OxidationReductionNotes

OxidationReductionNotes - A. Oxidation Early chemists saw...

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A. Oxidation Early chemists saw “oxidation” reactions only as the combination of a material with oxygen to produce an oxide. For example, when methane burns in air , it oxidizes and forms oxides of carbon and hydrogen, as shown in the following reaction: CH 4 + 2O 2 —> CO 2 + 2H 2 O But, not all oxidation processes that use oxygen involve burning: 1. Elemental iron slowly oxidizes to compounds such as iron (III) oxide, commonly called “rust” 2. Bleaching stains in fabrics 3. Hydrogen peroxide also releases oxygen when it decomposes. B. Reduction A process called “reduction” is the opposite of oxidation, and originally meant the loss of oxygen from a compound. Oxidation and reduction always occur simultaneously. The substance gaining oxygen (or losing electrons) is oxidized, while the substance losing oxygen (or gaining electrons) is reduced. Today, many of these reactions may not even involve oxygen Redox currently says that electrons are transferred between reactants Mg + S Mg 2+ + S 2- Lets look at one element at a time on both sides of the equation and analyze the elements in the following steps: A. consider magnesium first on the left side Is it neutral or charged ? Do you see a + or sign (charge) on the upper right corner of Mg ? NO! So, what is its charge then? Yes, ZERO! It has no charge, therefore, the element is in neutral state. You can also say that it has a zero charge, i.e., Mg 0 ! B. Consider magnesium on the right side now. Is it neutral or charged ? Do you see a + or sign (charge) on the upper right corner of Mg 2+ ? YES!
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So, what is its charge then? +2 Ask yourself what happened to magnesium in terms of its total charge? To answer this question, write down the part of the reaction called half reaction that Magnesium is involved: Mg 0 Mg 2+ Result: magnesium became more positive! In other words, and element becomes more positive ONLY by loosing more negative charges. Lets look at math example: Consider a negative number such as -10. What happen when -10 becomes more positive by +3? -10 + (+3) = -7
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This note was uploaded on 05/11/2008 for the course BIOL 111 taught by Professor Rizzo during the Fall '07 term at Texas A&M.

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OxidationReductionNotes - A. Oxidation Early chemists saw...

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