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CHM 112
Section 1

Homework Assignment #29
Due April 24, 2006 by 8:05 a.m.

Practice (not to be turned in): Practice reactions 51 - 70, 18.26, 18.27, 18.28, 18.29, 18.30, 18.31, 18.87

Part 1

Complete and balance the reactions corresponding to the last digit of your Student ID Number. Then calculate the standard potential for the reaction.

0) Zn(s) + Ni(OH)3(s) Ni(OH)2(s) + [Zn(OH)4]2–(aq)

1) Al(s) + BrO(aq) [Al(OH)4](aq) + Br2(l)

2) Mg(s) + SO32–(aq) Mg(OH)2(s) + S(s)

3) [Cr(OH)4](aq) + NO3(aq) CrO42–(aq) + NO2(aq)

4) Co(OH)2(s) + ClO3(aq) ClO2(aq) + Co(OH)3(s)

5) Al(s) + MnO4(aq) MnO2(s) + [Al(OH)4](aq)

6) Co(OH)2(s) + HO2(aq) Co(OH)3(s)

7) Zn(s) + MnO4(aq) MnO2(s) + [Zn(OH)4]2–(aq)

8) [Cr(OH)4](aq) + OCl(aq) CrO42–(aq) + Cl(aq)

9) [Al(OH)4](aq) + Mg(s) Al(s) + Mg(OH)2(s)

Part 2

Complete and balance the reaction corresponding to the sixth digit of your Student ID number.

0) Fe(NO3)2(aq) + K2CO3(aq)

1) Co(NO3)2(aq) + K3PO4(aq)

2) Mn(NO3)2(aq) + K2CO3(aq)

3) Fe(NO3)3(aq) + K3PO4(aq)

4) Co(NO3)3(aq) + K2CO3(aq)

5) Fe(NO3)2(aq) + K3PO4(aq)

6) Co(NO3)2(aq) + K2CO3(aq)

7) Mn(NO3)2(aq) + K3PO4(aq)

8) Fe(NO3)3(aq) + K2CO3(aq)

9) Co(NO3)3(aq) + K3PO4(aq)



Answers:

Part 1

All of these reactions are done in base. To find the standard potential, each half–reaction must be balanced in base.

0) Zn(s) + Ni(OH)3(s) Ni(OH)2(s) + [Zn(OH)4]2–(aq)

Zn(s) + 4 OH(aq) [Zn(OH)4]2–(aq) + 2 e      Eoox = +1.285 V


[ Ni(OH)3(s) + e Ni(OH)2(s) + OH(aq) ] × 2      Eored = +0.48 V

(These two half–reactions are easily balanced in base by inspection.)


Net: Zn(s) + 2 Ni(OH)3(s) + 2 OH(aq) 2 Ni(OH)2(s) + [Zn(OH)4]2–(aq)

Eo = +1.285 + 0.48 = +1.77 V


1) Al(s) + BrO(aq) [Al(OH)4](aq) + Br2(l)

[ Al(s) + 4 OH(aq) [Al(OH)4](aq) + 3 e ] × 2      Eoox = +2.310 V

(This half–reaction is easily balanced in base by inspection.)


In acid: 2 BrO(aq) + 4 H+(aq) + 2 e Br2(l) + 2 H2O(l)

Neutralization: 4 H2O(l) 4 H+(aq) + 4 OH(aq)

In base: [ 2 BrO(aq) + 2 H2O(l) + 2 e Br2(l) + 4 OH(aq) ] × 3      Eored = +0.455 V


Net: 2 Al(s) + 6 BrO(aq) + 6 H2O(l) 2 [Al(OH)4](aq) + 3 Br2(l) + 4 OH(aq)

Eo = +2.310 + 0.455 = +2.765 V


2) Mg(s) + SO32–(aq) Mg(OH)2(s) + S(s)

[ Mg(s) + 2 OH(aq) Mg(OH)2(s) + 2 e ] × 2      Eoox = +2.687 V

(This half–reaction is easily balanced in base by inspection.)


