CHEM 113 1st Edition Lecture 40Outline of Last Lecture I. Lewis acids and basesII. Transition metals as Lewis AcidsIII. ElectrochemistryOutline of Current Lecture IV. Redox chemistry revisitedV. Half-reaction method for balancing redox reactionsVI. Steps in the half-reaction methodVII. Balancing redox reactions in basic solutionsCurrent LectureI. Redox chemistry revisiteda. Oxidation is the loss of electrons and reduction is the gain of electrons. These processes occur simultaneouslyb. Oxidation results in an increase in the oxidation number (O#) while reduction results in a decrease in O#c. The oxidizing agent takes electrons from the substance being oxidized. The oxidizing agent is therefore reducedd. The reducing agent gives electrons to the substance being reduced. The reducing agent is therefore oxidizedII. Half-reaction method for balancing redox reactionsa. The half-reaction method divides a redox reaction into its oxidation and reduction half reactionsi. This reflects their physical separation in electrochemical cellsb. This method doesn’t requires assigning O#sThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.c. The half- reaction method is easier to apply to reactions in acidic or basic solutions which are common in electrochemical cellsIII. Steps in the half-reaction methoda. Divide the skeleton reaction into two half-reaction, each of which contains the oxidized and reduced forms of one of the speciesb. Balance the atoms and charges in each half-reactioni. First balance atoms other than O and H, then O, then Hii. Charge is balanced by adding electrons to the left since in the reduction reaction half-reaction (reactant gains them) and to the right side in the oxidation half- reaction (reactant loses them)c. If necessary, multiply one or both half-reaction by an integer so that the number of e- gained in reduction= number of e- lost in oxidationd. Add the balanced half-reactions, and include states of mattere. Check the atoms and charges are balancedIV. Balancing redox reactions in basic solutionsa. An acidic solution contains H+ ions and H2O, we use H+ to balance H atoms, but basic solutions contain OH- ions and H2Ob. To balance H atoms, we proceed as if in acidic solution ( through step 4) and thenadd on OH- ion to both sides of the equation for every H+ ion presentc. For every OH- ion and H+ ion that appear on the same side of the equation we form an H2O moleculed. Excess H2O molecules are canceled in the final step, when we cancel electrons and other common
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