Electrochemistry

Question 1

Examples of primary cell

Answer 1

Dry cell [leclanche cell] ,Hg-cell

Question 2

Examples of secondary cells

Answer 2

Lead storage battery, Ni-Cd cell

Question 3

Dry cell other name

Answer 3

Leclanche cell

Question 4

Dry cell anode

Answer 4

Zn container

Question 5

Dry cell cathode

Answer 5

MnO₂ with Carbon powder

Question 6

Dry cell electrolyte

Answer 6

NH4Cl and ZnCl

Question 7

Dry cell voltage

Answer 7

1.35v to 1.5v

Question 8

Dry cell reaction at anode

Answer 8

Zn —> Zn2+ + 2e-

Question 9

Dry cell reaction at cathode

Answer 9

MnO2 + NH4+ + 1e- —> MnO(OH) + NH3

Question 10

How is cell leakage caused in dry cell

Answer 10

Zn and NH3 produced by the cell reaction combine together to form [ Zn (NH3)4 ] 2+, which is highly acidic and may corrode the reaction vessel and produce a hole in it. This hole is responsible for cell leakage

Question 11

Hg-cell anode

Answer 11

Zn Amalgam

Question 12

Hg-cell Cathode

Answer 12

Mercuric Oxide with Carbon Powder

Question 13

Hg-cell Electrolyte

Answer 13

A paste of ZnO & KOH

Question 14

Hg-cell at anode

Answer 14

Zn (Hg) + 2OH- —> ZnO(s) + H2O + 2e-

Question 15

Hg-cell At cathode

Answer 15

HgO(s) + H2O + 2e- —> Hg + 2OH

Question 16

Hg-cell Net cell reaction

Answer 16

Zn(Hg) + HgO —> ZnO + Hg

Question 17

Pb-storage battery Anode

Answer 17

Metallic grid filled with pure Pb

Question 18

Pb-storage battery cathode

Answer 18

Metallic grid filled with PbO2 (lead dioxide)

Question 19

Pb-storage battery electrolyte

Answer 19

H2SO4 with 38% by mass

Question 20

Pb-storage battery voltage

Answer 20

For a cell it is 2V, For a battery, it is 12V

Question 21

Pb-storage battery at anode

Answer 21

Pb + SO4²- —> PbSO4 + 2e-

Question 22

Pb-storage battery at cathode

Answer 22

PbO2 + SO4²- + 4H+ + 2e- —> PbSO4 + 2H2O

Question 23

Pb-storage battery net cell reaction: (discharge)

Answer 23

Pb + PbO2 + 2H2SO4 —> 2PbSO4 + 2H2O

Question 24

Pb-storage battery Rechargeable Process

Answer 24

2PbSO4 + 2H2O —> Pb + PbO2 + 2H2SO4

Question 25

Ni-Cd Cell overall cell reaction (discharge)

Answer 25

Cd(s) +2Ni(OH)3(s) ---> CdO(s) + 2Ni(OH)2 + H2O

Question 26

Ni-Cd cell anode

Answer 26

Cd metal

Question 27

Ni-Cd cell cathode

Answer 27

Nickel oxide hydroxide

Question 28

Fuel cell definition

Answer 28

Cell in which electrical energy is produced by burning of fuel

Question 29

Fuel cell advantages

Answer 29

*High efficiency (theoretically 100% & practically 70-75%) *Pollution-free working *Continuous source of energy

Question 30

Ni-Cd cell disadvantages

Answer 30

*High temp required *High cost to manufacture

Question 31

Fuel cell definition

Answer 31

Carbon electrodes with suitable catalyst act as anode cathode (catalyst : finely divided Pt or Pd)

Question 32

Fuel cell electrolyte

Answer 32

Aqueous solution of Na or K hydroxide act as electrolyte

Question 33

Fuel cell at anode

Answer 33

2H2 + 4OH- ---> 4H2O + 4E-

Question 34

Fuel cell at cathode

Answer 34

O2 + 2H2O + 4E- ---> 4OH-

Question 35

Fuel cell net cell reaction /overall reaction

Answer 35

2H2 + O2 ---> 2H2O

Question 36

Corrosion definition

Answer 36

Slow destruction of metal due to the attack of atmospheric gases and moisture

Question 37

Fe corrosion anode

Answer 37

Pure iron

Question 38

Fe corrosion cathode

Answer 38

Impure iron

Question 39

Fe corrosion at anodea

Answer 39

Fe ---> Fe²+ + 2e-

Question 40

Fe corrosion at cathode

Answer 40

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

Question 41

1. Standard Hydrogen Electrode (SHE)

Answer 41

[Pt ; H2 /H+]

Question 42

2. Ag - AgCl Electrode

Answer 42

[Pt ; Ag /AgCl /Cl-]

Question 43

Calomel Electrode

Answer 43

[Pt ; Hg /Hg2Cl2 /Cl-]