ECHE 789B/Spring 2002

Problem Set #2

Due: Thursday January 31

1.  Calculate the half cell potential of the hydrogen electrode in a solution of pH=5, 6, 7,8 and 9 and at partial pressure of hydrogen of 0.5 and 0.8 atm, respectively at 25 o. Cell notation: Pt/H2/H+. Plot the half cell potential as a function of pH at above partial pressures of hydrogen.

2.  Calculate the EMF of the following cell @ 25oC”

O2 (760 mm Hg), Pt;H2O:O2 (76 mm Hg),Pt

O2 (760 mm Hg), Pt;H2O:O2 (100 mm Hg),Pt

O2 (760 mm Hg), Pt;H2O:O2 (200 mm Hg),Pt

O2 (760 mm Hg), Pt;H2O:O2 (300mm Hg),Pt

O2 (760 mm Hg), Pt;H2O:O2 (400 mm Hg),Pt

O2 (760 mm Hg), Pt;H2O:O2 (500 mm Hg),Pt

O2 (760 mm Hg), Pt;H2O:O2 (600mm Hg),Pt

O2 (760 mm Hg), Pt;H2O:O2 (760mm Hg),Pt

O2 (760 mm Hg), Pt;H2O:O2 (1000 mm Hg),Pt

It is known that in any given differential aeration cell, the electrode in contact with the lower pressure is the anode (for a common electrolyte of the same activity). What is the polarity and which electrode is the anode. Plot the EMF as a function of oxygen pressure a@ 25 oC. Compare the results for 60oC.

3.  The standard potential for oxygen electrode reaction at pH=14

4OH- = O2+ 2H2O + 4e- is E1o OH-/O2 =-0.401 V

Calculate E2o for oxygen electrode reaction @ pH=0:

2H2O = O2+ 4H+ +4e-

Hint: 1. Since both reactions represent oxygen electrode E2-E1=0

2. (H+)(OH-) =Kw = 10-14

4.  Calculate the EMF of a cell made up of a hydrogen electrode (pH2=1 atm) and an oxygen electrode with pO2=0.1; 03;0.5;07 and 1 atm in 0.5 M KOH. Estimate the polarity of the cell and plot the cell potential as a function of the oxygen pressure.

Hint: Assume that the oxygen electrode is reversible.

5. (Devan Sheba) Construct a pH-potential diagram for lead with the following reactions. Activity of all dissolved substances is 10-6. Assume any other reactions.

a). PbH2+Pb=PbO+2H++2e- Eo =-1.507V

b). Pb=Pb2++2e- Eo =-0.126V

c). Pb+H2O=PbO+2H++2e- Eo =0.248V

d). Pb+H2O=HPbO2-+3H++2e- Eo =0.702V

Indicate regions of corrosion, passivity and stability.

5. (Godfrey Sihha) Construct a pH-potential diagram for tin with the following reactions. Activity of all dissolved substances is 10-6. Assume any other reactions.

a). SnH4=Sn+4H++4e- Eo =-1.076V

b). Sn=Sn2++2e- Eo =-0.136V

c). Sn+2H2O=HSnO2-+3H++2e- Eo =0.333V

d). Sn2++2H2O=SnO2+4H++2e- Eo =-0.077V

e). Sn+2H2O=SnO2+4H++4e- Eo =-0.106V

f). HSnO2-=SnO2+H++2e- Eo =-0.546V

Indicate regions of corrosion, passivity and stability.

5. (Hector Colon) Construct a pH-potential diagram for copper when activity of all dissolved substances is 10-6. The reactions given.

a). Cu=Cu++e- Eo =0.520V

b). 2Cu+H2O=Cu2O+2H++2e- Eo =0.471V

c). Cu2O+2H+=2Cu2++H2O+2e- Eo =0.203V

d). Cu2O+H2O=2CuO+2H++2e- Eo =0.669V

Assume any other reactions. Indicate regions of corrosion, passivity and stability.

