Name Period CRHS Academic Chemistry UNIT 10- Reduction/Oxidation Reactions & Electrochemistry NOTES Quiz Date Exam Date Lab Dates Notes, Homework, Exam Reviews and Their KEYS located on CRHS Academic Chemistry Website: https:_ÿ/cincochem.pbworks.corn
Page 2 of 12 Unit 10 Notes 10.1 OXIDATION NUMBERS Oxidation-Reduction " Reactions) - reactions in which Oxidation number- // In the past, we looked at group # on periodic table to find # of valence electrons, then used the octet rule to determine # of electrons lost or gained. Element S Li AI Mg Br # of valence e e lost or gained o oxidation # However, the majority of elements can have (Y/(ÿ%{ÿ, ; ÿ, ÿ i',,' +L numbers (remember the transition metals!) <) oxidation The following oxidation numbers are considered FIXED: All elements in free state have an oxidation number of All diatomic molecules (H2, 02, F2, BF2, 12, N2, CI2) in free state have an oxidation number of Group 1 and 2 metals and aluminum (AI) are always as indicated on the periodic table Oxygen is... ÿ in a compound {except peroxides) > Hydrogen is almost always "ÿ ( in a compound, except when bonded to metal, then <1 Rules: 3 examples with CI el: - t:t:) KCI KCIOÿ More Practice - Assign oxidation numbers to ALL of the elements in each of the compounds or ions below. FeO CuCI2 'AIF H2SO4 H3P03 NO2-
10.2 THE MEANING OF OXIDATION AND REDUCTION Unit 10 Notes Page 3 of 12 Oxidation - --,,)I4 04 ÿ ÿv)ÿ;ÿ?, LEO goes Reduction GER (-_ÿ1 ÿ Ot' '?[('" ' > / /" _'_W_-'r, c.. e /:\ i t.. < All _ÿ')'-ÿ.'i Aÿ, 1" OÿX reactions are paired with a Lÿ.c)'-b{- by the reactant that is ()V'ÿ i;/ÿ! is 'ÿ,<;'ÿittÿa.ÿ ÿ' {-/ÿfiÿ reaction. Electrons that are by the reactant that is f redox reaction: REDOX: Mg + S --> MgS Oxidation Half Reaction:,,' r L t /... ' ÿ, /' k2 Reduction Half Reaction: c <, ", The two reactions above are called 01 i, / Mg,0..ÿ I < e-to become the Mg2+ cation. 2 S fj <ÿ.ÿ j.,ÿ. ÿ-i... e-to become the Sÿ anion. ReducinAaÿent - the reactant that gives up electrons Mg is the reducing agent and is oxidized,(reducing agent is ALWAYS the reactant in oxidation halfreaction) Oxidizing agent - the reactant that gains electrons S is the oxidizing agent and is reduced (oxidizing agent is ALWAYS the reactant in reduction halfreaction)
