 2 O 4 + 6H + + 2MnO 4 -  10CO 2 (g) + 8H 2 O + 2Mn 2+

Balancing Redox reactions H 2 C 2 O 4 (aq) + MnO 4 -  Mn 2+ + CO 2 (g) oxalic acid permanganate Check for mass and charge balance 5H 2 C 2 O 4 + 6H + + 2MnO 4 -  10CO 2 (g) + 8H 2 O 2Mn 2+