Reduction & Oxidation

 Originally defined as elements gaining (combining) with oxygen  Most basic example is combustion  In combustion, the element carbon is combined with oxygen → CO 2  Burning Graphite Burning Graphite  Burning pure Carbon - Diamonds Burning pure Carbon - Diamonds

 Other non-metallic elements unite with elements in a similar manner ◦ H 2, Sb, Na will burn in Cl 2 ◦ Fe will burn in F 2  Sodium & Chlorine Gas Video 1 Sodium & Chlorine Gas  Sodium & Chlorine Gas Video 2 Sodium & Chlorine Gas  Both videos show sodium “burning” in pure chlorine gas  ∴ oxidation can include elements other than oxygen

 Oxidation was redefined as the process by which electrons are removed from an atom or ion.  Reduction was then defined as the process by which any atom or ion gains electrons.

 2 Mg (s) + O 2 (g) → 2 MgO (s)  In Ionic form:  Note: ◦ Magnesium and oxygen gases are both elements and have no charge ◦ We say that the magnesium has been oxidized to MgO by the reaction with oxygen gas ◦ Considering the charges, the metal has gone from a 0 charge to 2+ and the non-metal from 0 charge to 2- Mg 0 + O 2 0 →Mg 2+ + O

 Look at change in ion charge as a function of electrons: ◦  (charge is conserved, 0 charge on both sides) ◦  (charge is conserved, 4- charge on both sides)  Mg is oxidized (combines with oxygen) ◦ Mg gains a positive charge by becoming an ion ◦ This occurs by a loss of electrons 2Mg 0 →2Mg 2+ +4e - O 2 0 →2O e -

 Mg (s) + Cl 2(g) → MgCl 2(s)  Ionic equation:  Mg 0 + Cl 2 0 → Mg Cl -  As a function of electrons:  ◦ (charge is conserved, 0 charge on both sides)  ◦ (charge is conserved, 2- charge on both sides) Mg 0 →Mg 2+ +2e - Cl 2 0 →2Cl - + 2e -

 Mg is oxidized  Mg gains a positive charge to become an ion  This occurs by a loss of electrons  A complementary reaction is that a Cl atom becomes a Cl - ◦ Cl is reduced to a negative ion ◦ This occurs by a gain of electrons ◦ Thus Cl has been reduced.

 O xidizing I s L osing  R eduction I s G aining

 Identify which element is experiencing reduction and which element is experiencing oxidation ◦ Fe 3+ + Cu + → Fe 2+ + Cu 2+  Function of elections ◦ Fe e - → Fe 2+ ◦ Cu + → Cu 2+ +1e - Gain of electrons - reduction Loss of electrons - oxidation