CHEM105 1nd Edition Lecture 9 Outline of Last Lecture • Solubility rules• precipitation reactions Outline of Current Lecture • Oxidation-Reduction Reactions (Redox)• Oxidation: the loss of electrons• Reduction: the gain of electronsCurrent LectureMnemonics: LEO the lion says GEROLI RIGQ: How do you tell when a redox reaction has occurred?A: Look at the oxidation numbers of the reactants and products. The rules for assigning oxidation numbers are on page 165-166 of your text.• An element is reduced if its oxidation number gets lowered (reduced). [+4 to +2, +3 to 0, -2 to -5 are all reductions]• An element is oxidized if its oxidation number goes up.[0 to +3, -5 to +2, -3 to -1 are all oxidation]• The compound that contains the element that gets reduced is called the oxidizing agent.• The compound that contains the element that is oxidized is called the reducing agent.Q: Which of the following are redox reactions?• Na(s) + Cl2(g) ------> NaCl(s) (Redox) • S(s) + O2(g) ------> SO3(g) (Redox) • Pb(NO3)2(aq) + KI(aq) -----> PbI2(S) + KNO3(aq) (Not Redox)• Zn(s) + HCl(aq) -----> ZnCl2(aq) + H2(g) (Redox)• H2SO4(aq) + CH2O-----> H2S(aq) +CO2 +H2O
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