Redox Reactions. Sections 4.9, RW Session ID = MSTCHEM1

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1 Redox Reactions Sections 4.9, 18.2 RW Session ID = MSTCHEM1

2 Oxidation Reduction Reactions Redox Reactions Electrons are transferred from one reactant to another Oxidation loss of electrons Reduction gain of electrons OIL RIG LEO GER Oxidation is Is Loss of electrons Reduction Is Gain of electrons Loss of Electrons is Oxidation Gain of Electrons is Reduction

3 Rules for Assigning Oxidation States Free element (neutral and not bonded to another element) 0 Monoatomic ion charge In compounds, metals have positive oxidation states: Group 1A metals +1 Group 2A metals +2 In compounds: Fluorine 1 Hydrogen +1 (when bonded to nonmetals) or 1 (when bonded to metals) Oxygen 2 (except w/fluorine or bonded to itself) The sum of the oxidation states: Neutral molecule 0 Polyatomic ion charge Ionic compounds can be broken into the corresponding ions and treated separately These rules give you a starting place for assigning oxidation states. You should start at the top and work your way down. All other oxidation states can be determined by knowing that the sum of oxidation states equals the charge on the substance.

4 Oxidation States K Ca O 2 Cl 2 P K + Ca 2+ O 2 Clˉ P Hg 2+ Hg 2+ 2 NO 2ˉ SO 2 4 Cr 2 O 2 7

5 Oxidation States LiBr CaS CuO Cu 2 O Mg 3 N BaSO 4 Na 3 PO 3 Fe(OH) 2 Sn(BrO 2 ) NO NO 2 BrF 3 P 2 H 4 S 2 O

6 Redox Reactions Oxidation and Reduction Loss of electrons and gain of electrons Change in oxidation states from reactant to product Oxidizing agent (oxidant, oxidizer) A substance that causes the oxidation of another substance. gains electrons, is reduced Reducing agent (reductant, reducer) A substance that causes the reduction of another substance loses electrons, is oxidized

7 Determine whether each of the following reactions are redox reactions. If so, identify the oxidant and reductant Al 3+ (aq) + Cu + (aq) Al(s) + Cu 2+ (aq) reduction oxidation Cu + reductant Al 3+ oxidant HCl(aq) + Ca(OH) 2 (aq) CaCl 2 (aq) + H 2 O(l) not a redox reaction

8 Determine whether each of the following reactions are redox reactions. If so, identify the oxidant and reductant Ca(s) + O 2 (g) CaO(s) oxidation reduction Ca reductant O 2 oxidant NaCl(aq) + AgNO 3 (aq) NaNO 3 (aq) + AgCl(s) not a redox reaction

9 Determine whether each of the following reactions are redox reactions. If so, identify the oxidant and reductant NaCl(aq) + F 2 (g) NaF(aq) + Cl 2 (g) oxidation reduction NaCl reductant F 2 oxidant C 3 H 6 (l) + O 2 (g) CO 2 (g) + H 2 O(g) oxidation reduction C 3 H 6 reductant O 2 oxidant

10 Determine whether each of the following reactions are redox reactions. If so, identify the oxidant and reductant Fe 2+ (aq) + Cr 2 O 7 2 (aq) Fe 3+ (aq) + Cr 3+ (aq) oxidation reduction Fe 2+ reductant Cr 2 O 7 2 oxidant NH 3 (aq) + HCl(aq) NH 4 Cl(aq) not a redox reaction

11 Half Reaction Method of Balancing Redox Reactions Assign oxidation states to all atoms Separate reaction into oxidation and reduction half reactions Balance each half reaction by mass Balance elements other than oxygen and hydrogen Balance oxygen with water Balance hydrogen with hydrogen ion Balance each half reaction by charge using electrons Section 18.2 Balancing Oxidation Reduction Equations Multiply each reaction by a factor to make electrons lost and gained equal Add the two reactions together and cancel out electrons and any other species necessary For basic solution add hydroxide ion to each side (enough to fully react with hydrogen ion and form water)

12 Al 3+ (aq) + Cu + (aq) Al(s) + Cu 2+ (aq) Oxidation Half reaction Cu + (aq) Cu 2+ (aq) Cu + (aq) Cu 2+ (aq) + 1 eˉ [ Cu + (aq) Cu 2+ (aq) + 1 eˉ ] x 3 Reduction Half reaction Al 3+ (aq) Al(s) Al 3+ (aq) + 3 eˉ Al(s) Complete balanced reaction Al 3+ (aq) + 3 Cu + (aq) Al(s) + 3 Cu 2+ (aq)

