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in Oxidation-Reduction Reactions by (49.4k points)

Balance the following reactions using Ion Electron method :
(i) MnO4 + H2O2 ➝ MnO2 + O2 + OH
(ii) AsO33- + H2O + I2 ➝ AsO43- + H+ + I
(iii) Cl2O7 +  H2O2 ➝ ClO2 + O2 + H+
(iv) Cr2O72-+ SO2 ➝ Cr3+ + SO42-

1 Answer

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Best answer

(i) MnO4 + H2O2 ➝ MnO2 + O2 + OH

(a) To balance oxygen atoms, add H2O to right side
MnO4 ➝ MnO2 + 2H2O

(b) To balance hydrogen atoms, add H+ ions to left side
MnO4 + 4H+ ➝ MnO2 + 2H2O
∵ The reaction is in basic medium, OH are added to right side.
MnO4 + 4H2O ➝ MnO2 + 2H2O + 4OH

(c) To balance charge, electrons are added to left side
MnO4 + 4H2O ➝ MnO2 + 2H2O + 4OH– …(1)

(a) To balance hydrogen atoms, add H+ ions to right side
H2O2 ➝ O2 + 2H+
∵ Reaction is in basic medium, add OH ions to left side
H2O2 + 2OH➝ O2 + 2H2O

(b) To balance charge, electrons are added to right side
H2O2 + 2OH ➝ O2 + 2H2O + 2e …(2)
Multiply equation 1 by 2 and equation 2 by 3, and add, we get

This is balanced equation.

(ii) AsO33- + H2O + I2 → AsO43- + H+ + I

(a) To balance oxygen atom, add H2O to left side
AsO33- + H2O ➝ AsO43-

(b) To balance hydrogen atoms, add H+ ions to right side
AsO33- + H2O ➝ AsO43- + 2H+

(c) To balance charge, electrons are added to right side
AsO33- + H2O ➝ AsO43- + 2H+ + 2e …(1)

Balancing I, I2 ➝ 2I

(a) To balance charge, electrons are added to leftside
I2 + 2e ➝ 2I …(2)
Add eq. (1) and (2)

This is balanced equation.

(iii) Cl2O7 + H2O2 ➝ ClO2 + O2 + H+

Balancing Cl, Cl2O7 ➝ 2ClO2

(a) To balance oxygen atoms, add H2O to right side
Cl2O7 ➝ 2ClO2 + 3H2O

(b) To balance hydrogen atoms add H+ ion to left side
Cl2O7 + 6H+ ➝ 2ClO2 + 3H2O

(c) To balance charge, electrons are added to left side
Cl2O7 + 6H+ + 8e ➝ 2ClO2 + 3H2O …(1)

(a) To balance hydrogen atoms, add H+ ions to right side
H2O2 ➝ O2 + 2H+

(b) To balance charge, add electrons to right side
H2O2 ➝ O2 + 2H+ + 2e …(2)
Multiply eq. (1) by 1 and eq. (2) by 4, and add, we get

This is balanced equation.

(iv) Cr2O72- + H2O ➝ Cr3+ + SO42-

Balancing Cr, Cr2O72- ➝ 2Cr3+ 

(a) To balance oxygen atoms, add H2O to right side
Cr2O72- ➝ 2Cr3+ + 7H2O

(b) To balance hydrogen atoms add H+ ion to left side
Cr2O72- + 14H+ ➝ 2Cr3+ + 7H2O

(c) To balance charge, electrons are added to left side
Cr2O72- + 14H+ + 6e ➝ 2Cr3+ + 7H2O …(1)

(a) To balance oxygen atoms, add H2O to left side
SO2 + 2H2O ➝ SO42-

(b) To balance hydrogen atoms add H+ ions to right side
SO2 + 2H2O ➝ SO42- + 4H+
(c) To balance charge, add electrons to right side.
SO2 + 2H2O ➝ SO42- + 4H+ + 2e … (2)
Multiply eq. (1) by 1 and eq (2) by 3, and add, we get

This is balanced equation.

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