1. Oxidation-Reduction Reactions Ch. 16

2. What is Oxidation? Oxygen is most abundant element on Earth Extremely reactive due to strong electronegativity Oxidation is a reaction with Oxygen Element loses electrons becoming more positively charged Iron Nail Fe 2 O 3 (rust) Oxidation 4Fe + 3O 2 --> Fe 2 O 3 Fe  Fe +3 ; Iron loses 3 electrons

3. What is Reduction? In an oxidation reaction, there is also a reduction of an element Element gains more electrons becoming more negatively charged Watch the oxidation numbers! Iron Nail Fe 2 O 3 (rust) Oxidation 4Fe + 3O 2 --> 2Fe 2 O 3 O 2  O 2- ; Oxygen takes 2 electrons Reduction

4. Oxidation Numbers Oxidation number tells you how many electrons an element has gained/lost compared to it natural state Fe  natural state (no charge); 0 Fe +2  oxidized state; +2 Fe +3  even more oxidized state; +3 O -2  Cl -  Na +  Oxidation increase the oxidized state Reductions decrease the oxidized state NF 3  -2+1 F  F -  -1 Compound has net charge of 0; 0= x + ((-1)x3)= +3 N= +3

5. Oxidation Number Rules 1)One element present; charge is 0 2)Monoatomic ions have normal charge; Cl - = -1 3)All Group 1A metals have a charge of +1 4)All Group 2A metals have a charge of +2 5)Hydrogen is +1 when bonded to a nonmetal; Hydrogen is -1 when bonded to a metal 6)Oxygen is -1 when in a peroxide (H 2 O 2 ); Oxygen is -2 in all other compounds 7)Fluorine is always -1 8)The sum of oxidation numbers must equal 0 is a neutral compound 9)The sum of oxidation numbers must equal the charge of the polyatomic ion the elements create

6. Calculating Oxidation Number What are oxidation numbers of the elements in: Na 2 SO 4 Na= +1O= -2compound is neutral 0= (+1)2 + X + (-2)4 X= +6; S= +6 K 2 Cr 2 O 7 : K= +1O=-2compound is neutral 0= (+1)2 + 2(X) + (-2)7 X= +6; Cr= +6

7. Oxidation Number Practice 1)Ba(NO 3 ) 2  2) (NH 4 ) 2 SO 4  3) PO 4 3-  4) Cr 2 O 7 2-  5) HClO 2  Ba= +2, O= -2, N= +5 H=+1, O=-2, N= -3, S= +6 O=-2; P= +5 O= -2, Cr= +6 H= +1, O=-2, Cl= +3

8. Oxidation-Reduction Reactions Redox reactions- a chemical reaction with the transfer of electrons Rusting, combustion rxn, photography, smelting, biochemistry… Have two “Half-Reactions”; one oxidation and one reduction 2 Zn +O 2  2 ZnO 1) 2 Zn  2 Zn 2+ + 4 e - 2) O 2 + 4 e -  2 O 2- Oxidized Reduced

9. Redox Reactions OIL RIG…. Oxidized If Loses Is this a redox reaction? What is reduced/oxidized? Mg + 2 HCl  MgCl 2 + H 2 Mg: 0  +2; Loses e -, oxidized H: +1  0; Gains e -, reduced ?????? Reduced If Gaines 0 0 +2 +1 Chlorine is unaffected

10. Practice Are the following redox reactions? What is oxidized? What is reduced? 1)Ag + H 2 S + O 2  Ag 2 S + H 2 O 2) HCl + NaOH  NaCl + H 2 O 3) C 6 H 12 O 6 + O 2  CO 2 + H 2 O 4) NaOH + Cl 2  NaCl + NaClO + H 2 O Remember OIL RIG Ag: 0  +1; Oxidized O: 0  -2; Reduced H: +1  +1 H: +1  +1 Cl: -1  -1 Na: +1  +1 O: -2  -2 H: +1  +1 C: 0  +4; Oxidized O: -2  -2; 0  -2; Reduced Na: +1  +1 H: +1  +1 O:-2  -2 Cl: 0  -1; Reduced 0  +1; Oxidized

11. Oxidizing/Reducing Agents Oxidizing agents are the substances that gain electrons in a redox reaction Oxidizing agents are reduced materials Reducing agents are the substances that lose electrons in a redox reaction Reducing agents are oxidized materials CuSO 4 + Zn  ZnSO 4 + Cu Cu 2+ + 2e -  Cu Zn  Zn 2+ + 2e - Copper (II) sulfate Zinc Copper Reduced material Oxidizing agent Oxidized material Reducing agent

12. Practice For the following label the oxidizing/reducing agents 1)H 2 + F 2 → 2 HF 2)Cr 2 O 3 + Al ----> Cr + Al 2 O 3 3)4 Al + 2O 2  2Al 2 O 3 H: 0  +1; Oxidized, reducing agent F: 0  -1; Reduced, oxidizing agent Al: 0  +3; Oxidized, reducing agent Cr: +3  0; Reduced, oxidizing agent O: 0  -2; Reduced, oxidizing agent Al: 0  +3; Oxidized, reducing agent

13. Homework 1)Ch. 16 workbook 2)Group Presentations: -Groups will present on one of the redox topics from 16.2 -Groups must use a PPT, pictures, videos, etc… -In your presentation you must explain: -All vocabulary used -Chemical reactions occurring -Examples of the redox reaction All group members must speak! Presentation time between 5-10 minutes long!! Bring all PPTs to me Tuesday morning to make sure they work on my laptop!!!