Rules for assigning oxidation numbersstates 1 the

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Rules For Assigning Oxidation Numbers/States 1) The oxidation number of a free (uncombined) element = 0 2) The sum of the oxidation numbers of all atoms in a neutral molecule or formula unit = 0 3) The sum of the oxidation numbers of an polyatomic ion = charge on ion 4) Alkali metals (Group 1A): oxidation number = +1 5) Alkaline earth metals (Group 2A): oxidation number = +2 6) Hydrogen: oxidation number = +1 except when H forms a binary compound with a metal (metal hydride), in which case H has an oxidation number of -1 7) Fluorine: oxidation number = -1 8) Oxygen: oxidation number = -2, except in peroxides (O 2 2- ), in which case the oxidation number of the O = -1 9) In binary compounds with metals: Group 7A – oxidation number = -1 Group 6A – oxidation number = -2 Group 5A – oxidation number = -3
The oxidation numbers/states of elements in their compounds
Examples: Na, Be, K, Pb, H 2 , O 2 , P 4 , S 8 = 0 Examples: Li + , +1 ; Fe 3+ , +3 ; O 2- , -2
NaIO 3 Na = +1 O = -2 3x( -2 ) + 1 + ? = 0 I = +5 IF 7 F = -1 7x( -1 ) + ? = 0 I = +7 K 2 Cr 2 O 7 O = -2 K = +1 7x( -2 ) + 2x( +1 ) + 2x( ?) = 0 Cr = +6 Oxidation numbers of all the elements in the following ?
HCO 3 - O = -2 H = +1 3x( -2) + 1 + ? = -1 C = +4 Oxidation numbers of all the elements in HCO 3 - ?
More oxidation number problems: 0 -1 -3
Zn ( s ) + Cu 2+ ( aq ) Zn 2+ ( aq ) + Cu ( s ) Zn is oxidized Zn Zn 2+ + 2e - Cu 2+ is reduced Cu 2+ + 2e - Cu Zn is the reducing agent Cu 2+ is the oxidizing agent
Types of Oxidation-Reduction Reactions Combination Reaction 2Al + 3Br 2 2AlBr 3 Decomposition Reaction 2KClO 3 2KCl + 3O 2 0 0 +3 -1 +1 +5 -2 +1 -1 0
Types of Oxidation-Reduction Reactions Combustion Reaction S + O 2 SO 2 0 0 +4 -2 2Mg + O 2 2MgO 0 0 +2 -2
Displacement Reaction Ca + 2H 2 O Ca(OH) 2 + H 2 TiCl 4 + 2Mg Ti + 2MgCl 2 Cl 2 + 2KBr 2KCl + Br 2 Hydrogen Displacement Metal Displacement Halogen Displacement Types of Oxidation-Reduction Reactions 0 +1 +2 0 0 +4 0 +2 0 -1 -1 0
Disproportionation Reaction Cl 2 + 2OH - ClO - + Cl - + H 2 O Element is simultaneously oxidized and reduced. Types of Oxidation-Reduction Reactions 0 +1 -1
Ca 2+ (aq) + CO 3 2- (aq) CaCO 3(s) NH 3(aq) + HCl (aq) NH 4 + (aq) + Cl - (aq) Zn (aq) + 2HCl (aq) ZnCl 2(aq) + H 2(g) Ca (s) + F 2(g) CaF 2(s) Precipitation Acid-Base Redox (H 2 Displacement) Redox (Combination) Classify the following reactions.
Gas-forming aqueous reactions carbonates (base) reacting with acids: CaCO 3 (s) + 2HCl(aq) CaCl 2 (aq) + H 2 O(l) + CO 2 (g) This is an acid-base reaction – the net ionic equation is: CO 3 2- (aq) + 2H + (aq) CO 2 (g) + H 2 O(l) metals reacting with water or acids (depending on the metal): Ca(s) + 2H 2 O(l) Ca(OH) 2 (aq) + H 2 (g) This is a redox reaction – Ca is oxidized; H is reduced

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