Final answer:
To complete and balance the given redox reaction in an acidic solution, one must first balance the individual half-reactions for mass and charge, then combine them to ensure the electrons lost equal the electrons gained.
Step-by-step explanation:
The student question asks to complete and balance the following equation in an acidic solution: NO₂⁻(aq) + Cr₂O₇²⁻(aq) → Cr³⁻(aq) + NO₃⁻(aq). To solve this, it is a redox reaction where both half-reactions must be balanced for mass and charge, then combined to give the balanced net ionic equation.
First, balance the half-reactions individually in acidic conditions. For the reduction half, Cr₂O₇²⁻ will gain electrons to become Cr³⁻. For the oxidation half, NO₂⁻ will lose electrons to become NO₃⁻. After balancing for mass and charge by adding H⁻ and H₂O where necessary and adjusting the coefficients, we then combine the two balanced half-reactions.
It is crucial to ensure that the number of electrons lost in the oxidation half-reaction equals the number of electrons gained in the reduction half-reaction. After balancing the electrons, combine the half-reactions to cancel out the electrons, and you get the balanced net equation for this redox reaction.