In Lab 9, students performed acid-base titrations. Redox reactions can also be u

Question

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 + 2H^+ + 2e^- ----> H2C6H6O6          + 0.06V

I3^- + 2e^- ----> 3I^-                                            +0.53V

What is the net redox reaction that occurs? (Use the lowest possible coefficients. Omit states-of-matter from your answer.)

Please be very clear on what the final answer is so I can understand!!. :) I have asked this question twice before and was given an incorrect answer both times, so I am back asking again! I am only allowed one more submission on this question on my homework.Thank you for helping! :))

Explanation / Answer

C6H6O6 + 2H+ + 2e- ------------> H2C6H6O6 ; Ered0 = 0.06 V.........(1)

I3- + 2e- --------> 3I- ; Ered0 = 0.53 V...........(2)

Since E0red of (2) is greater than (1)

Thus, reaction at cathode = reduction reaction = I3- + 2e- --------> 3I- .............(3)

Reaction at anode = oxidation reaction = H2C6H6O6 ------------> C6H6O6 + 2H+ + 2e- ............(4)

Overall balanced reaction: (3) + (4)

I3- + H2C6H6O6 ------------> C6H6O6 + 2H+ + 3I- ; E0cell = 0.53 - 0.06 = 0.47 V

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