Redox reactions

• What are reducing agents in redox reactions?

  Reducing agents are electron donors.
• What are oxidising agents in redox reactions?

  Oxidising agents are electron acceptors.
• What is oxidation in terms of electron transfer?

  Oxidation is the process of electron loss.
• What is the oxidation number change during the oxidation of zinc?

  Oxidation involves an increase in oxidation number.
• What is the oxidation reaction of zinc?

  Zn → Zn$^{2+}$ + 2e$^{-}$
• What is reduction in terms of electron transfer?

  Reduction is the process of electron gain.
• What is the oxidation number change during the reduction of chlorine?

  Reduction involves a decrease in oxidation number.
• What is the reduction reaction of chlorine?

  Cl$_{2}$ + 2e$^{-}$ → 2Cl$^{-}$
• What are the rules for assigning oxidation numbers?

  1. All uncombined elements have an oxidation number of zero.
  2. The oxidation numbers of the elements in a compound add up to zero.
  3. The oxidation number of a monoatomic ion is equal to the ionic charge.
  4. In a polyatomic ion, the sum of the individual oxidation numbers adds up to the charge on the ion.
  5. Several elements have invariable oxidation numbers in their common compounds.
• What is the oxidation number of uncombined elements like Zn, Cl$_{2}$, O$_{2}$, and Ar?


  All have an oxidation number of zero.
• What is the oxidation number of sodium in NaCl?

  Na has an oxidation number of +1.
• What is the oxidation number of chlorine in NaCl?

  Cl has an oxidation number of -1.
• What is the oxidation number of Zn$^{2+}$?


  It is +2.
• What is the oxidation number of Cl$^{-}$?


  It is -1.
• What is the oxidation number of carbon in CO$_{3}^{2-}$?


  It is +4.
• What is the oxidation number of oxygen in CO$_{3}^{2-}$?


  It is -2.
• What is the sum of oxidation numbers in a compound?

  The sum must equal zero.
• What is the oxidation number of chlorine in CaCl$_{2}$?


  It is -1.
• How do you determine the oxidation number of an element with variable oxidation numbers?

  Always work out the oxidation per one atom of the element.
• What is the oxidation number of Fe in FeCl$_{3}$?


  It is +3.
• What are the steps to write half equations for redox reactions?

  1. Work out oxidation numbers for the element being oxidised/reduced.
  2. Add electrons equal to the change in oxidation number.
  3. Check that the sum of the charges on both sides equals.
• What is the half equation for the oxidation of zinc?

  Zn → Zn$^{2+}$ + 2e$^{-}$
• How do you balance half equations with varying amounts of oxygen?

  Add H$_{2}O$, H$^{+}$, or OH$^{-}$ ions as needed.
• What is the half equation for the reduction of MnO$_{4}^{-}$ to Mn$^{2+}$?


  MnO$_{4}^{-}$ + 8H$^{+}$ + 5e$^{-}$ → Mn$^{2+}$ + 4H$_{2}O$
• What is the purpose of combining half equations in redox reactions?

  To create a full redox equation with equal numbers of electrons.
• How do you combine half equations for redox reactions?

  Ensure equal numbers of electrons in both half equations before combining.
• What is the final balanced equation for the reaction involving MnO$_{4}^{-}$ and C$_{2}O_{4}^{2-}$?


  2MnO$_{4}^{-}$ + 16H$^{+}$ + 5C$_{2}O_{4}^{2-}$ → 2Mn$^{2+}$ + 10CO$_{2}$ + 8H$_{2}O$
• What is the half equation for the change SO$_{4}^{2-}$ to SO$_{2}$?


  SO$_{4}^{2-}$ + 4H$^{+}$ + 2e$^{-}$ → SO$_{2}$ + 2H$_{2}O$
• What is the final balanced equation for the reaction involving SO$_{4}^{2-}$ and I$^{-}$?


  8I$^{-}$ + SO$_{4}^{2-}$ + 10H$^{+}$ → H$_{2}S$ + 4I$_{2}$ + 4H$_{2}O$
• What are the key concepts of redox reactions?

  • Oxidation involves electron loss and an increase in oxidation number.
  • Reduction involves electron gain and a decrease in oxidation number.
  • Oxidising agents accept electrons, while reducing agents donate electrons.
  • Half equations represent the oxidation and reduction processes separately.