Solutions_to_Petrucci_Chapter_20 - Chapter20...

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Chapter 20: Electrochemistry (b) Oxidation: {MgG)- Mg'* (aq)+z e- } x3 Reduction: {Sc3* (aq)+3 e + Sc (s) | x2 - E" = +2.356 Y E"{ Sc3*/Sc } Net: 3 tntg G)* 2 Sc3* (uq) -+ 3 Mg2. (aq)+2 Sc (s) Eo{Sc3* /Sc} = +0.33 V -2.356 V = -2.03 V Ei"u = +0'33 V - E" lcuz*/cu* 1 Eo =+0.800V V V Ll. (a) Oxidation: Sn (r) - Sn2* (aq)+ 2e- Reduction: Pbz* (aq)+ze- + Pb(s) - 8" - +O.l37 V Eo=-0.125 V Net: Sn (r)*Pb2* (uq) -+ Sn2* (uq)*PbG) (b) Oxidation: 2r- (uq) 1rr(s)+ 2e- Reduction: Cu2* (aq)+2e- + Cu (s) Elu = +0'012V - Eo = -0.535 V Eo =+O.340V Spontaneous (c) Oxidation: Cu* (uq ) -) Cu2* (aq )+e Reduction: Ag* (uq)*- -+ Ag (s) Net: Cu* (aq)+Ag. (uq)-> Cu2* (aq)+ng(s) Elu = {.641 V -Eo{Cu2*/Cu*} = +0.641 V -0.800 V- -0.159 V E"{Cuz*lCu*} = +0.159 V Predicting Oxidation-Reduction Reactions 9. The pertinent reactions are shown below. 3 Na (s)+ Al3* (uq) * 3 Na* (uq)* Al (s) ; EJ"rr = - (-2.7 r3V)* (-t.0t 0V) = +r .037 2 Na (r) * HzoQ) + 2 Na+ (uq)* H, (g)+ zoIJ- (uq) ; E&,, - -(-2.713 V)+ (-0.828 V)= +1.885 Both reactions are spontaneous under standard conditions. However, the reduction of water has a more favorable cell potential when compared to the reduction of aluminum metal. The only half reactions that occurs is this system is the reduction of water and the oxidation of sodium metal. 10. The reaction that occurs is Zn(s) -+ Zn2*(uq) + 2e- . Some of the electrons produced in this reaction move to the copper surface, where the following reduction occurs. 2 H.(aq) +2e- 1Hr(g). fhe copper does not react with the HCI(aq) even under these circumstances. Bubbles of hydrogen form more readily on the copper surface than they do on azinc metal surface. We say that the copper surface has a lower overpotential. Not as high a voltage is required to produce Hr(g) because of the iurangement of atoms on the copper surface. Net: 2I- (uq) + Cu2* (uq)--+ Cu(r) * I, (r) 773 E"lr= - 0. 195 V Nonspontaneous
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Chapter 20: Electrochemistry Oxidation: {2H2O(l) -+ O, (g)*aH. (aq) +4e' } x3 Reduction: {NOr-(aq)+aH. (aq)+3e- -+ NO (g)+zHro(l)} x4 (c) -8"--l .229V Eo = +0.956 V Net: 4Nor- (uq) + 4H* (uq) -+ 3Or(g) * 4No(e) * 2HrO(l) This reaction is not spontaneous under standard conditions. (d) oxidation: Cl- (^q) + zal/'- (uq) + oCl- (uq) + Hro(l) + 2e- Reduction: o, (g) * Hro(l) + 2 e- + O, (g) * zOH- (uq) Elo= -0'273 V -Eo=-0.890V Eo = +1.246 Y Net: Cl- (uq) * O, (e) - OCI- (uq) + O, (gXbasic solution) Elu = +0.356V This reaction is spontaneous under standard conditions. 12. It is more difficult to oxidize Hg(l) to Hgr2* (-O.lOl V) than it is to reduce ff to H2 (0.000 V); Hg(l) will not dissolve in 1 M HCl. The standard reduction of nitrate ion to NO(g) in acidic solution is strongly spontaneous in acidic media ( +0.956 V ). This can help overcome
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Solutions_to_Petrucci_Chapter_20 - Chapter20...

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