5. (Leblanc Rene) Construct a pH-potential diagram for cobalt with the following reactions. Activity of all dissolved substances is 10-6. Assume any other reactions.

a). Co=Co2++2e- Eo =-0.282V

b). Co2+=Co3++e- Eo =1.808V

c). HCoO2-+3H+=Co3++2H2O+e- Eo =-0.065V

d). Co+H2O=CoO+2H++2e- Eo =0.095V

e). Co+2H2O=HCoO2-+3H++2e- Eo =0.659V

f). 2Co2++3H2O=Co2O3+6H++2e- Eo =1.746

Indicate regions of corrosion, passivity and stability.

5. Lingyin Liu: Construct a pH-potential diagram for nickel with the following reactions. Activity of all dissolved substances is 10-6. Assume any other reactions.

a). Ni=Ni2++2e- Eo =-0.250V

b). Ni+2H2O=HNiO2-+3H++2e- Eo =0.648V

c). Ni+H2O=NiO+2H++2e- Eo =0.110V

d). 2Ni2++3H2O=Ni2O3+6H++2e- Eo =1.753V

e). 2NiO+H2O=Ni2O3+2H++2e- Eo =1.020V

Indicate regions of corrosion, passivity and stability.

5. Mohtadi Rana: Construct a pH-potential diagram for silver with the following reactions. Activity of all dissolved substances is 10-6. Assume any other reactions.

a). Ag=Ag++e- Eo =0.799V

b). Ag+=Ag2++e- Eo =1.980V

c). 2Ag+H2O=Ag2O+2H++2e- Eo =1.173V

d). Ag++H2O=AgO+2H++e- Eo =1.772V

e). Ag2O+H2O=2AgO+2H++2e- Eo =1.398V

Indicate regions of corrosion, passivity and stability.

5. Ning Gang: Construct a pH-potential diagram for Zinc with the following reactions. Activity of all dissolved substances is 10-6. Assume any other reactions.

a). Zn=Zn2++2e- Eo =-0.763V

b). Zn+H2O=ZnO+2H++2e- Eo =-0.439V

c). Zn+2H2O =HZnO2-+3H++2e- Eo =0.054V

d). Zn+2H2O=ZnO22-+4H++2e- Eo=0.441V

Indicate regions of corrosion, passivity and stability.

5. Ramasammy Ramaraj: Construct a pH-potential diagram for Cd. Activity of all dissolved substances is 10-6. Indicate regions of corrosion, passivity and stability. The Equilibrium reactions and potentials are available in “Atlas of Electrochemical Equilibrium in Aqueous Solutions by Marcel Pourbaix.

5. Sethuram V: Construct a pH-potential diagram for Ti. Activity of all dissolved substances is 10-6. Indicate regions of corrosion, passivity and stability. Equilibrium reactions and potentials are available in “Atlas of Electrochemical Equilibrium in Aqueous Solutions by Marcel Pourbaix.

5. Subramanian Nalini: Construct a pH-potential diagram for Ti. Activity of all dissolved substances is 10-6. Indicate regions of corrosion, passivity and stability. Equilibrium reactions and potentials are available in “Atlas of Electrochemical Equilibrium in Aqueous Solutions by Marcel Pourbaix.

5. Surya Vasudevan: Construct a pH-potential diagram for Pd. Activity of all dissolved substances is 10-6. Indicate regions of corrosion, passivity and stability. Equilibrium reactions and potentials are available in “Atlas of Electrochemical Equilibrium in Aqueous Solutions by Marcel Pourbaix.

5. Swaminatha Prabu: Construct a pH-potential diagram for Ce . Activity of all dissolved substances is 10-6. Indicate regions of corrosion, passivity and stability. Equilibrium reactions and potentials are available in “Atlas of Electrochemical Equilibrium in Aqueous Solutions by Marcel Pourbaix.

5. Wang Wentao: Construct a pH-potential diagram for Mo. Activity of all dissolved substances is 10-6. Indicate regions of corrosion, passivity and stability. Equilibrium reactions and potentials are available in “Atlas of Electrochemical Equilibrium in Aqueous Solutions by Marcel Pourbaix.

5. Zhu Xiaojing: Construct a pH-potential diagram for Mn. Activity of all dissolved substances is 10-6. Indicate regions of corrosion, passivity and stability. Equilibrium reactions and potentials are available in “Atlas of Electrochemical Equilibrium in Aqueous Solutions by Marcel Pourbaix.

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