In acid: SO32–(aq) + 6 H+(aq) + 4 e S(s) + 3 H2O(l)

Neutralization: 6 H2O(l) 6 H+(aq) + 6 OH(aq)

In base: SO32–(aq) + 3 H2O(l) + 4 e S(s) + 6 OH(aq)      Eored = –0.66 V


Net: 2 Mg(s) + SO32–(aq) + 3 H2O(l) 2 Mg(OH)2(s) + S(s) + 2 OH(aq)

Eo = +2.687 – 0.66 = +2.03 V


3) [Cr(OH)4](aq) + NO3(aq) CrO42–(aq) + NO2(aq)

In acid: [Cr(OH)4](aq) CrO42–(aq) + 4 H+(aq) + 3 e

Neutralization: 4 H+(aq) + 4 OH(aq) 4 H2O(l)

In base: [ [Cr(OH)4](aq) + 4 OH(aq) CrO42–(aq) + 4 H2O(l) + 3 e ] × 2      Eoox = +0.13 V


In acid: NO3(aq) + 2 H+(aq) + 2 e NO2(aq) + H2O(l)

Neutralization: 2 H2O(l) 2 H+(aq) + 2 OH(aq)

In base: [ NO3(aq) + H2O(l) + 2 e NO2(aq) + 2 OH(aq) ] × 3      Eored = +0.01 V


Net: 2 [Cr(OH)4](aq) + 3 NO3(aq) + 2 OH(aq) 2 CrO42–(aq) + 3 NO2(aq) + 5 H2O(l)

Eo = +0.13 + 0.01 = +0.14 V


4) Co(OH)2(s) + ClO3(aq) ClO2(aq) + Co(OH)3(s)

[ Co(OH)2(s) + OH(aq) Co(OH)3(s) + e ] × 2      Eoox = –0.17 V

(This half–reaction is easily balanced in base by inspection.)


In acid: ClO3(aq) + 2 H+(aq) + 2 e ClO2(aq) + H2O(l)

Neutralization: 2 H2O(l) 2 H+(aq) + 2 OH(aq)

In base: ClO3(aq) + H2O(l) + 2 e ClO2(aq) + 2 OH(aq)      Eored = +0.35 V


Net: 2 Co(OH)2(s) + ClO3(aq) + H2O(l) ClO2(aq) + 2 Co(OH)3(s)

Eo = –0.17 + 0.35 = +0.18 V


5) Al(s) + MnO4(aq) MnO2(s) + [Al(OH)4](aq)

Al(s) + 4 OH(aq) [Al(OH)4](aq) + 3 e      Eoox = +2.310 V

(This half–reaction is easily balanced in base by inspection.)


In acid: MnO4(aq) + 4 H+(aq) + 3 e MnO2(s) + 2 H2O(l)

Neutralization: 4 H2O(l) 4 H+(aq) + 4 OH(aq)

In base: MnO4(aq) + 2 H2O(l) + 3 e MnO2(s) + 4 OH(aq)      Eored = +0.60 V


Net: Al(s) + MnO4(aq) + 2 H2O(l) MnO2(s) + Al(OH)4(aq)

Eo = +2.310 + 0.60 = +2.91 V


6) Co(OH)2(s) + HO2(aq) Co(OH)3(s)

[ Co(OH)2(s) + OH(aq) Co(OH)3(s) + e ] × 2      Eoox = –0.17 V

(This half–reaction is easily balanced in base by inspection.)


In acid: HO2(aq) + 3 H+(aq) + 2 e 2 H2O(l)

Neutralization: 3 H2O(l) 3 H+(aq) + 3 OH(aq)

In base: HO2(aq) + H2O(l) + 2 e 3 OH(aq)     Eored = +0.88 V


net: 2 Co(OH)2(s) + HO2(aq) + H2O(l) 2 Co(OH)3(s) + OH(aq)

Eo = +0.17 + 0.88 = +1.05 V


7) Zn(s) + MnO4(aq) MnO2(s) + [Zn(OH)4]2–(aq)

[ Zn(s) + 4 OH(aq) [Zn(OH)4]2–(aq) + 2 e ] × 3      Eoox = +1.285 V

(This half–reaction is easily balanced in base by inspection.)


