Complexation and Redox Titrations Exercises

Cell potentials & Redox Titrations

  1. What is the potential for the galvanic cell depicted below:


Pt(s) | N2H5+ (2.59 mM), NH4+ (9.01 mM), pH 5.21 || Pb2+ (15.06 mM), pH 4.88 | PbO2(s) | Pb(s)


  1. A galvanic cell, depicted in line notation below, has been prepared to determine the Ka of a weak base. The sodium salt of the base (NaB) is added to the cathode where is reacts with water. The cell potential is measured to be –1.001 V. Determine the Ka for this unknown base, keeping in mind that neither the Na+, B– or BH are redox active.


Pt(s) | I3– (82.10 mM), I– (17.34 mM) || SO32– (45.21 mM), S2O32– (67.20 mM), NaB (16.90 mM)

  1. A solution containing ClO3– is to be analyzed by a redox titration. Which of the titrant options below could effectively reduce ClO3–, through the half reaction scheme below?


 

ClO3– + 2H+ + e– ⇌ ClO2 + H2O E° = 1.130 V


 

 

Titrant

Reduction reaction

E° (V)

Effective (Y/N)?

Mg2+

Mg2+ + 2e ⇌ Mg(s)

–2.022

 

Fe(CN)63–

Fe(CN)63- + e ⇌ Fe(CN)64-

0.356

 

Cr2+

Cr3+ + e ⇌ Cr2+

–0.42

 

Pb4+

Pb4+ + 2e ⇌ Pb2+

1.69

 

Co(s)

Co2+ + 2e ⇌ Co(s)

–0.282

 

 

  1. You have a 40.00 mL solution that contains 25.00 mM perchlorate (ClO4–), buffered to a pH of 3.65. You reduce the perchlorate by titrating it with a solution of 160.0 mM ruthenium(II) (Ru2+). During the course of the titration you record the cell potential using a platinum cathode, and a S.C.E., what potentials will you measure at each of the titration volumes listed below?


 

Total titrant

volume added (mL)

Cell potential (volts)

4.53

 

8.45

 

12.50

 

15.00

 

16.98

 
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