Preview of “Lab 11 PostLab - Redox Reactions”

Preview of “Lab 11 PostLab - Redox Reactions” - Lab 11...

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Unformatted text preview: 12/5/12 Lab 11 PostLab -‐‑ Redox Reactions Steve Yarush CH102, section 021, Fall 2012 Instructor: Brandon Zoellner WebAssign Lab 11 PostLab -­ Redox Reactions (Postlab) Current Score : 22 / 25 Due : Saturday, November 17 2012 11:00 PM EST The due date for this assignment is past. Your work can be viewed below, but no changes can be made. Important! Before you view the answer key, decide whether or not you plan to request an extension. Your Instructor may not grant you an extension if you have viewed the answer key. Automatic extensions are not granted if you have viewed the answer key. Request Extension 1. 4/4 points | Previous Answers NCSUGenChem102LabV1 11.POST.01. Consider your experimental results from part A of this lab. Suppose your strongest reducing agent were added to your strongest oxidizing agent. (Use the lowest possible coefficients. Omit states-­ of-­matter from your answers.) (a) Write the half-­reaction for your strongest reducing agent. Mg → Mg2+ + 2e1-­ Mg → Mg2+ + 2 e-­ Mg -‐‑-‐‑> Mg^2+ + 2e^1-‐‑ (b) Write the half-­reaction for your strongest oxidizing agent. MnO 1-­ 4 + 8H1+ + 5e1-­ → Mn2+ + 4H2O MnO -­ 4 + 8 H+ + 5 e-­ → Mn2+ + 4 H2O MnO_4^1-‐‑ + 8H^1+ + 5e^1-‐‑ -‐‑-‐‑> Mn^2+ + 4H_2O (c) Note the number of electrons in each half reaction. In order to balance the number of electrons lost and gained, the oxidation half-­ reaction must be multiplied by five, five, and the reduction half-­ reaction must be multiplied by two. two. (d) Write the net redox reaction. 5Mg + 2MnO 1-­ -‐‑Responses/view_key?dep=4450545 1/10 12/5/12 Lab 11 PostLab -‐‑ Redox Reactions 4 + 16H1+ → 5Mg2+ + 2Mn2+ + 8H2O 2 MnO -­ 4 + 5 Mg + 16 H+ → 2 Mn2+ + 8 H2O + 5 Mg2+ 5Mg + 2MnO_4^1-‐‑ + 16H^1+ -‐‑-‐‑> 5Mg^2+ + 2Mn^2+ + 8H_2O Redox Reactions 2. 1/3 points | Previous Answers NCSUGenChem102LabV1 11.POST.02. Students should always be careful of the chemical reaction between jewelry and laboratory reagents. The Standard Reduction Potentials Table shows the reduction reactions and potentials for some common lab reagents and metals. (a) What is the net redox reaction that occurs when Au comes into contact with acidic KMnO4? (Use the lowest possible coefficients. Omit states-­of-­matter from your answer.) 2MnO4-­ + 16H+ + 5Au → 5Au2+ + 2Mn2+ +8H2O 5 Au + 24 H+ + 3 MnO -­ 4 → 5 Au3+ + 3 Mn2+ + 12 H2O 2MnO_4^-‐‑ + 16H^+ + 5Au -‐‑-‐‑> 5Au^2+ + 2Mn^2+ +8H_2O (b) What is E°cell for the reaction? (No Response) 0.01 V (c) Which metal is the most reactive? Ag Au Cu Ni Pt -‐‑Responses/view_key?dep=4450545 2/10 12/5/12 Lab 11 PostLab -‐‑ Redox Reactions (d) Which reagent is the most reactive? Cr 2O72− MnO4− SO42− Redox Reactions 3. 4/4 points | Previous Answers NCSUGenChem102LabV1 11.POST.03. During part B of your lab, you measured electrochemical cell potentials with a Cu2+/Cu couple as the anode. Predict the results you would observe if Zn2+/Zn were the anode. half-­cell predicted potential difference in V Cu2+ /Cu +1.10 1.10 Ag+ /Ag +1.56 1.56 Pb2+ /Pb +0.63 0.63 Zn2+ /Zn 0 0 Redox Reactions 4. 4/4 points | Previous Answers NCSUGenChem102LabV1 11.POST.04. In part B of Lab 11, you measured the voltage of several galvanic cells. Assemble a battery, represented by the diagram below with the cathode in compartment A, with Zn2+/Zn and Fe2+/Fe couples in which the voltage reads positive. (Use the Standard Reduction Potentials Table. Use the lowest possible coefficients. Omit states-­of-­matter from your answer.) -‐‑Responses/view_key?dep=4450545 3/10 12/5/12 Lab 11 PostLab -‐‑ Redox Reactions (a) What half-­reaction occurs in compartment A? Fe2+ + 2e1-­ → Fe Fe2+ + 2 e-­ → Fe Fe^2+ + 2e^1-‐‑ -‐‑-‐‑> Fe (b) What half-­reaction occurs in compartment B? Zn → Zn2+ + 2e-­ Zn → Zn2+ + 2 e-­ Zn -‐‑-‐‑> Zn^2+ + 2e^-‐‑ (c) Write the net redox reaction. Fe2+ + Zn → Fe + Zn2+ Fe2+ + Zn → Fe + Zn2+ Fe^2+ + Zn -‐‑-‐‑> Fe + Zn^2+ (d) What is the cell potential? .32 0.32 V Redox Reactions 5. 