Balance the following equation in acidic solution using the lowest possible inte

Question

Balance the following equation in acidic solution using the lowest possible integers

and give the coefficient of H+.

H2CO(aq) + S(s) => H2S(g) + CO2(g)

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Balance the following equation in acidic solution using the lowest possible integers and give the coefficient of water.
NH3(aq) + ClO-(aq) ? N2H4(aq) + Cl-(aq)

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Balance the following equation in acidic solution using the lowest possible integers and give the coefficient of H+.
Zn(s) + NO3-(aq) ? Zn2+(aq) + N2(g)

Explanation / Answer

First half-reaction:
Zn(s) --> Zn2+(aq) + 2e-
NH3 + ClO- --> N2H4 + Cl-

so in the above equation, nitrogen undergoes oxidation (going from its -3 oxidation state to its -2 state), and Cl undergoes reduction (going from +1 to -1)

half equations...

NH3 --> N2H4
2NH3 --> N2H4
2NH3 --> N2H4 + 2H+
since it's in base, use 2 hydroxy groups to balance the charge on the right hand side of the equation
2NH3 --> N2H4 + 2H+ + 2OH-
now it's unbalanced, add 2 hydroxy groups to the LHS of the equation...
2NH3 + 2OH- --> N2H4 + 2H+ + 2OH-
note: the 2H+ and 2OH- on the RHS combine together to form 2H2O molecules, soo...
2NH3 + 2OH- --> N2H4 + 2H2O
finally, add two electrons to balance the charges
2NH3 + 2OH- --> N2H4 + 2H2O + 2e

next one (reduction)...

ClO- --> Cl-
ClO- --> Cl- + H2O
ClO- + 2H+ --> Cl- + H2O
use hydroxy groups to balance the charge...
ClO- + 2H+ + 2OH- --> Cl- + H2O
now it's unbalanced, so add 2 hydroxy's to the RHS
ClO- + 2H+ + 2OH- --> Cl- + H2O + 2OH-
note: the 2H+ and 2OH- on the LHS of the equation combines to form 2H2O molecules..
ClO- + 2H2O --> Cl- + H2O + 2OH-
one H2O molecule cancels out...
ClO- + H2O --> Cl- + 2OH-
now the charge is unbalanced, so add 2 electrons to the LHS
ClO- + H2O + 2e --> Cl- + 2OH-

now combine these two half equations to get your full redox eqn...

2NH3 + 2OH- + ClO- + H2O + 2e --> Cl- + 2OH- + N2H4 + 2H2O + 2e

electrons cancel out perfectly, OH's cancel out perfectly, and one H2O molecule cancels out...

2NH3 + ClO- --> Cl- + N2H4 + H2O

  
Second half-reaction:
NO3-(aq) --> N2(g)

2NO3-(aq) --> N2(g)

2NO3-(aq) --> N2(g) + 6H2O

12H+ + 2NO3-(aq) --> N2(g) + 6H2O

10e- + 12H+ + 2NO3-(aq) --> N2(g) + 6H2O

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