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Oxidation is the loss of electrons Reduction is the gain of electrons The total reaction = redox reaction 2Mg(s) + O2(g) 2MgO(s) The half reactions = oxidation and/or reduction reactions Mg Mg+2 + 2eO2 + 4e- 2O-2 Mg(s) + O2(g) MgO(s) Mg Mg+2 + 2e- O2 + 4e- 2O-2 Mg loses 2 electrons to become Mg+2 O gains 2 electrons to become O-2 ( we have O2 molecule that contains 2 oxygen atom, both atoms are gaining electrons : O2 gains 4 electrons to become 2O-2) OXIDATION half reaction Mg Mg+2 + 2eMg loses electrons, so it is oxidized REDUCTION half reaction O2 + 4e- 2O-2 Oxygen gains electrons, so it is reduced An overall redox reaction consist of two half reactions # of electrons lost = # of electrons gained 2Mg 2Mg+2 + 4e- (multiply by 2 to get 4) O2 + 4e- 2O-2 2Mg + O2 + 4e- 2Mg+2 + 2O-2 + 4e2Mg + O2 2Mg+2 + 2O-2 Overall balanced equation: 2Mg(s) + O2(g) 2MgO(s) Ex: For the rxn between sodium and chlorine, write the chemical equation and the ionic equation: Na + Cl2→ NaCl Sodium loses an electron – oxidized Chlorine gains an electron – reduced Can also write the oxidation and reduction half reactions: Na → Na+ + 1eoxidation half rxn Cl2 + 2e- → 2Clreduction half rxn When combining half reactions make sure # egained = #e- lost. 2Na → 2Na+ + 2e- half rxn ×2 Cl2 + 2e- → 2Cl Total redox rxn 2Na+ Cl2 + 2e- → 2Cl- + 2Na+ + 2e 2Na+ Cl2 → 2Cl- + 2Na+ 2Na+ Cl2 → 2NaCl 1. 2. 3. 4. Fe + Br2 FeBr3 Ni + HgCl2 Hg + NiCl2 Sn+2 + Cu+2 Sn+4 + Cu CO + I2O5 CO2 + I2 Oxidation and reduction reaction = redox rxn Oxidation is loss of electrons and reduction is gain of electrons = transfer of electrons Those 2 reactions are occurring simultaneously 0 0 +2 -2 2Mg(s) + O2(g) 2MgO(s) Mg loses 2 e- to become Mg+2: it is oxidized › 2Mg 2Mg2+ + 4e- (ox. # increases) O gains 2 e- to become O-2: it is reduced › O2 + 4e- 2 O-2 (ox. # decreases) 0 0 +2 -2 2Mg(s) + O2(g) 2MgO(s) Oxidation half-reaction: 2Mg → 2Mg2+ + 4e- (ox. # increases) 2Mg loses 4 e- to become 2Mg+2: it is oxidized Mg was oxidized by of O2. Mg gave those e- to oxygen. Therefore, oxygen is OXIDAZING AGENT Reduction half-reaction: O2 + 4e- → 2 O-2 (ox. # decreases) O gains 2 e- to become O-2: it is reduced O2 was reduced by Mg. O2 accepted e- from magnesium. Therefore, Mg is REDUCING AGENT. In a redox reaction, the reducing agent is oxidized and the oxidizing agent is reduced. Loss of electrons 0 0 +2 -2 2Mg(s) + O2(g) 2MgO(s) Gain of electrons Substance oxidized Reducing agent Substance reduced Oxidizing Agent The terms oxidizing and reducing agents tell you what effect has a substance on its environment and what happens to it. For the following reaction: Ni + HgCl2 → Hg + NiCl2 A) Draw a diagram showing the loss and gain of electrons. B) Identify the substance oxidized, the substance reduced , the oxidizing agent and the reducing agent. C) Write the oxidation and reduction half reactions. For following reactions: 5CO + I2O5 → 5 CO2 + I2 2 Na + 2 H2O → 2NaOH + H2 Cl2 + 2NaBr → Br2 + 2NaCl 4NH3 + 7O2 → 4NO2 + 6H2O