4 For each of the following electrochemical cells i Identify

4. For each of the following electrochemical cells: i. Identify the anode, the cathode, the reduced species and the oxidized species. ii. Write the half reactions for the anode and cathode, and the net reaction. ii. Calculate the standard cell potential (E°). *Note- For learning purposes, the cathodes are not always on the left! e. C)SO (),H\'(H2S03(a)Co\"(a)Co)

Solution

a.

Cathode : Cr2+/Cr

Anode : Sn/Sn2+

Oxidized : Sn

Reduced : Cr2+

half-reactions,

Sn --> Sn2+ + 2e-

Cr2+ + 2e- --> Cr

net reaction : Sn + Cr2+ --> Sn2+ + Cr

Eo = Ecathode - Eanode = -0.14 - (-0.91) = 0.77 V

b.

Cathode : Ni2+/Ni

Anode : Fe/Fe2+

Oxidized : Fe

Reduced : Ni2+

half-reactions,

Fe --> Fe2+ + 2e-

Ni2+ + 2e- --> Ni

net reaction : Fe + Ni2+ --> Fe2+ + Ni

Eo = Ecathode - Eanode = -0.25 - (-0.44) = 0.19 V

c.

Cathode : Cu2+/Cu

Anode : Pb/Pb2+

Oxidized : Pb

Reduced : Cu2+

half-reactions,

Pb --> Pb2+ + 2e-

Cu2+ + 2e- --> Cu

net reaction : Pb + Cu2+ --> Pb2+ + Cu

Eo = Ecathode - Eanode = 0.337 - 0.126 = 0.211 V

d.

Cathode : Cl2/Cl-

Anode : Zn/Zn2+

Oxidized : Zn

Reduced : Cl2

half-reactions,

Zn --> Zn2+ + 2e-

Cl2 + 2e- --> 2Cl-

net reaction : Zn + Cl2 --> Zn2+ + 2Cl-

Eo = Ecathode - Eanode = 1.358 - (-0.763) = 2.121 V

e.

Cathode : SO4^2-/H2SO3

Anode : Co/Co2+

Oxidized : Co

Reduced : SO4^2-

half-reactions,

Co --> Co2+ + 2e-

SO4^2- + 4H+ + 2e- --> H2SO3 + H2O

net reaction : 2Co + SO4^2- + 4H+ --> 2Co2+ + H2SO3 + H2O

Eo = Ecathode - Eanode = 0.17 - (-0.28) = 0.45 V

f.

Cathode : O2/H2O2

Anode : Cu2+/Cu

Oxidized : Cu

Reduced : O2

half-reactions,

Cu --> Cu2+ + 2e-

O2 + 2H+ + 2e- --> H2O2

net reaction : Cu + O2 + 2H+ --> Cu2+ + H2O2

Eo = Ecathode - Eanode = 0.682 - 0.337 = 0.345 V

g.

Cathode : Cr2O7^2-/Cr3+

Anode : Fe2+/Fe3+

Oxidized : Fe2+

Reduced : Cr2O7^2-

half-reactions,

Fe --> Fe2+ + 2e-

Cr2O7^2- + 14H+ 6e- --> 2Cr3+ + 7H2O

net reaction : 6Fe + Cr2O7^2- + 14H+ 6e- --> 6Fe2+ + 2Cr3+ + 7H2O

Eo = Ecathode - Eanode = 1.33 - 0.771 = 0.559 V