13 Fe 2+ (aq) + Cr 2 O 7 2 (aq) Fe 3+ (aq) + Cr 3+ (aq) Oxidation Half reaction Fe 2+ (aq) Fe 3+ (aq) Fe 2+ (aq) Fe 3+ (aq) + 1 eˉ [ Fe 2+ (aq) Fe 3+ (aq) + 1 eˉ ] x 6 Reduction Half reaction Cr 2 O 7 2 (aq) 2 Cr 3+ (aq) Cr 2 O 7 2 (aq) 2 Cr 3+ (aq) + 7 H 2 O(l) Cr 2 O 7 2 (aq) + 14 H + (aq) 2 Cr 3+ (aq) + 7 H 2 O(l) Cr 2 O 7 2 (aq) + 14 H + (aq) + 6 eˉ 2 Cr 3+ (aq) + 7 H 2 O(l) Complete balanced reaction (in acidic solution) 6 Fe 2+ (aq) + Cr 2 O 7 2 (aq) + 14 H + (aq) 6 Fe 3+ (aq) + 2 Cr 3+ (aq) + 7 H 2 O(l)

14 Fe 2+ (aq) + Cr 2 O 7 2 (aq) Fe 3+ (aq) + Cr 3+ (aq) Complete balanced reaction (in acidic solution) 6 Fe 2+ (aq) + Cr 2 O 7 2 (aq) + 14 H + (aq) 6 Fe 3+ (aq) + 2 Cr 3+ (aq) + 7 H 2 O(l) Complete balanced reaction (in basic solution) 6 Fe 2+ (aq) + Cr 2 O 7 2 (aq) + 14 H + (aq) + 14 OHˉ(aq) 6 Fe 3+ (aq) + 2 Cr 3+ (aq) + 7 H 2 O(l) + 14 OHˉ(aq) 6 Fe 2+ (aq) + Cr 2 O 7 2 (aq) + 14 H 2 O(l) 6 Fe 3+ (aq) + 2 Cr 3+ (aq) + 7 H 2 O(l) + 14 OHˉ(aq) 6 Fe 2+ (aq) + Cr 2 O 7 2 (aq) + 7 H 2 O(l) 6 Fe 3+ (aq) + 2 Cr 3+ (aq) + 14 OHˉ(aq)

15 MnO 4 (aq) + Bi 3+ (aq) Mn 2+ (aq) + BiO 3 (aq) Oxidation Half reaction Bi 3+ (aq) BiO 3 (aq) 3 H 2 O(l) + Bi 3+ (aq) BiO 3 (aq) + 6 H + (aq) + 2 eˉ [ 3 H 2 O(l) + Bi 3+ (aq) BiO 3 (aq) + 6 H + (aq) + 2 eˉ ] x 5 Reduction Half reaction MnO 4 (aq) Mn 2+ (aq) MnO 4 (aq) Mn 2+ (aq) + 4 H 2 O(l) MnO 4 (aq) + 8 H + (aq) Mn 2+ (aq) + 4 H 2 O(l) [ MnO 4 (aq) + 8 H + (aq) + 5 eˉ Mn 2+ (aq) + 4 H 2 O(l) ] x 2 Complete balanced reaction Acidic: 5 Bi 3+ (aq) + 2 MnO 4 (aq) + 7 H 2 O(l) 5 BiO 3 (aq) + 2 Mn 2+ (aq) + 14 H + (aq) + 14 OH (aq) + 14 OH (aq) + 14 H 2 O(l) Basic: 5 Bi 3+ (aq) + 2 MnO 4 (aq) + 14 OH (aq) 5 BiO 3 (aq) + 2 Mn 2+ (aq) + 7 H 2 O(l)

Oxidation I Lose electrons. Reduction I Gain electrons

Oxidation I Lose electrons. Reduction I Gain electrons Oxidation-Reduction (Redox) Reactions In oxidation-reduction (abbreviated as redox ) reactions, electrons are transferred from one reactant to another. Oxidation I Lose electrons Reduction I Gain electrons