Question

When the following equation is balanced properly under acidic conditions, what are the coefficients of the species shown? HNO2 + Ni2+NO3- + Ni Water appears in the balanced equation as a (reactant, product, neither) with a coefficient of . (Enter 0 for neither.) How many electrons are transferred in this reaction?

Answer 1

HNO₂ + Ni²⁺ NO₃^- + Ni

The two half reactions are
Ni²⁺ Ni --------------------------------------------------------(1)
HNO₂    NO₃^- --------------------------------------------------------(2)

So, considering the first half reaction
Ni²⁺ + 2e^-     Ni -------------------------------------------------(3)

The second half-reaction needs one more oxygen atom on the left, so we add one H2O molecule.
HNO₂ + H₂O   NO₃^-

The second half-reaction needs three hydrogen atoms on the right to balance the three hydrogen atoms on the left, so we add 3 H+ ions to the right.
HNO₂ + H₂O   NO₃^- + 3H⁺

Balance the charge by adding electrons, e-.
HNO₂ + H₂O   NO₃^- + 3H⁺ + 2e^- ----------------------------------------(4)

Adding equation (3) and (4), we get;

Ni²⁺ + 2e^- + HNO₂ + H₂O   Ni +  NO₃^- + 3H⁺ + 2e^-

Ni²⁺ +  HNO₂ + H₂O     Ni +  NO₃^- + 3H⁺  

This reaction requires 2 electrons.