Homework 7-solutions

# Homework 7-solutions - sung (es24394) Homework 7 vanden...

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sung (es24394) – Homework 7 – vanden bout – (51640) 1 This print-out should have 29 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. 001 10.0 points Using the set oF smallest possible integer co- e±cients to balance the redox equation ClO 3 + I 2 IO 3 + Cl (acidic solution), the coe±cient For I 2 is 1. 1. 2. 2. 3. The correct coe±cient is not given. 4. 3. correct 5. 4. Explanation: The oxidation number oF Cl changes From +5 to - 1, so Cl is reduced. The oxidation number oF I changes From 0 to +5, so I is oxidized. We set up oxidation and reduction halF-reactions: Red: ClO 3 Cl Oxid: I 2 IO 3 Cl atoms are balanced. We need 2 IO 3 molecules to balance I: Oxid: I 2 2 IO 3 Since this is an acidic solution, we use H 2 O and H + to balance O and H atoms, adding the H 2 O to the side needing oxygen: Red: 6 H + + ClO 3 Cl + 3 H 2 O Oxid: 6 H 2 O + I 2 2 IO 3 + 12 H + We balance the total charge in each halF- reaction by adding electrons. In the preceding reduction reaction there is a total charge oF +5 on the leFt and - 1 on the right. Six elec- trons are added to the leFt: Red: 6 e + 6 H + + ClO 3 Cl + 3 H 2 O Oxid: 6 H 2 O + I 2 2 IO 3 + 12 H + + 10 e The number oF electrons gained by Cl must equal the number oF electrons lost by I. We multiply the reduction reaction by 5 and the oxidation reaction by 3 to balance the elec- trons: Red: 30 e + 30 H + + 5 ClO 3 5 Cl + 15 H 2 O Oxid: 18 H 2 O + 3 I 2 6 IO 3 + 36 H + + 30 e Adding the halF-reactions gives 18 H 2 O + 3 I 2 + 30 H + + 5 ClO 3 6 IO 3 + 36 H + + 5 Cl + 15 H 2 O Canceling like terms gives the overall bal- anced equation 3 H 2 O + 3 I 2 + 5 ClO 3 6 IO 3 + 6 H + + 5 Cl 002 10.0 points How many electrons are required to balance the halF reaction below? H + + ClO + e -→ Cl + H 2 O 1. 4 2. 1 3. 2 correct 4. 3 Explanation: Each chlorine atom undergoes a change oF oxidation state From +1 to - 1. This is there- Fore a 2 electron process. 003 10.0 points Consider the reaction Zn(s) + OH (aq) + H 2 O( ) + NO 3 (aq) Zn(OH) 2 4 (aq) + NH 3 (g) IF the coe±cient oF NO 3 in the balanced equation is 1, how many electrons are trans- Ferred in the reaction? 1. 6 2. 8 correct 3. 10 4. 2 5. 4 Explanation:

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sung (es24394) – Homework 7 – vanden bout – (51640) 2 004 10.0 points In the reaction 2 MnO 4 + 16 H + + 10 I 2 Mn 2+ + 8 H 2 O + 5 I 2 of permanganate anion with iodide in acidic solution, what has been reduced and what is the change in oxidation number?
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## This note was uploaded on 03/27/2011 for the course CHEM 302 taught by Professor Mccord during the Spring '10 term at University of Texas.

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Homework 7-solutions - sung (es24394) Homework 7 vanden...

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