Page 4 of 12 Unit 10 Notes f'o O Practice 1: 4AI + 302 ---> 2 AI203 Oxidation half-reaction: q/',,("... V Reduction Half Reaction: Reducing Agent: /ÿ1? ( Oxidizing Agent: Practice 2: 4-,, :' #ÿ ['? "4 2AgNOa + Ch --+ Cu(NO3)2 + 2Ag Oxidation: (({b.ÿl, ().(' ÿ';) ( ÿ ÿ'ÿ Reduction' ÿ % ÿ.ÿ ÿ'ÿ, O ÿ,. ÿ/)/i % Reducing Agent:(/ ) Oxidizing Agent: How do I recognize a '!"d t (V'ÿ'z reaction? The i t' NOTE! --> NEVER redox! reactions and reactions are Practice 3: Which of the following reactions represent Redox reactions? /.j, I//1 2KN03 (s) -> 2 KNO2(s) + 02 L//zz H2(g)+ CuO(s)-> Cu(s)+ H20 NaOH (aq) + HCI-> NaCI + H20 /\)0 5. H2(g) + CI2 - > 2 HCl(g) SO3(g) + H20(I) -> H2SO4
Unit 10 Notes Page 5 of 12 20.3 APPLICATIONS OF REDOX REACTIONS The branch of chemistry that deals with electricity related applications of oxidation-reduction reactions is called ÿlÿc:ÿo c'ÿ+,ÿ+ÿ+<:;t ÿ+ÿ. Electrochemical Cell - any device that converts ÿ+,k/ÿ,f?//ÿ? [ energy into ÿ, ÿ r ÿ ÿ" ÿ ÿ or vice versa. Electrochemical cells ÿ 0,!ÿ)'('. 0ÿ, t - + oxidation half reactions from reduction half reactions so that the energy produced or required is electrical energy and not heat. energy Two general types of electrochemical cells: ;ÿ" 10Sil 6 I,ÿ ÿ ÿ' Cells.! [+ iÿ (, Cells and Voltaic or Galvanic Cell - Spontaneously converts (-!/ÿ,,..[ÿ,':4iti,'czÿ i energy into 'ÿ/'!+ energy (using ). Applications - ( 3 ÿ, I (>I++"!,ÿ%+ Basic parts of a voltaic cell 1. 2 ÿjÿ ÿk ÿ'ÿ - C -ÿ I,t % -each has a (t(+'(i(k t I+++ immersed in a 'ÿ++t? ti!jf!iÿ:+iÿ a. b. 2, },,ÿ;ÿ,ÿ ÿ!ÿ +ÿ This is where separate oxidation / reduction reactions take place., -the electrode where [)ÿi ÿ;'ÿ!ÿ!ÿ,i IWI,ÿ takes place (lose e) - the electrode where!ÿ( I( 1ÿ'ÿ! j:,ÿ I 'I takes place (gain e-) - a solution of ions that conducts e- '(;+ ij' +++, ÿ+i(+,+,;ÿ+++ÿ, +/",, ++:+ÿ+ +! ÿ:...,+,,?++i+ +(,., 5
Page 6 of 12 "ÿ> 4. / l'l 'ÿi'/'(ÿ 3. Unit 10 Notes -a pathway constructed to allow ions to pass from one half-cell to another, filled with an electrolyte (i. v,,'{'ÿcÿ', i, metal wire- carries electrons ((i.(,) ((.fÿ tÿ )from ÿ F) O(!' to (d4.tÿt()(ÿ'ÿ:' Example: zinc-copper voltaic cell Zn + Cu2+ > Zn2+ + Cu Two half-reactions for redox: Oxidation: 2ÿ.//r, :2> "2 Vÿ 'ÿ'( / ;?C" Reduction { ÿ) ÿ' ÿ f 2(ÿ 'ÿp(ÿ)-ÿ ÿ ''ÿ,t!,ÿ,, -ÿ "ÿ, Anode(... ql(t V' ÿd//'lo l )where ÿg,/cÿ<{/r)ÿi takes place is anode (1 h.ÿ, ',, <'ÿ ;ÿd,ltÿ ',,,, piece of ÿy,, /{ÿ'. {,q t atoms of ÿ2_v,,,,>,i Vvt(' 0, l J : 2,... is immersed in '2 ÿ 2,,},,,ÿ shorthand for this half-cell reaction is Z.vi ÿ ÿ" ÿ', :;ÿ' singl"el " ts Cathode (!