Balance the redox reaction in acidic solution: SO_3^2- + Fe^3+ rightarrow Fe^2+

Question

Balance the redox reaction in acidic solution: SO_3^2- + Fe^3+ rightarrow Fe^2+ + SO_4^2- Separate the equation into two half-reactions Balance the atoms other than O and H in each half-reaction Add H_2O to balance O atom and H to balance H atoms Add electrons to one side of each half-reaction to balance the charge If necessary, equalize the number of electrons in the two half reactions by multiplying the half-reactions by appropriate coefficients Add the two half-reactions together and balance the final equation by inspection. Balance the redox reaction in acidic solution: CN^-+ mnO_4 rightarrow CNO^-+ mnO_2 Separate the equation into two half-reactions Balance the atoms other than O and H in each half-reaction Add H_2O to balance O atoms and H to balance H atoms Add electrons to one side of each half-reaction to balance the charges If necessary, equalize the number of electrons in the two half reactions by multiplying the half-reactions by appropriate coefficients Add the two half-reactions together and balance the final equation by inspection.

Explanation / Answer

Q!.

SO3-2 + Fe+3 --> Fe+2 + SO4-2

half reactions

Fe+3 --> Fe+2

SO3-2 --< SO4-2

balance all other than O and H

Fe+3 --> Fe+2

SO3-2 --< SO4-2

balance O by adding H2O

Fe+3 --> Fe+2

H2O + SO3-2 --< SO4-2

balance H form H+

Fe+3 --> Fe+2

H2O + SO3-2 --< SO4-2 + 2H+

add electrons

e- + Fe+3 --> Fe+2

H2O + SO3-2 --< SO4-2 + 2H+ + 2e-

balance eletrcons

2e- + 2Fe+3 --> 2Fe+2

H2O + SO3-2 --> SO4-2 + 2H+ + 2e-

add half reactions

2e- + 2Fe+3 + H2O + SO3-2 --> 2Fe+2 + SO4-2 + 2H+ + 2e-

cancel common terms

2Fe+3 + H2O + SO3-2 --> 2Fe+2 + SO4-2 + 2H+

add OH-

2OH- + 2Fe+3 + H2O + SO3-2 --> 2Fe+2 + SO4-2 + 2H+ + 2OH-

2OH- + 2Fe+3 + H2O + SO3-2 --> 2Fe+2 + SO4-2 + 2H2O

2OH- + 2Fe+3 + SO3-2 --> 2Fe+2 + SO4-2 + H2O

Q2.

CN-+ MnO4- --> CNO- + MnO2

CN- --> CNO-

MnO4- --> MnO2

then

H2O + CN- --> CNO-

MnO4- --> MnO2 + 2H2O

balance H

H2O + CN- --> CNO- + 2H+

4H+ + MnO4- --> MnO2 + 2H2O

balance charges

H2O + CN- --> CNO- + 2H+ + 2e-

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

balance e-

3H2O + 3CN- --> 3CNO- + 6H+ + 6e-

6e- + 8H+ + 2MnO4- --> 2MnO2 + 4H2O

add all

3H2O + 3CN- + 6e- + 8H+ + 2MnO4-   --> 3CNO- + 6H+ + 6e- +  2MnO2 + 4H2O

cancel comon terms

3CN- + 2H+ + 2MnO4-   --> 3CNO- +2MnO2

add OH-

2OH- + 3CN- + 2H+ + 2MnO4-   --> 3CNO- +2MnO2 + 2OH-

2H2O + 3CN- + 2MnO4- --> 3CNO- +2MnO2 + 2OH-

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