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 | → | 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.)
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(b) What is the stoichiometry of H2C6H6O6 to I3–?
[removed]3:1 [removed]8:3 [removed]2:1 [removed]1:1 [removed]1:2 [removed]3:8 [removed]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 | 83.44 mL | |
mass lemon juice | 84.94 g | |
equivalence volume of I3– | 14.93 mL | |
mmol of I3– |
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mmol of H2C6H6O6 |
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mass of H2C6H6O6 |
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Determine the errors (if any) with each galvanic cell set-up when the anode is on the left. (Select all that apply.)
[removed]There is nothing wrong with this diagram. [removed]The electrodes are in the wrong solution. [removed]The electrons are traveling the wrong direction down the wire. [removed]The salt bridge ions are migrating to the incorrect electrode. [removed]The electrons are traveling through the salt bridge. [removed]The electrodes and solutions are in the wrong compartment.
[removed]There is nothing wrong with this diagram. [removed]The electrodes are in the wrong solution. [removed]The electrons are traveling the wrong direction down the wire. [removed]The salt bridge ions are migrating to the incorrect electrode. [removed]The electrons are traveling through the salt bridge. [removed]The electrodes and solutions are in the wrong compartment.
[removed]There is nothing wrong with this diagram. [removed]The electrodes are in the wrong solution. [removed]The electrons are traveling the wrong direction down the wire. [removed]The salt bridge ions are migrating to the incorrect electrode. [removed]The electrons are traveling through the salt bridge. [removed]The electrodes and solutions are in the wrong compartment.
[removed]There is nothing wrong with this diagram. [removed]The electrodes are in the wrong solution. [removed]The electrons are traveling the wrong direction down the wire. [removed]The salt bridge ions are migrating to the incorrect electrode. [removed]The electrons are traveling through the salt bridge. [removed]The electrodes and solutions are in the wrong compartment.
[removed]There is nothing wrong with this diagram. [removed]The electrodes are in the wrong solution. [removed]The electrons are traveling the wrong direction down the wire. [removed]The salt bridge ions are migrating to the incorrect electrode. [removed]The electrons are traveling through the salt bridge. [removed]The electrodes and solutions are in the wrong compartment.
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.
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Mg → Mg2+ + 2e1-
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Correct.
(b) Write the half-reaction for your strongest oxidizing agent.
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MnO4– + 8H+ + 5e– → Mn2+ +4H2O
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Correct.
(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 and the reduction half-reaction must be multiplied by
(d) Write the net redox reaction.
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Assemble a battery, represented by the diagram below with the cathode in compartment A, with Sn2+/Sn and Cu2+/Cu couples in which the voltage reads positive. (Use the . Use the lowest possible coefficients. Omit states-of-matter from your answer.)
(a) What half-reaction occurs in compartment A?
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Sn → Sn2+ +2e–
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Your answer contains an ambiguous or incomplete reaction equation. Check all the components on the reactant-side of the equation. Check all the components on the product-side of the equation.
(b) What half-reaction occurs in compartment B?
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Cu2+ +2e– → Cu
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Your answer contains an ambiguous or incomplete reaction equation. Check all the components on the reactant-side of the equation. Check all the components on the product-side of the equation.
(c) Write the net redox reaction.
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Sn + Cu2+ → Sn2+ + Cu
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Correct.
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