Oxidation Reduction and Redox Reactions

• What is an oxidation number?


  The number of electrons an atom uses to bond with any other atom
• What is the oxidation number of an uncombined element such as C, H, O2?

  0
• What is the oxidation number of combined oxygen such as in H2O?

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

  • 1
• What is the oxidation number of combined hydrogen such as in NH3, H2S?

  +1
• What is the oxidation number of hydrogen in metal hydrides such as LiH?

  • 1
• What is the oxidation number of a simple ion?


  Charge on the ion
• What is the oxidation number of Na+ and Cl-?

  Na+ → +1 ; Cl- → -1
• What is the oxidation number of combined fluorine such as in NaF, CaF2?

  • 1
• How is an element with more than one stable oxidation number indicated?

  Written as a Roman numeral
• What is the oxidation number of Fe in iron (III) chloride?

  +3
• What are oxyanions?


  Negative ions that have an element along with oxygen
• What is the oxidation number of S in SO4$^{2-}$?


  +6
• How is the oxidation number of S in SO4$^{2-}$ calculated?


  Combined oxygen has an oxidation number of -2, so 4 x -2 = -8, and the sum must equal -2.
• Define oxidation in terms of electron transfer and oxidation number.

  Oxidation is the loss of electrons and an increase in oxidation number.
• Define reduction in terms of electron transfer and oxidation number.

  Reduction is the gain of electrons and a decrease in oxidation number.
• What is a redox reaction?

  A reaction in which both oxidation and reduction takes place.
• What is the oxidation number of a metal?

  0, because it is an uncombined element.