Chapter 4B TAVSS

Chapter 4B TAVSS - CHEM 161-2007 CHAPTER 4B - CHEMICAL...

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CHEM 161-2007 CHAPTER 4B - CHEMICAL REACTIONS IN AQUEOUS SOLUTIONS PRACTICE PROBLEMS DR. ED TAVSS Oxidation-Reduction Rxns
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Oxidation-Reduction Rxns 46 Chem 161-2006 Final Exam Chapter 4 – Chemical Reactions in Aqueous Solutions Oxidation-Reduction Reactions In the reaction 5H + (aq) + 4CrO 4 2- (aq) + 3CH 3 OH(aq) → 2Cr 2 O 3 (s) + 3HCOO - (aq) + 7H 2 O( l ), identify the reducing agent. A. CrO 4 2- B . CH 3 OH C. Cr 2 O 3 D. HCOO - E. H + +1 +6 -2 -2 -2 +1 +3 -2 +1 +2 -2 +1 -2 5H + (aq) + 4CrO 4 2- (aq) + 3CH 3 OH(aq) → 2Cr 2 O 3 (s) + 3HCOO - (aq) + 7H 2 O( l ) +6 -8 -2 -2 +4 +6 -6 +1 +2 -4 +2 -2 A reducing agent is oxidized. Oxidation is an increase in oxidation number (OXION). Carbon went from -2 in the reactant to +2 in the product, so it was oxidized, and the CH 3 OH is the reducing agent. B
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1 Chem 161-2006 Final Exam Chapter 4 – Chemical Reactions in Aqueous Solutions Oxidation-Reduction Reactions Sulfur cannot be further oxidized in which of the following compounds? A. SO 2 B. H 2 SO 3 C. H 2 S 2 D. H 2 S E . H 2 SO 4 The group number is the highest possible oxidation state for any of the main group elements. For sulfur it is +6. A. SO 2 Oxidation state of S: -4 + X = 0; X = +4. B. H 2 SO 3 Oxidation state of S: +2 +X -6 = 0; X = +4 C. H 2 S 2 Oxidation state of S: +2 + 2X = 0; X = -1 D. H 2 S Oxidation state of S: +2 + X = 0; X = -2 E . H 2 SO 4 Oxidation state of S: +2 + X -8 = 0; X = +6 E CHEM 161-2006 EXAM II TYPES OF CHEMICAL REACTIONS AND SOLUTION STOICHIOMETRY OXIDATION-REDUCTION REACTIONS 16. A pill containing iron as Fe 2+ ions, reacts with KMnO 4 , (source of MnO 4 - ), in the reaction: 5Fe 2+ (aq) + MnO 4 - (aq) + 8H + (aq) 5Fe 3+ (aq) + Mn 2+ (aq) + 4H 2 O( ) All the iron in the pill reacts completely with 19.2 mL of 0.0120 M KMnO 4 . Calculate the mass of iron in the pill. (a) 18.2 mg (b) 41.7 mg (c) 36.4 mg (d) 82.8 mg (e) 64.3 mg 5Fe 2+ (aq) + MnO 4 - (aq) + 8H + (aq) 5Fe 3+ (aq) + Mn 2+ (aq) + 4H 2 O( ) ?g 0.0192L 0.0120M Plan: M MnO4- → mol MnO4- → mol Fe2+ → gFe 2+ → mg Fe2+ (0.0120molMnO 4 - /LMnO 4 - ) x (0.0192LMnO 4 - ) x (5molFe 2+ /1molMnO 4 - ) x (55.85gFe 2+ /molFe 2+ ) x (1mg/0.001g) = 64.3 mg Fe 2+
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CHEM 161-2006 EXAM II TYPES OF CHEMICAL REACTIONS AND SOLUTION STOICHIOMETRY OXIDATION-REDUCTION RXNS 3. In the reaction: Cr 2 O 7 2- (aq) + 6I - (aq) + 14H + (aq) 2Cr 3+ (aq) + 3I 2 (aq) + 7H 2 O( ) (a) I gets reduced (b) Cr gets reduced (c) H gets oxidized (d) O gets reduced (e) O gets oxidized +6 -2 -1 +1 +3 0 +1 -2 Cr 2 O 7 2- (aq) + 6I - (aq) + 14H + (aq) 2Cr 3+ (aq) + 3I 2 (aq) + 7H 2 O( ) The oxidation number of Cr gets reduced from +6 to +3, so Cr is reduced. The oxidation number of I gets increased from -1 to 0, so I is oxidized.
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Chapter 4B TAVSS - CHEM 161-2007 CHAPTER 4B - CHEMICAL...

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