Electrochemistry

Question 1

Galvanic cell

Answer 1

Spontaneous Chemical rxn energy into electrical energy
Anode half (oxidation) : -ve terminal

Question 2

Salt bridge and it’s functions

Answer 2

Avoid KCl in Salt bridge when Ag2+, Pb2+, Hg2+, Tl+ ions are present.

Conc electrolyte like KCl ,KNO3 etc in NH4NO3. Agar agar

• Completes the circuit
• Maintain electrical neutrality
• Minimises liquid liquid junction potential

Question 3

Reduction potential

Answer 3

Tendency of reduction half cell (Cathode) to get reduced.

Question 4

Nernst equation

Answer 4

Ecell = E°cell -RT/nF (logQ)
Derived from :
 ∆rG= ∆rG° + RTlogQ ; 
∆rG= -nFEcell 
R(298K)/F = 0.059

Question 5

Thermodynamics of galvanic cell

Answer 5

∆S =nF (dE/dT)

E° = -∆H°/nF + T(dE/dT)

Question 6

Oxidation and reduction of water

Answer 6

At cathode(reduction):
2H2O + (2e-) —–> H2 + 2(OH-) E° = -0.828V
At anode(oxidation):
2H2O —–> O2 +(4H+)+(4e-) E°= -1.23V

Question 7

Temperature Vs conductor

Answer 7

Electronic conductor inversely proportional to temperature .

Ionic conductor directly proportional to temperature .

Question 8

Molar conductivity; ∆m

Answer 8

∆m = K*V = K/C =∆eq * n factor

Question 9

Variations of K and ∆m with dilution

Answer 9

K decreases with dilution and ∆m increases with dilution
When strong electrolyte (inter ionic interaction reduces)
∆m = ∆m°° -b√c ( linear relation)
When weak electrolyte ( alpha increases )
No linear relation

Question 10

Relation between ionic mobility and conductivity

Answer 10

Ionic mobility directly proportional to conductivity

Conductivity:
K>grp 2 (except Be2+)>Na>Li

Question 11

Dry cell

Answer 11

Primary cell Also called Leclanche cell used in transistors and clocks. Cell potential is nearly 1.5V. Electrode rxns are complex can be written as
Electrolyte: moist paste of NH4Cl & ZnCl2
Anode(zinc container):
Zn(s)—-> Zn2+ + 2e-
Cathode( graphite rod surrounded by powdered MnO2 and C):
MnO2 + NH4+ + e- —–> MnO(OH) + NH3

Question 12

Mercury cell

Answer 12

Primary cell suitable for low current devices like hearing aids , watches,etc. Cell potential is 1.35V
Electrolyte : a paste of KOH and ZnO
Anode ( zinc mercury amalgam):
Zn(hg) +2OH- -----> ZnO(s) + H2O+2e-
Cathode(paste of HgO & C):
HgO + H2O + 2e- ----> Hg(l) + 2OH-

Question 13

Fuel cell

Answer 13

Galvanic cells designed to convert energy of combustion of fuels like hydrogen, methane, methanol etc directly into electrical energy
They produce electricity with an efficiency of 70% compared to thermal plants white efficiency is 40%