1.7 - 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 number of uncombined elements?

  Zero
• How do oxidation numbers in a compound sum up?

  They add up to zero
• What is the oxidation number of Na in NaCl?

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

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

  Equal to its ionic charge
• What is the oxidation number of Zn in Zn2+?

  +2
• What is the oxidation number of Cl in Cl-?

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

  Sum equals the ion's charge
• What is the oxidation number of C in CO3$^{2-}$?


  +4
• What is the oxidation number of O in CO3$^{2-}$?


  -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 Al?

  +3
• What is the oxidation number of H in most compounds?

  +1
• What is the oxidation number of H in metal hydrides?

  -1
• What is the oxidation number of F in compounds?

  -1
• What is the oxidation number of Cl, Br, and I in most compounds?

  -1
• What is the oxidation number of O in most compounds?

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

  -1
• How do you determine the oxidation number of Cl in CaCl2?

  -1
• What is the oxidation number of Fe in FeCl3?

  +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 are the steps to balance redox equations?

  1. Determine oxidation numbers.
  2. Add electrons for oxidation/reduction.
  3. Check charge balance.
• How do you balance half equations with varying amounts of O?

  Add H+, OH-, and H2O
• What is the half equation for MnO4$^{-}$ to Mn2+?


  MnO4$^{-} +$$8H+$$+$$5e^{-} \rightarrow Mn^{2+} +$$4H2O$
• What is the purpose of combining half equations?

  To create a full redox equation
• How do you ensure equal electrons in half equations?

  Multiply the half equations
• What is the final redox equation for the combination of half equations?

  8I<latex>^{-} + SO4^{2-} + 10H^{+} \rightarrow H2S + 4I2 + 4H2O
• What are the steps to write a half equation for SO4<latex>^{2-} \rightarrow SO2?

  1. Balance change in O.N. with electrons.
  2. Add H2O to balance O's.
  3. Add H+ to balance H's.
  4. Check charge balance.
• What is the half equation for SO4<latex>^{2-} \rightarrow SO2?


  SO4$^{2-} +$$4H+$$+$$2e^{-} \rightarrow SO2 +$$2H2O$
• What is the final redox equation for the combination of SO4<latex>^{2-} \rightarrow SO2?


  8I$^{-} +$$SO4^{2-} +$$10H^{+} \rightarrow H2S +$$4I2 +$$4H2O$
• What are the steps to combine half equations?

  1. Ensure equal electrons.
  2. Add half equations together.
  3. Cancel electrons.