ÿ(i'iÿ'ÿ'ÿ'vli, )where!2ÿ 'il ÿ, ÿ' ÿ ÿ,"/ e (a) is cathode (Gÿvÿ,"? b" ÿ,ÿ't, piece of () is immersed in atoms of o shorthand for this half-cell reaction is d,\ takes plac ÿt'7i:/! i:ii Electric Cell Potential How do we measure how "strong" an electrochemical cell is? Electric potential, Ece,- a measure of the cell's ability to i)ÿ' OC!ÿ ÿi,ÿ? Units are \[ÿ) t, ÿ oÿ,!ÿ ÿ7" Use table of relative Standard Reductions Potentials on Page 9 to calculate E cell, where E cell = E0red - E0oxid
Unit 10 Notes Page 7 of 12 Standard aedunon Potontials at 25% (298 K) for Many Common Half-reactions Half-reaction "ÿ; (V) F[alf-reacdon Fz + 2e- --+ 2F- 2.87 Ag2++ e- ÿ Ag+ 1.99 Coÿ+ + e- -+ Co2+ 1.82 H202 q- 2bt+ + 2e- -+ 21420 1.78 Ce4+ + e= --+ Ceÿ'+ 1.70 PbO2 + 4H+ + SO42- q- 2e- -+ PbSO4 + 2H20 1.69 MnO4- + 4H+ +.?,e- ---+." MnO2 + 2H20 1.68 IO4- + 2H + 2e- ÿ IQ- + HzO 1,60 MnO4- + 8H+ + 5e- -+ Mna+ + 4H20 1,51 Atrÿ+ + 3e- -+: Au!ÿ50 PbOz+4H++ 2e- -+. Pb2++2H20 1.46 CIa + 2e- -+' 2C.I- 1.36 Cv2072- -4-14H+ + 6e- --+ 2C:rÿ+ + 7[420 1.33 {92 + 4H+ + 4e- ÿ 2H20 1.23 MnO2 + 4H+ + 2e- + NIl12+ + 2H20 1ÿ21 1 10ÿ- +6H+ + 5e- -+ ÿ}12-f ÿh2{) 1,20 Br, + 2e- --> 2gr- 1.09 VO2+ + 214+ + e= + VOz+ +I=120 1.0(} AuCI4- + 3e- + Au + 4C1-0.99 NOÿ,- + 4H + 3e- ÿ NC} + 2H20 0,96 C[O2 + e- --ÿ,, C]Oÿ- (I.ÿJ54 2Hgz+ + 2e- ÿ H:d22+ 0.91 Ag+ +,.'- ÿ A'g 0.80 14922 + 2c- -ÿ-!hg (I,:ÿ(I Fe;ÿ+ + e- -+ FX'2+ 0.77 O2 + 2H+ + 2e- -+ H2()2 (1.68 N'[I104-q-,:- -+ i\411(}42-0,56 lz + 2e- -+ 2I- 0.54 Cu+ + e= ---> Cu 0.52 AgCI + e- ---+ Ag + CI= SO42- q- 4H+ + 2e- -+ 14ÿSOÿ. + Iq20 Cu2++ e- ---+ Cu+ 2H+ + 2e- --+: [42 Fe'ÿ+ + 3e- -+' Fe Pb2+ + 2e- ---+ Pb Sn2+ + 2e- --+ Sn Ni2+ + 2e- -+. Ni PbSO4 + 2eÿ -+ Pb + S(])42- Cd2+ + 2e- -+ Cd Fe2 + 2e- ---+ Fe CI'ÿ+ + e- --> El'2+ "2T ; + 2ow M112+ + 2e- ÿ MI1 AIÿ+ + 3e- ÿ AI H2+2e- + 2H- Mg2+ + 2e ÿ Mg [.aÿ* + 3e- ÿ [;/ Na + -kc- --<. Na Ca1+ + 2e- --> Ca Baÿ+ + 2e- --+ Ba K++e- --> K [,i++e- -+ Li 0,40 0.27 0,22 0.20 0,16 0.00-0,036-0.13-0.14-0.23-0.35-0.40-0.44-0.50-0..73 "= 0.76..,,,ÿ - l,lÿ -[ÿ66-2.271 -o.2.ÿ7-2..37 --2.71-2.76-2.90-2ÿ92-3.05 Example: Calculate standard cell potential, E cell, for the Zn-Cu electrochemical cell: E red(cu+2+2e-1--+cu) minus -- 8, / E oxid (Zn --> Zn+2 + 2e-1) equals l, E cell, then reaction is,spo< )q ous I, then reaction is NOTE: Do not multiply Standard Reduction Potentials by coefficients of balanced redox reactions. 7
