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How to Balance Redox Equations?

How do you balance these redox reaction equations?

  • Note: Charges are enclosed in parentheses. 1. Zn + NO3 (-) -> NH3 + Zn(OH)4 (2-) 2. Sn (2+) + Cr2O7 (2-) -> Sn (4+) + Cr (3+) 3. MnO4 (2-) -> MnO2 + MnO4 (-)

  • Answer:

    1. Oxidation: [Zn + 4H2O = Zn(OH)4^2- + 4H+ + 2e] x 4 Reduction: NO3^- + 9H+ 8e= NH3 + 3H2O Overall: 4Zn + NO3- + 13H2O = 4Zn(OH)4^2- + NH3 + 7H+ 2. Oxidation: [Sn^2+ = Sn^4+ + 2e] x 3 Reduction: Cr2O7^2- + 14H+ + 6e = 2Cr3+ + 7H2O Overall: 3Sn^2+ + Cr2O7^2- + 14H+ = 3Sn^4+ + 2Cr^3+ + 7H2O 3. Oxidation: [MnO4^2- = MnO4^- + e] x 6 Reduction: MnO4^2- + 4H+ + 6e = MnO2 + 2 H2O Overall: 7MnO4^2- + 4H+ = MnO2 + 6MnO4^- + 2H2O That's it!n_n

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the most easiest method for balancing redox reactions is as follows: 1. find the species being oxidised and reduced 2. calculate the change in oxidation no. for d species being reduced and oxidised 3. reduce the change in o.s to the simplest ratios and cross multiply i.e. multiply d oxidised species with change in o.s of d reduced species and vise versa on both sides of the eqn 4. balance all othr atoms expt hydrogen nd oxygen 5. balance oxygen ND HYDROGEN on both sides by adding H+ in case of acidic med and OH- in basic med. nd add H2O on the other side for each H+ 6. Balance charge on both sides by adding electrons

ABHIJAY

Zn + 4 H2O = Zn(OH)4 2- + 4 H+ + 2e- ) x 4 NO3- + 9 H+ + 8e-= NH3 + 3 H2O 4 Zn + NO3- +13 H2O = 4 Zn(OH)4 2- + NH3 + 7 H+ because the reaction occurs in basic solution add 7 OH- on the left and on the right side ( remember that 7 H+ + 7 OH- = 7 H2O) 4 Zn + NO3- + 13 H2O + 7 OH- = 4 Zn(OH)4 2- + NH3 + 7 H2O cancel any duplications on the left and on the right side 4 Zn + NO3- + 6 H2O + 7 OH- = 4 Zn(OH)42- + NH3 Sn2+ = Sn4+ + 2e- ) x 3 Cr2O72- + 14 H+ + 6e-= 2 Cr3+ + 7 H2O 3 Sn2+ + Cr2O72- + 14 H+ = 3 Sn4+ + 2 Cr3+ + 7 H2O MnO4 2- + 4 H+ + 2e-= MnO2 + 2 H2O MnO4 2- = MnO4 - + 1e- ) x 2 3 MnO4 2- + 4 H+ = MnO2 + 2 MnO4 - + 2 H2O in basic solution add 4 OH- on the left and on the right side 3 MnO4 2- + 2 H2O = MnO2 + 2 MnO4 - + 4 OH-

Dr.A

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