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+ +4eHint: 1. Since both reactions represent oxygen electrode E2-E1=0
2. (H+)(OH-) =Kw = 10-14
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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++2eEo =-1.507V
b). Pb=Pb2++2eEo =-0.126V
+
c). Pb+H2O=PbO+2H +2e
Eo =0.248V
d). Pb+H2O=HPbO2-+3H++2eEo =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++4eEo =-1.076V
b). Sn=Sn2++2eEo =-0.136V
+
c). Sn+2H2O=HSnO2 +3H +2e
Eo =0.333V
d). Sn2++2H2O=SnO2+4H++2eEo =-0.077V
e). Sn+2H2O=SnO2+4H++4eEo =-0.106V
f). HSnO2-=SnO2+H++2eEo =-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++eEo =0.520V
+
b). 2Cu+H2O=Cu2O+2H +2e
Eo =0.471V
c). Cu2O+2H+=2Cu2++H2O+2eEo =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++2eEo =-0.282V
2+
3+ b). Co =Co +e
Eo =1.808V
c). HCoO2-+3H+=Co3++2H2O+eEo =-0.065V
d). Co+H2O=CoO+2H++2eEo =0.095V
e). Co+2H2O=HCoO2-+3H++2eEo =0.659V
2+
+
f). 2Co +3H2O=Co2O3+6H +2e
Eo =1.746
Indicate regions of corrosion, passivity and stability.
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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++2eEo =-0.250V
2+
b). Ni+2H2O=HNiO +3H +2e
Eo =0.648V
c). Ni+H2O=NiO+2H++2eEo =0.110V
d). 2Ni2++3H2O=Ni2O3+6H++2eEo =1.753V
e). 2NiO+H2O=Ni2O3+2H++2eEo =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++eEo =0.799V
+
2+ b). Ag =Ag +e
Eo =1.980V
c). 2Ag+H2O=Ag2O+2H++2eEo =1.173V
+
d). Ag +H2O=AgO+2H++eEo =1.772V
e). Ag2O+H2O=2AgO+2H++2eEo =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++2eEo =-0.763V
+
b). Zn+H2O=ZnO+2H +2e
Eo =-0.439V
c). Zn+2H2O =HZnO2-+3H++2eEo =0.054V
d). Zn+2H2O=ZnO22-+4H++2eEo=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.
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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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