acid-base titrations

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.)

(b) What is the stoichiometry of H₂C₆H₆O₆ to I₃^–?

(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 Tabe 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–	[removed]mmol
mmol of H2C6H6O6	[removed]mmol
mass of H2C6H6O6	[removed]mg

 

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.

Mg  →  Mg²⁺ + 2e^1-

(b) Write the half-reaction for your strongest oxidizing agent

MnO₄^– + 8H⁺ + 5e^–  →  Mn²⁺ +4H₂O

[removed]

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

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?

Sn  →  Sn²⁺ +2e^–

(b) What half-reaction occurs in compartment B?

Cu²⁺ +2e^–  →  Cu

(c) Write the net redox reaction.

Sn + Cu²⁺  →  Sn²⁺ + Cu