OxidationreductionPPT学习课件学习课程.pptx

文档介绍：Oxidation and Reduction
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Oxidation-reduction (redox) reactions involve transfer of electrons
Oxidation – loss of electrons
Reduction – gain of electrons
Both half-reactions must happen at the same time
Can be identified through understanding of oxidation numbers
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Oxidation States
Oxidation number assigned to element in molecule based on distribution of electrons in molecule
There are set rules for assigning oxidation numbers
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Chromium gives great example of different oxidation numbers
Different oxidation states of chromium have different colors
Chromium (II) chloride = blue
Chromium (III) chloride = green
Potassium chromate = yellow
Potassium dichromate = orange
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Oxidation
Oxidation  reactions in which the atoms or ions of an element experience an increase in oxidation state
Ex. combustion of metallic sodium in atmosphere of chlorine gas
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Sodium ions and chloride ions made during exothermic reaction form cubic crystal lattice
Sodium cations are ionically bonded to chloride anions
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Formation of sodium ions shows oxidation b/c each sodium atom loses an electron to become sodium ion
Oxidation state represented by putting oxidation number above symbol of atom and ion
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Oxidation state of sodium changed from 0 (elemental state) to +1 (state of the ion)
A species whose oxidation number increases is oxidized
Sodium atom oxidized to sodium ion
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Reduction
Reduction  reactions in which the oxidation state of an element decreases
Ex. Chlorine in reaction with sodium
Each chlorine atom accepts e- and becomes chloride ion
Oxidation state decreases from 0 to -1
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