Balance the following equation in basic medium? Zn(s) + NO3^- (aq)----> NH3(aq)+ Zn (OH)4 ^2- (aq)

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This is a redox reaction. It can be split into two half-reactions, one oxidation and other reduction. In basic medium, the oxygen and hydrogen atom balancing has to be done with OH-/H2O. Thus,

Oxidation half-reaction: Zn  + 4 OH- → Zn(OH)42- + 2 e-  ------ * 4 (for charge balance)

Reduction half-reaction: NO3- + 6 H2O + 8 e-→ NH3 + 9 OH

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Overall: 4Zn + NO3- + 6 H2O + 7 OH-  → 4 Zn(OH)42- + NH3

Adding the suffixes to indicate the physical states of the species:

4Zn(s) + NO3^- (aq.) + 6H2O + 7OH- → NH3 (aq.) + 4Zn (OH)4 ^2- (aq.)

 Sometimes NH3 (aq.) is written as NH4OH, and then the balanced chemical reaction would require one more molecule of H2O in the left side:

 4Zn(s) + NO3^- (aq.) + 7H2O + 7OH- → NH4OH (aq.) + 4Zn (OH)4 ^2- (aq.)

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