4/5 points | Previous Answers NCSUGenChem102LabV1 11.POST.05. Green checks and red X's are not displayed for this question. Determine the errors (if any) with each galvanic cell set-­up when the anode is on the left. (Select all that apply.) -‐‑Responses/view_key?dep=4450545 4/10 12/5/12 Lab 11 PostLab -‐‑ Redox Reactions There is nothing wrong with this diagram. The electrodes are in the wrong solution. The electrons are traveling the wrong direction down the wire. The salt bridge ions are migrating to the incorrect electrode. The electrons are traveling through the salt bridge. The electrodes and solutions are in the wrong compartment. -‐‑Responses/view_key?dep=4450545 5/10 12/5/12 Lab 11 PostLab -‐‑ Redox Reactions There is nothing wrong with this diagram. The electrodes are in the wrong solution. The electrons are traveling the wrong direction down the wire. The salt bridge ions are migrating to the incorrect electrode. The electrons are traveling through the salt bridge. The electrodes and solutions are in the wrong compartment. There is nothing wrong with this diagram. The electrodes are in the wrong solution. The electrons are traveling the wrong direction down the wire. The salt bridge ions are migrating to the incorrect electrode. The electrons are traveling through the salt bridge. The electrodes and solutions are in the wrong compartment. -‐‑Responses/view_key?dep=4450545 6/10 12/5/12 Lab 11 PostLab -‐‑ Redox Reactions There is nothing wrong with this diagram. The electrodes are in the wrong solution. The electrons are traveling the wrong direction down the wire. The salt bridge ions are migrating to the incorrect electrode. The electrons are traveling through the salt bridge. The electrodes and solutions are in the wrong compartment. -‐‑Responses/view_key?dep=4450545 7/10 12/5/12 Lab 11 PostLab -‐‑ Redox Reactions There is nothing wrong with this diagram. The electrodes are in the wrong solution. The electrons are traveling the wrong direction down the wire. The salt bridge ions are migrating to the incorrect electrode. The electrons are traveling through the salt bridge. The electrodes and solutions are in the wrong compartment. Redox Reactions 6. 4.5/4.5 points | Previous Answers NCSUGenChem102LabV1 11.POST.06. In Lab 9, students performed acid-­base titrations. Redox reactions can also be used in titrations. An example is the titration of ascorbic acid (H2C6H6O6) in lemon juice using triiodide (I3– ). A starch indicator will turn the solution blue-­black at the endpoint. The half-­reactions involved are shown below. C6H6O6 + 2 H + + 2 e– → H2C6H6O6 +0.06 V I3– + 2 e– → 3 I – +0.53 V (a) What is the net redox reaction that occurs? (Use the lowest possible coefficients. Omit states-­of-­matter from your answer.) I3-­+H2C6H6O6 → 3I-­ + C6H6O6 + 2H+ H2C6H6O6 + I3-­ → C6H6O6 + 3 I-­ + 2 H+ I_3^-‐‑+H_2C_6H_6O_6 -‐‑-‐‑> 3I^-‐‑ + C_6H_6O_6 + 2H^+ (b) What is the stoichiometry of H2C6H6O6 to I3–? -‐‑Responses/view_key?dep=4450545 8/10 12/5/12 Lab 11 PostLab -‐‑ Redox Reactions 3:1 8:3 2:1 1:1 1:2 3:8 1:3 (c) Use the data given below to determine the amount of ascorbic acid in lemon juice. (Note: The recommended daily allowance of ascorbic acid (Vitamin C) is 90 mg.) Data Table P6: Titration of ascorbic acid in lemon juice with triiodide concentration of I3– 0.0210 M volume lemon juice 76.79 mL mass lemon juice 78.17 g equivalence volume of I3– 17.27 mL mmol of I3– .363 0.363 mmol mmol of H2C6H6O6 .363 0.363 mmol mass of H2C6H6O6 63.9 63.9 mg Redox Reactions -‐‑Responses/view_key?dep=4450545 9/10 12/5/12 Lab 11 PostLab -‐‑ Redox Reactions 7. 0.5/0.5 points | Previous Answers NCSUGenChem102LabV1 11.POST.07. You are now answering the last question of the last Postlab assignment in CH102. Which of the following words or phrases best describes your emotions at this point? YEE-­HAW!!! I am SO outta here! Glory Hallelujah! Aw, nuts. All good things must end. I can't wait for my next chemistry lab course! -‐‑Responses/view_key?dep=4450545 10/10 ...
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