Page 8 of 12 Unit 10 Notes Example: Ni + Mg2+ _> Mg + Ni2+ a) Write the 2 half reactions and label as oxidation or reduction... 0,:,'ÿ; ti b) c) Calculate E cell Is this,v(?eaction spontaneous?... - " ' Practice 1: 2 Ag + Fe 2+ ÿ 2 Ag + + Fe a) Write the 2 half reactions and label as oxidation or reduction -.los,..... C)ÿ7</ Is this redox reaction spontaneous?.,:... 1,1';< \ l<fÿ " i.,,..o,+,j.+,(ÿ ÿ ;'"ÿ<ioo lÿj;' U \, 1 Practice 2: Given a voltaic cell constructed using the foiiowing half-reactions Cu2+ + 2 e- ----> Cu AI3+ + 3 e- ----> AI E cu = +0.34 V E AI = -1,66 V a) b) c) Calculate E cell :I:' i::ÿ(l " Is this redox reaction spontaneous? What metal will anode??// >, What metal will be cathode?
Unit 10 Notes Page 9 of 12 Electrolytic Cells If electrical energy is required to produce a redox reaction and bring about a chemical change in an electrochemical cell, it is an <ÿ tÿ (ÿ ÿd ÿ ÿ c ÿj cell. The redox reaction in an electrolytic cell is ÿ:)at'ÿ,' i (7 71 ÿ,(ÿ)<ÿ,of the voltaic cell, and is essentially the Voltaic/Galvanic Cell vs Electrolytic Cell 0,74 V power supply voltmeter Cd anode, (+) i Cu cathode Cd cathode (+) Cu, anode 1 MCd21 //' 1 M CLI2t ] M CU2t anode: cathode; cathode: anode; Cd(s) ÿ Cd2+(acl) + 2e- Cu2*(aq) + 2e -> Cu(s) Cd2+(aq) + 2e---ÿ Cd(s) Cu(s) ÿ Cu2*(aq) + 2e Overall reaction: Cd(s) + Cu2ÿ(aq) -ÿ Cd2+(aq) + Cu(s) (a) Galvanic cell Overall reaction: Cd2+(aq) + Cu(s) -ÿ Cd(s) + Cu2+(aq) (b) Electrolytic coll Applications fl)r each include /
Page 10 of 12 Unit 10 Notes
Unit 10 Notes Page 11 of 12 Common Polyatomic Ions List Name Ion acetate C2H3OZ or CH3COO- hypochlorite CIOammonium NH4 nitrate NO3- carbonate CO32- nitrite NO2- chlorate CIO3- perchlorate CIO4- chlorite CIO2- permanganate MnO4- chromate CrO42- phosphate PO43- cyanide CN- phosphite PO33- dichromate Cr2072- silicate SiO32- hydrogen carbonate HCO3- sulfate SO42- hydroxide OH- sulfite SO32- i = I 2 = II 3 =III 4 = IV 5 = V 6 = VI Metal Lltlflum Poÿabslum Barkml Caldum Sod ILlm Nagneslum Alurnlnu m Hanganese Zinc Chromium Iron Cobalt Nickel Tin Lead (Hydrogen) Copper MeFcury Silver Platinum Gold 11
Page 12 of 12 Unit 10 Notes, ÿ ÿ ÿ:ÿ ÿ ÿ+g: +o ÿ0 ÿ+ ÿgÿ ÿ ÿ oÿ fi cÿ L) E cÿ O CD CO +ÿ "+ m +++,- i +i O q' 1:2,.++ ++++.+ n2 - I?X.+,t) rd % '? 0"1 'ÿ2 N r,9 5 _1 <D ÿ11 69 2 O.J CO "++Jr LO ÿ2ÿ r", r- rÿ +0 '+d J +++J