Redox

• What are reducing agents in redox reactions?

  Electron donors
• What are oxidising agents in redox reactions?

  Electron acceptors
• What does oxidation involve?

  Loss of electrons
• What does reduction involve?

  Gain of electrons
• What is the oxidation process of zinc represented as?

  Zn → Zn$^{2+}$ + 2e$^{-}$
• What happens to the oxidation number during oxidation?

  It increases
• What happens to the oxidation number during reduction?

  It decreases
• What is the oxidation number of uncombined elements?

  Zero
• What is the oxidation number of sodium in NaCl?

  +1
• What is the oxidation number of chlorine in NaCl?

  -1
• What is the oxidation number of a monoatomic ion equal to?

  The ionic charge
• What is the oxidation number of Zn$^{2+}$?


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


  -1
• How do you find the oxidation number in a polyatomic ion?

  Sum equals the charge on the ion
• What is the oxidation number of carbon in CO$_{3}^{2-}$?


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


  -2
• What are the invariable oxidation numbers for Group 1 metals?

  +1
• What are the invariable oxidation numbers for Group 2 metals?

  +2
• What is the invariable oxidation number for aluminum?

  +3
• What is the invariable oxidation number for hydrogen in most compounds?

  +1
• What is the invariable oxidation number for fluorine?

  -1
• What is the invariable oxidation number for oxygen in most compounds?

  -2
• What is the oxidation number of oxygen in peroxides?

  -1
• How do you identify oxidation numbers of elements with variable oxidation numbers?

  Use oxidation number rules
• What is the oxidation number of chlorine in CaCl$_{2}$?


  -1
• What is the oxidation number of iron in FeCl$_{3}$?


  +3
• What does a reduction half equation show?

  Parts involved in reduction
• Where are electrons placed in a reduction half equation?

  On the left
• What does an oxidation half equation show?


  Parts involved in oxidation
• Where are electrons placed in an oxidation half equation?

  On the right
• What is the first step in balancing redox equations?

  Work out oxidation numbers
• How do you add electrons for oxidation?

  Add to products
• How do you add electrons for reduction?

  Add to reactants
• What must be checked after adding electrons in half equations?

  Sum of charges must equal
• What is done to balance oxygen in half equations?

  Add H$_{2}O$ to products
• What is done to balance hydrogen in half equations?

  Add H$^{+}$ to reactants
• How do you combine half equations?

  Ensure equal numbers of electrons
• What is the final step in combining half equations?

  Add and cancel electrons
• What is the half equation for MnO$_{4}^{-}$ to Mn$^{2+}$?


  MnO$_{4}^{-}$ + 8H$^{+}$ + 5e$^{-}$ → Mn$^{2+}$ + 4H$_{2}O$
• What is the half equation for SO$_{4}^{2-}$ to SO$_{2}$?


  SO$_{4}^{2-}$ + 4H$^{+}$ + 2e$^{-}$ → SO$_{2}$ + 2H$_{2}O$