Redox Reaction Examples with Oxidation States

📚 Quick Study Guide

• ⚛️ Redox Reaction Definition: A chemical reaction involving the transfer of electrons between two species. One species is oxidized (loses electrons), and another is reduced (gains electrons).
• 🔢 Oxidation State Rules:
  • 🥇 Elements in their standard state have an oxidation state of 0 (e.g., $O_2$, $Cu$).
  • 🥈 Oxygen usually has an oxidation state of -2 (except in peroxides like $H_2O_2$ where it's -1).
  • 🥉 Hydrogen usually has an oxidation state of +1 (except in metal hydrides like $NaH$ where it's -1).
  • 🏅 The sum of oxidation states in a neutral compound is 0; in a polyatomic ion, it equals the ion's charge.
• ⬇️ Oxidation: Increase in oxidation state (loss of electrons).
• ⬆️ Reduction: Decrease in oxidation state (gain of electrons).
• ⚖️ Balancing Redox Reactions: Use either the oxidation number method or the half-reaction method. Key steps include assigning oxidation numbers, identifying oxidation and reduction, balancing atoms, and balancing charge.

🧪 Practice Quiz

1. Which of the following reactions is a redox reaction?
   1. A. $AgNO_3(aq) + NaCl(aq) \rightarrow AgCl(s) + NaNO_3(aq)$
   2. B. $HCl(aq) + NaOH(aq) \rightarrow NaCl(aq) + H_2O(l)$
   3. C. $2H_2O(l) \rightarrow 2H_2(g) + O_2(g)$
   4. D. $NH_3(aq) + H_2O(l) \rightarrow NH_4^+(aq) + OH^-(aq)$
2. In the reaction $Zn(s) + Cu^{2+}(aq) \rightarrow Zn^{2+}(aq) + Cu(s)$, which species is oxidized?
   1. A. $Cu^{2+}(aq)$
   2. B. $Zn(s)$
   3. C. $Cu(s)$
   4. D. $Zn^{2+}(aq)$
3. What is the oxidation state of sulfur in $H_2SO_4$?
   1. A. +2
   2. B. +4
   3. C. +6
   4. D. -2
4. In the following reaction, which element is reduced? $2Fe^{3+}(aq) + Sn^{2+}(aq) \rightarrow 2Fe^{2+}(aq) + Sn^{4+}(aq)$
   1. A. Fe
   2. B. Sn
   3. C. O
   4. D. H
5. What is the oxidation state of oxygen in $OF_2$?
   1. A. -2
   2. B. +2
   3. C. -1
   4. D. +1
6. Which of the following half-reactions represents an oxidation?
   1. A. $Fe^{3+}(aq) + e^- \rightarrow Fe^{2+}(aq)$
   2. B. $Sn^{2+}(aq) \rightarrow Sn^{4+}(aq) + 2e^-$
   3. C. $Cl_2(g) + 2e^- \rightarrow 2Cl^-(aq)$
   4. D. $MnO_4^-(aq) + 8H^+(aq) + 5e^- \rightarrow Mn^{2+}(aq) + 4H_2O(l)$
7. In the reaction $MnO_2 + 4HCl \rightarrow MnCl_2 + 2H_2O + Cl_2$, which element is oxidized?
   1. A. Mn
   2. B. H
   3. C. O
   4. D. Cl