Oxidation-Reduction Reactions

Oxidation-Reduction ReactionsCh. 16

What is Oxidation?Oxygen is most abundant element on EarthExtremely reactive due to strong electronegativityOxidation is a reaction with OxygenElement loses electrons becoming more positively charged

Iron NailFe2O3(rust)Oxidation4Fe + 3O2 --> Fe2O3FeFe+3; Iron loses 3 electrons

What is Reduction?In an oxidation reaction, there is also a reduction of an elementElement gains more electrons becoming more negatively chargedWatch the oxidation numbers!

Iron NailFe2O3(rust)Oxidation4Fe + 3O2 --> 2Fe2O3O2O2-; Oxygen takes 2 electronsReduction

Oxidation NumbersOxidation number tells you how many electrons an element has gained/lost compared to it natural stateFe natural state (no charge); 0Fe+2 oxidized state; +2Fe+3 even more oxidized state; +3O-2 Cl- Na+ Oxidation increase the oxidized stateReductions decrease the oxidized stateNF3 -2-1+1F F- -1Compound has net charge of 0; 0= x + ((-1)x3)= +3N= +3

Oxidation Number RulesOne element present; charge is 0Monoatomic ions have normal charge; Cl- = -1All Group 1A metals have a charge of +1All Group 2A metals have a charge of +2Hydrogen is +1 when bonded to a nonmetal; Hydrogen is -1 when bonded to a metalOxygen is -1 when in a peroxide (H2O2); Oxygen is -2 in all other compoundsFluorine is always -1The sum of oxidation numbers must equal 0 is a neutral compoundThe sum of oxidation numbers must equal the charge of the polyatomic ion the elements create

Calculating Oxidation NumberWhat are oxidation numbers of the elements in:Na2SO4Na= +1O= -2compound is neutral0= (+1)2 + X + (-2)4X= +6; S= +6K2Cr2O7:K= +1O=-2compound is neutral0= (+1)2 + 2(X) + (-2)7X= +6; Cr= +6

Oxidation Number PracticeBa(NO3)2

2) (NH4)2SO4

3) PO43-

4) Cr2O72-

5) HClO2

Ba= +2, O= -2, N= +5H=+1, O=-2, N= -3, S= +6 O=-2; P= +5O= -2, Cr= +6H= +1, O=-2, Cl= +3

Oxidation-Reduction ReactionsRedox reactions- a chemical reaction with the transfer of electronsRusting, combustion rxn, photography, smelting, biochemistryHave two Half-Reactions; one oxidation and one reduction

2 Zn +O2 2 ZnO1) 2 Zn 2 Zn2+ + 4 e-2) O2 + 4 e- 2 O2-

Oxidized Reduced

Redox ReactionsOIL RIG.Oxidized If LosesIs this a redox reaction?What is reduced/oxidized? Mg + 2 HCl MgCl2 + H2

Mg: 0+2; Loses e-, oxidizedH: +1 0; Gains e-, reduced

??????Reduced IfGaines00-1+2-1+1Chlorine is unaffected

PracticeAre the following redox reactions?What is oxidized? What is reduced?Ag + H2S + O2 Ag2S + H2O

2) HCl + NaOH NaCl + H2O

3) C6H12O6 + O2 CO2 + H2O

4) NaOH + Cl2 NaCl + NaClO + H2O Remember OIL RIGAg: 0+1; Oxidized O: 0-2; Reduced H: +1 +1H: +1+1 Cl: -1 -1 Na: +1 +1 O: -2 -2H: +1 +1 C: 0+4; Oxidized O: -2 -2; 0-2; ReducedNa: +1+1 H: +1+1 O:-2 -2 Cl: 0-1; Reduced 0+1; Oxidized

Oxidizing/Reducing AgentsOxidizing agents are the substances that gain electrons in a redox reactionOxidizing agents are reduced materialsReducing agents are the substances that lose electrons in a redox reactionReducing agents are oxidized materials

CuSO4 + Zn ZnSO4 + Cu Cu2+ + 2e- Cu Zn Zn2+ + 2e-

Copper (II) sulfateZincCopperReduced materialOxidizing agentOxidized materialReducing agent11

PracticeFor the following label the oxidizing/reducing agentsH2+ F2 2 HF

Cr2O3+ Al----> Cr+ Al2O3

4 Al + 2O2 2Al2O3

H: 0 +1; Oxidized, reducing agent F: 0 -1; Reduced, oxidizing agentAl: 0+3; Oxidized, reducing agentCr: +30; Reduced, oxidizing agent O: 0 -2; Reduced, oxidizing agent Al: 0 +3; Oxidized, reducing agent

HomeworkCh. 16 workbookGroup Presentations:Groups will present on one of the redox topics from 16.2Groups must use a PPT, pictures, videos, etcIn your presentation you must explain:All vocabulary usedChemical reactions occurringExamples 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!!!