In acid: MnO4(aq) + 4 H+(aq) + 3 e MnO2(s) + 2 H2O(l)

Neutralization: 4 H2O(l) 4 H+(aq) + 4 OH(aq)

In base: [ MnO4(aq) + 2 H2O(l) + 3 e MnO2(s) + 4 OH(aq) ] × 2      Eored = +0.60 V


Net: 3 Zn(s) + 2 MnO4(aq) + 4 OH(aq) + 4 H2O(l) 2 MnO2(s) + 3 [Zn(OH)4]2–(aq)

Eo = +1.288 + 0.60 = +1.89 V


8) [Cr(OH)4](aq) + OCl(aq) CrO42–(aq) + Cl(aq)

In acid: [Cr(OH)4](aq) CrO42–(aq) + 4 H+(aq) + 3 e

Neutralization: 4 H+(aq) + 4 OH(aq) 4 H2O(l)

In base: [ [Cr(OH)4](aq) + 4 OH(aq) CrO42–(aq) + 4 H2O(l) + 3 e ] × 2      Eoox = +0.13 V


In acid: OCl(aq) + 2 H+(aq) + 2 e Cl(aq) + H2O(l)

Neutralization: 2 H2O(l) 2 H+(aq) + 2 OH(aq)

In base: [ OCl(aq) + H2O(l) + 2 e Cl(aq) + 2 OH(aq) ] × 3      Eored = +0.890 V


Net: 2 [Cr(OH)4](aq) + 3 OCl(aq) + 2 OH(aq) 2 CrO42–(aq) + 3 Cl(aq) + 5 H2O(l)

Eo = +0.13 + 0.890 = +1.02 V


9) [Al(OH)4](aq) + Mg(s) Al(s) + Mg(OH)2(s)

[ [Al(OH)4](aq) + 3 e Al(s) + 4 OH(aq) ] × 2      Eored = –2.310 V

(This half–reaction is easily balanced in base by inspection.)


[ Mg(s) + 2 OH(aq) Mg(OH)2(s) + 2 e ] × 3      Eoox = +2.687 V

(This half–reaction is easily balanced in base by inspection.)


Net: 2 [Al(OH)4](aq) + 3 Mg(s) 2 Al(s) + 3 Mg(OH)2(s) + 2 OH(aq)

Eo = +2.687 – 2.310 = +0.377 V



Part 2

These are all precipitation reactions.

0) Fe(NO3)2(aq) + K2CO3(aq)

Fe(NO3)2(aq) + K2CO3(aq) FeCO3(s) + 2 K+(aq) + 2 NO3(aq)

1) Co(NO3)2(aq) + K3PO4(aq)

3 Co(NO3)2(aq) + 2 K3PO4(aq) Co3(PO4)2(s) + 6 K+(aq) + 6 NO3(aq)

2) Mn(NO3)2(aq) + K2CO3(aq)

Mn(NO3)2(aq) + K2CO3(aq) MnCO3(s) + 2 K+(aq) + 2 NO3(aq)

3) Fe(NO3)3(aq) + K3PO4(aq)

Fe(NO3)3(aq) + K3PO4(aq) FePO4(s) + 3 K+(aq) + 3 NO3(aq)

4) Co(NO3)3(aq) + K2CO3(aq)

2 Co(NO3)3(aq) + 3 K2CO3(aq) Co2(CO3)3(s) + 6 K+(aq) + 6 NO3(aq)

5) Fe(NO3)2(aq) + K3PO4(aq)

3 Fe(NO3)2(aq) + 2 K3PO4(aq) Fe3(PO4)2(s) + 6 K+(aq) + 6 NO3(aq)

6) Co(NO3)2(aq) + K2CO3(aq)

Co(NO3)2(aq) + K2CO3(aq) CoCO3(s) + 2 K+(aq) + 2 NO3(aq)

7) Mn(NO3)2(aq) + K3PO4(aq)

3 Mn(NO3)2(aq) + 2 K3PO4(aq) Mn3(PO4)2(s) + 6 K+(aq) + 6 NO3(aq)

8) Fe(NO3)3(aq) + K2CO3(aq)

2 Fe(NO3)3(aq) + 3 K2CO3(aq) Fe2(CO3)3(s) + 6 K+(aq) + 6 NO3(aq)

9) Co(NO3)3(aq) + K3PO4(aq)

Co(NO3)3(aq) + K3PO4(aq) CoPO4(s) + 3 K+(aq) + 3 NO3(aq)