Homework 12 - ycs73 – Homework 12 – Fakhreddine...

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Unformatted text preview: ycs73 – Homework 12 – Fakhreddine – (53605) 1 This print-out should have 25 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 (part 1 of 4) 10.0 points The redox reaction H + (aq) + Cr 2 O 2 − 7 (aq) + C 2 H 5 OH(aq) → Cr 3+ (aq) + C 2 H 4 O(aq) + H 2 O( ℓ ) is used in acidic solution in the Breatha- lyzer test to determine the level of alcohol in the blood. Which elements are undergoing changes in the oxidation state? 1. Cr and H only 2. None of these 3. O and H only 4. Cr and C only correct Explanation: Cr is reduced from +6 to +3; C is oxidized from- 2 to- 1. 002 (part 2 of 4) 10.0 points What is the initial oxidation number for C? 1. +3 2.- 1 3. 7+ 4.- 2 correct 5. +6 Explanation: 003 (part 3 of 4) 10.0 points What is the coefficient of H + in its balanced reduction half-reaction? Correct answer: 14. Explanation: Oxidation half-reaction: C 2 O 5 OH(aq) → C 2 H 4 O(aq) + 2 H + (aq) + 2 e − Reduction half-reaction: Cr 2 O 2 − 7 (aq) + 14 H + (aq) + 6 e − → 2 Cr 3+ (aq) + 7 H 2 O( ℓ ) 004 (part 4 of 4) 10.0 points What is the coefficient of C 2 H 4 O in the bal- anced redox reaction? Correct answer: 3. Explanation: Balance the e − : 3 [C 2 O 5 OH(aq) → C 2 H 4 O(aq) + 2 H + (aq) + 2 e − ] Cr 2 O 2 − 7 (aq) + 14 H + (aq) + 6 e − → 2 Cr 3+ (aq) + 7 H 2 O( ℓ ) Add the half-reactions: 8 H + (aq) + Cr 2 O 2 − 7 (aq) + 3 C 2 H 5 OH(aq) → 2 Cr 3+ (aq) + 3 C 2 H 4 O(aq) + 7 H 2 O( ℓ ) 005 (part 1 of 2) 10.0 points Using oxidation and reduction half-reactions, balance the skeletal equation Cl 2 O 7 (g) + H 2 O 2 (aq) → ClO − 2 (aq) + O 2 (g) of the production of chlorite ions from dichlo- rine heptoxide. The reaction takes place in a basic solution. What is the smallest possible integer coef- ficient of O 2 in the combined balanced equa- tion? Correct answer: 4. Explanation: Reduction half reaction: Balance O: Cl 2 O 7 (g) → 2 ClO − 2 (aq) + 3 H 2 O( ℓ ) Balance H: Cl 2 O 7 (g) + 6 H 2 O( ℓ ) → 2 ClO − 2 (aq) + 3 H 2 O( ℓ ) + 6 OH − (aq) Balance charge: Cl 2 O 7 (g) + 3 H 2 O( ℓ ) + 8 e − → 2 ClO − 2 (aq) + 6 OH − (aq) Oxidation half reaction: Balance O: H 2 O 2 (aq) → O 2 (g) Balance H: H 2 O 2 (aq) + 2 OH − (aq) → O 2 (g) + 2 H 2 O( ℓ ) ycs73 – Homework 12 – Fakhreddine – (53605) 2 Balance charge: H 2 O 2 (aq) + 2 OH − (aq) → O 2 (g) + 2 H 2 O( ℓ ) + 2 e − Balance the e − : Cl 2 O 7 (g) + 3 H 2 O( ℓ ) + 8 e − → 2 ClO − 2 (aq) + 6 OH − (aq) 4 [H 2 O 2 (aq) + 2 OH − (aq) → O 2 (g) + 2 H 2 O( ℓ ) + 2 e − ] Add the half reactions: Cl 2 O 7 (g) + 4 H 2 O 2 (aq) + 2 OH − (aq) → 2 ClO − 2 (aq) + 4 O 2 (g) + 5 H 2 O( ℓ ) 006 (part 2 of 2) 10.0 points What is the reducing agent in this reaction?What is the reducing agent in this reaction?...
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This note was uploaded on 04/15/2009 for the course CH 53625 taught by Professor Fakhreddine during the Spring '09 term at University of Texas.

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Homework 12 - ycs73 – Homework 12 – Fakhreddine...

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