Question

What would be the coefficient in front of H₂O if you balanced the following redox reaction in basic solution?

NO₂^-(aq) + Al(s) → NH₃(g) + AlO₂^-(aq)

Answer 1

The charge on nitrogen in NO2(-) is +3 and on nitrogen in NH3 is -3,so it is undergoing reduction

the charge of Al is 0 and in AlO2(-) is +3 so it is undergoing oxidation

Now it is divided into two half oxidation half and reduction half

Now since all other atoms are balanced now oxygen and hydrogen has to be balanced

oxygen atom is balanced by adding water molecules to side deficient in oxygen side

Now hydrogen atom is balanced by adding H+ ions

Since reaction is in basic medium OH- equal to number of H + ions is added on both side and then H+ and OH- on same side combine to form H2O molecule.

now charges are balanced by adding electrons to side deficient in negative charge

Now electron gain is made equal to electron loss by multiplying oxidation reaction by 2

now adding both the equation

Now simplifying

by putting the states and putting coefficient

coefficient in front of H2O is 1