1. In Lab, 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.)
(b) What is the stoichiometry of H2C6H6O6 to I3-?
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 83.44 mL
mass lemon juice 84.94 g
equivalence volume of I3- 14.93 mL
Determine the errors (if any) with each galvanic cell set-up when the anode is on the left. (Select all that apply.)
2. 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.
(b) Write the half-reaction for your strongest oxidizing agent.
(c) Note the number of electrons in each half reaction.
3. 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.
4. 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?
(b) What half-reaction occurs in compartment B?
(c) Write the net redox reaction.
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