Balance each of the following redox reactions occurring in basic solution. Part

Question

Balance each of the following redox reactions occurring in basic solution.

Part A

MnO?4(aq)+Br?(aq)?MnO2(s)+BrO?3(aq)

choose correct

MnO?4(aq)+H2O(l)+2Br?(aq)?MnO2(s)+OH?(aq)+2BrO?3(aq)

Part B

Ag(s)+CN?(aq)+O2(g)?Ag(CN)?2(aq)

choose correct

4Ag(s)+8CN?(aq)+O2+2H2O(l)(g)?4Ag(CN)?2(aq)+4OH?(aq)

Part C

NO?2(aq)+Al(s)?NH3(g)+AlO?2(aq)

choose correct

MnO?4(aq)+H2O(l)+Br?(aq)?MnO2(s)+2OH?(aq)+BrO?3(aq) 2MnO?4(aq)+H2O(l)+Br?(aq)?2MnO2(s)+2OH?(aq)+BrO?3(aq) 2MnO?4(aq)+H2O(l)+Br?(aq)?2MnO2(s)+OH?(aq)+BrO?3(aq)

MnO?4(aq)+H2O(l)+2Br?(aq)?MnO2(s)+OH?(aq)+2BrO?3(aq)

Part B

Ag(s)+CN?(aq)+O2(g)?Ag(CN)?2(aq)

choose correct

2Ag(s)+4CN?(aq)+2O2+H2O(l)(g)?2Ag(CN)?2(aq)+2OH?(aq) 2Ag(s)+8CN?(aq)+4O2+2H2O(l)(g)?4Ag(CN)?2(aq)+8OH?(aq) 4Ag(s)+2CN?(aq)+O2+4H2O(l)(g)?4Ag(CN)?2(aq)+8OH?(aq)

4Ag(s)+8CN?(aq)+O2+2H2O(l)(g)?4Ag(CN)?2(aq)+4OH?(aq)

Part C

NO?2(aq)+Al(s)?NH3(g)+AlO?2(aq)

choose correct

NO?2(aq)+H2O(l)+2Al(s)+OH?(aq)?NH3(g)+2AlO?2(aq) 2NO?2(aq)+H2O(l)+2Al(s)+OH?(aq)?2NH3(g)+2AlO?2(aq) 2NO?2(aq)+H2O(l)+Al(s)+2OH?(aq)?2NH3(g)+AlO?2(aq) NO?2(aq)+2H2O(l)+Al(s)+2OH?(aq)?NH3(g)+AlO?2(aq)

Explanation / Answer

MnO4(aq)+Br(aq)MnO2(s)+BrO3(aq)

split

MnO4- = MnO2

Br- = BrO3-

balance O

MnO4- = MnO2 + 2H2O

3H3O + Br- = BrO3-

balance H+

4H+ + MnO4- = MnO2 + 2H2O

3H3O + Br- = BrO3- + 9H+

balance charge

3e- + 4H+ + MnO4- = MnO2 + 2H2O

3H3O + Br- = BrO3- + 9H+ + 9e-

balance e

9e- + 12H+ + 3MnO4- = 3MnO2 + 6H2O

3H3O + Br- = BrO3- + 9H+ + 9e-

add all

3H3O + Br- + 9e- + 12H+ + 3MnO4- = 3MnO2 + 6H2O + BrO3- + 9H+ + 9e-

simplify

Br- + 3H+ + 3MnO4- = 3MnO2 + 3H2O + BrO3-

add OH-

Br- + 3H2O + 3MnO4- = 3MnO2 + 3H2O + BrO3- + 3OH-

simplify

Br- + 3MnO4- = 3MnO2 + BrO3- + 3OH-

b)

Ag(s)+CN(aq)+O2(g)Ag(CN)2(aq)

2Ag(s)+4CN(aq)+2O2+H2O(l)(g)2Ag(CN)2(aq)+2OH(aq) --> mass balance (oxygen) not correct

2Ag(s)+8CN(aq)+4O2+2H2O(l)(g)4Ag(CN)2(aq)+8OH(aq) --> charge balance not correct

4Ag(s)+2CN(aq)+O2+4H2O(l)(g)4Ag(CN)2(aq)+8OH(aq) --> charge balance not correct

4Ag(s)+8CN(aq)+O2+2H2O(l)(g)4Ag(CN)2(aq)+4OH(aq) --> correct

C)

NO2(aq)+Al(s)NH3(g)+AlO2(aq)

NO2- = NH3

Al = AlO2-

balance O

NO2- = NH3 + 2H2O

2H2O + Al = AlO2-

balance H

7H+ + NO2- = NH3 + 2H2O

2H2O + Al = AlO2- + 4H+

balance charge

6e- + 7H+ + NO2- = NH3 + 2H2O

2H2O + Al = AlO2- + 4H+ +3e-

balance e

6e- + 7H+ + NO2- = NH3 + 2H2O

4H2O + 2Al = 2AlO2- + 8H+ + 6e-

add all

4H2O + 2Al + 6e- + 7H+ + NO2- = NH3 + 2H2O + 2AlO2- + 8H+ + 6e-

simplify

2H2O + 2Al + NO2- = NH3 + 2AlO2- + H+

add OH-

OH- + 2H2O + 2Al + NO2- = NH3 + 2AlO2- + H2O

simplify

OH- + H2O + 2Al + NO2- = NH3 + 2AlO2-

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