Redox

• 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+?

  +1
• What is the oxidation number of 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 do you calculate the oxidation number of S in SO4$^{2-}$?


  • Combined oxygen has an oxidation number of -2.
  • 4 x -2 = -8.
  • The charge on the compound is -2.
  • Sum of oxidation numbers must equal -2.
  • So, -2 - (-8) = +6.
• Define oxidation in terms of electron transfer and oxidation number.

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

  Reduction is 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