chem 1.1 chapter 20

Chem 1.1 chapter 20 - Oxidation xidation Reduction Reactions Reduction Reactions Electrochemistry Electrochemistry Chapter 20 Chapter 20 Chapter 4

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Unformatted text preview: Oxidation xidation-- Reduction Reactions Reduction Reactions Electrochemistry Electrochemistry Chapter 20 Chapter 20 Chapter 4, pp. 137 Chapter 4, pp. 137-- 144 144 Sections in Chapter 20: Sections in Chapter 20: 20.1 20.1-- 20.7 and 20.9 20.7 and 20.9 General Chemistry II, Professor Maggie Ciszkowska General Chemistry II, Professor Maggie Ciszkowska • When a metal undergoes corrosion it loses electrons to form cations: Ca( s ) +2 H 3 O + ( aq ) → Ca 2+ ( aq ) + H 2 O( l ) + H 2 ( g ) • Oxidized: atom, molecule, or ion becomes more positively charged. – Oxidation is the loss of electrons . • Reduced: atom, molecule, or ion becomes less positively charged. – Reduction is the gain of electrons. Oxidation Oxidation-- Reduction Reactions Reduction Reactions General Chemistry II, Professor Maggie Ciszkowska General Chemistry II, Professor Maggie Ciszkowska • Oxidation number for an ion : the charge on the ion. • Oxidation number for an atom : the hypothetical charge that atom would have if it was an ion. • Oxidation numbers are assigned by a series of rules: 1. If the atom is in its elemental form , the oxidation number is zero , e.g., Cl 2 , H 2 , P 4 . 2. For a monoatomic ion, the charge on the ion is the oxidation number, e.g., Na + , S 2 − . Oxidation Oxidation-- Reduction Reactions: Reduction Reactions: Oxidation Numbers Oxidation Numbers General Chemistry II, Professor Maggie Ciszkowska General Chemistry II, Professor Maggie Ciszkowska 3. Nonmetal usually have negative oxidation numbers: a) Oxidation number of O is usually –2. Exceptions: • in OF 2 , oxygen +2, fluorine − 1 • in peroxide ion, O 2 2 − (hydrogen peroxide, H 2 O 2 ), has oxygen with an oxidation number of –1. b) Oxidation number of H is usually +1 (when bonded to nonmetals); it is–1 when bonded to metals from the fist and second group, e.g., NaH, MgH 2 . c) The oxidation number of F is –1. Oxidation Oxidation-- Reduction Reactions: Reduction Reactions: Oxidation Numbers Oxidation Numbers General Chemistry II, Professor Maggie Ciszkowska General Chemistry II, Professor Maggie Ciszkowska 4. The sum of the oxidation numbers for the atoms in a neutral molecule is zero , e.g., H 2 O, HNO 3 . 5. The sum of the oxidation numbers for the atoms in a polyatomic ion equals the charge of this ion , e.g ., H 3 O + , NO 3 − , Hg 2 2+ . 6. Elements from Group I usually have +1 oxidation number. 7. Elements from Group II usually have +2 oxidation number. The best way to assign oxidation numbers is from the Lewis structure of a molecule. Oxidation Oxidation-- Reduction Reactions: Reduction Reactions: Oxidation Numbers Oxidation Numbers General Chemistry II, Professor Maggie Ciszkowska General Chemistry II, Professor Maggie Ciszkowska Assign oxidation numbers to all elements in the following molecules: H 2 O CO 2 Na 2 CO 3 SO 4 2 − K 2 Cr 2 O 7 C 3 H 8 Oxidation Oxidation-- Reduction Reactions: Reduction Reactions: Oxidation Numbers Oxidation Numbers General Chemistry II, Professor Maggie Ciszkowska General Chemistry II, Professor Maggie Ciszkowska Assign oxidation numbers to all elements in the following molecules:...
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This note was uploaded on 04/08/2008 for the course CHEM 1.1 taught by Professor Ciszkowska during the Spring '08 term at CUNY Brooklyn.

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Chem 1.1 chapter 20 - Oxidation xidation Reduction Reactions Reduction Reactions Electrochemistry Electrochemistry Chapter 20 Chapter 20 Chapter 4

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