Transcript Slide 1
Oxidation Is often thought of as a combination with oxygen( rusting burning) 2H2(g) + O2(g) ----> 2H2O(g) CH4(g) + 2O2 ----> 2H2O(g) + CO2 Reduction Is thought as the removal of oxidation from a compound Examples 2Fe2O3 (s) --> 4Fe(s) + 3O2(g) ZnO(s) +C(s) Zn(s) + CO(g) Oxidation/Reduction Has a broader definitions and have been recognized to occur at the same time They are complimentary processes Redox stands for REDuction /Oxidation Oxidation: Loss of electron Reduction: Gain Electrons How to Remember Redox? As a mnemonic remember LEO says GER Loss of Electrons = Oxidation Gain Electrons = Reduction What Is Oxidation/Reduction? 2Na(s) + Cl2(s) ---> 2NaCl(s) Is this a ReDox Reaction? Why and Why NOT? Yes Because Na loss an electron and become Na+ ( Na ---> Na+ + e Cl2 gained electron and become Cl(Cl2 + e- --> 2 Cl-) Is it possible to oxidize a material without reducing something else? No A lost of electron is taken up by something else Oxidizing /reducing Agent Reducing agent Causes reduction by being oxidized itself Oxidation agent Cause oxidation by being reduced itself 2Na + Cl2(g) 2NaCl(s) Which is oxidizing agent? The one reduced Cl2 Which is reducing agent? The one oxidized Na Recap Loss of Electron = Oxidation Gain of Electrons = Reduction Substance oxidized is the reducing agent Substance reduced is the oxidizing agent Note: Oxidation reduction occurs between metals and nonmetals Homework #3 p. 602 Identify which is oxidized and reduced a) 6Na(s) + N2(g) --> 2Na3N(s) b) Mg(s) + Cl2(g) ---> MgCl2(s) c) 2Al(s) + 3Br2(l) --> 2AlBr3(s) d) 4Fe(s) + 3O2(g) --> 2Fe2O3(s) Ans. Na, N2/ Mg,Cl2/ Al, Br2/ Fe, O2 How to assign Oxidation States Any element when not combined with atoms of a different element, has an oxidation # of zero( O in O2 is zero) Any simple monatomic ion has an oxidation number equal to its charge(Na+ is +1, O-2 is -2) The sum of the oxidation numbers of all of the atoms in a formula must equal the charge written for the formula.( If the oxidation number of O is -2, then in CO22-, the oxidation # of C is +4. In compounds, the oxidation numbers of IA metals is +1, IIA is +2, IIIA is +3 In Ionic compounds, the oxidation number of a nonmetal or polyatomic ion is equal to the charge of its associated ion. ( CuCl2, Cl is -1) F is always -1, O is always -2( unless combine with F), H is usually +1 Examples Assign Oxidation states to all atoms in the following molecules or ions a) SO3 b) SO42c) N2O5 d) PF3 (6) +[(-2)(3)] (6)+[(-2)(4)] [(5)(2)]+[(-2)(5) (3) +[(-1)(3)] (+6) +(-6) (+6)+(-8) (10)+(-10) (3)+(-3) Redox between Nonmetals Ex: CH4 + 2O2(g) ---> CO2(g) + 2H2O -4 +1 0 +4 -2 +1 -2 Which one appear to have lost electron? -->Carbon ( from -4 to +4) --> increased oxidation Which one appears to have lost electron? - Oxygen( From 0 to -2) - Reduced oxidation Practice Identify the following reactions as redox or nonredox and identify the oxidizing/reducing agent PbO(s) + CO(g) --> Pb(s) + CO2(g) CaCO3(s) --> CaO(s) + CO2(g) S(s) +O2(g) --> SO2(g)