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Chemistry Class 12 > Electrochemistry > Flashcards

Electrochemistry Flashcards

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1
Q

Electrolytic/galvanic/voltaic cell is for

A

Converts chemical energy of spontaneous redox rn into electrical energy.

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2
Q

Salt bridge

A

Connects two solutions without mixing them and maintaining electrical neutrality

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3
Q

EMF

A

P.d between 2 electrodes of a cell when no current is drawn from it

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4
Q

Electrode potential

A

Pd between electrode & electrolyte
Or
The potential of electrode when it shows a tendency to undergo oxidation or reduction in its salt sol

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5
Q

Standard electrode potential

A

Electrode potential when conc. of all species is unity

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6
Q

Cell potential

A

Pd between 2 electrodes of a galvanic cell

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7
Q

E(cell) =

A

E(cath) - E(ano)
Same for standard E(cell)

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8
Q

When is reduced form of standard E.P more stable than hydrogen gas?

A

When it is > 0

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9
Q

Which has max and min tendency to get reduced?

A

Flourine & Lithium

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10
Q

Fluorine is a strong ___ and weak ___

A

Oxidizing agent & weak reducing agent

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11
Q

E(Metal(n+)/M) =

A

E°(M(n+)/M) - 2.303RT/nF log[M]/[Mn+]

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12
Q

1 Faraday is

A

96500C

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13
Q

If E° is -ve

A

It is a stronger reducing agent

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14
Q

Oxidation potential

A

Potential of a electrode when it loses e’

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15
Q

Which element will get reduced easily

A

Element with greater oxidation potential

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16
Q

Which will act as cathode or anode?

A

One with higher reduction potential will be cathode

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17
Q

Movement of e’s is from

A

Anode to cathode

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18
Q

E°(cell) in terms of K(c) is

A

E°(cell) = 0.0591/n logK(c)

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19
Q

Work done by a cell

A

W = EMF × nF

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20
Q

Electrical work done by the system is

A

Spontaneous

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21
Q

ΔG =

A

-nFE(cell)

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22
Q

When is a rn spontaneous?

A

ΔG < 0 and E°(cell) > 0

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23
Q

ΔG° =

A

-2.303RT logK(c)

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24
Q

EMF of Cu

A

0.34V

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25
Q

Zn EmF

A

-0.76V

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26
Q

Will H+ or Cu²+ ions get easily reduced?

A

Cu²+

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27
Q

Inert electrodes examples

A

Platinum or gold

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28
Q

What do inert electrodes do

A

Provide surface for oxidation or reduction

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29
Q

dG is ___ and depends on

A

Extensive prop; n

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30
Q

Purification is also known as

A

Electrolytic refining

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31
Q

Impurities present below anode is

A

Anode mud

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32
Q

Na and Mg are produced by

A

Electrolysis of their fused chlorides

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33
Q

Aluminium is produced by

A

Electrolysis of Aluminium Oxide in the presence of cryolite

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34
Q

Products of electrolysis depends on

A

Conc. of electrolyte, nature of electrolyte and electrode

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35
Q

Conductivity depends on

A

Nature of material, temp, pressure

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36
Q

Semiconductors eg

A

Silicon, doped silicon, gallium arsenide

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37
Q

Substances that are electronically conducting

A

Carbon-black, graphite

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38
Q

Substances having low conductivity

A

Glass, ceramics

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39
Q

Superconductors are

A

Having 0 resistivity or infinite conductivity

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40
Q

Metals and alloys at low temperatures behave as

A

Superconductors

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41
Q

Electronic conductance depends on

A

Nature of material
No of valence e’s
Temperature(decreases with rise in temp)

42
Q

Electrolytic solutions depends on

A

Nature of electrolyte added
Size of ions
Nature of solvent & its viscosity
Conc of electrolyte
Temperature(increases)

43
Q

Faraday’s 1st law

A

Amount of chemical reaction which occurs at any electrode during electrolysis by a current is proportional to quantity of electricity passed through the electrolyte

44
Q

Faraday’s 2nd law

A

The amounts of different substances liberated by the same quantity of electricity passing through the electrolyte solution are proportional to their chemical equivalent weights

45
Q

Equivalent weight/mass w =

A

At. mass/no of e’s lost or gained

46
Q

To carry out electrochemical processes such as liberating O2 from aq NaCl, the extra potential applied is

A

Overpotential

47
Q

Products of electrolysis if we use molten NaCl

A

Na+ and Cl2 gas

48
Q

Which product is liberated at anode and cathode for NaCl

A

Na at cathode and Cl at anode

49
Q

During electrolysis of aq NaCl products are liberated at

A

NaOH, Cl & H are the ions
H gets liberated at Cathode and Cl2 at anode

50
Q

If conc H2SO4 is used

A

SO4 2- undergoes oxidation

51
Q

S2O8 is called

A

Persulphate

52
Q

W =

A

ZQ

53
Q

Electrochemical equivalent is

A

Amount of substance deposited when electricity passed is 1C

54
Q

Z =

A

Equivalent mass/96500

55
Q

Weak electrolytes conduct

A

Less

56
Q

When size of ion increase and salvation is more, conductance?

A

Increases

57
Q

Viscosity is more conductance is

A

Less due to less ion movement

58
Q

1/rho =

A

K kappa which is conductivity

59
Q

Unit of K

A

1/(ohm×m) or S/m(siemen)

60
Q

1/R =

A

G conductance

61
Q

K =

A

GL/A

62
Q

Conductivity

A

The conductance of ions present in unit volume of electrolytic solution

63
Q

Cell constant

A

L/A denoted by G*
G* = R×K

64
Q

Upon dilution conductivity

A

Decreases since no of ions present in unit volume decreases

65
Q

Molar conductivity

A

Conductance of ions in 1 mole of electrolyte dissolved in V volume of the solution kept between electrodes which which are unit distance apart and have area large enough to accommodate 1 mole of electrolyte

66
Q

Λm =

A

K/C = KV where C is conc of solution

67
Q

When volume increases conc

A

Decreases

68
Q

On dilution, molar conductivity

A

Increases even though conductivity decreases

69
Q

Unit of Λm

A

m²/(ohm mol)

70
Q

Limiting molar conductivity is

A

Molar conductivity at max dilution

71
Q

For strong and weak electrolytes, molar conductivity

A

Increases since no of ions increases and degree of dissociation increases

72
Q

Debye Huckel Onsager equation for strong electrolytes

A

Λm = Λ°m - AC^½

73
Q

When conc increases, Λm

A

Decreases

74
Q

Λ°m can be found out for strong electrolyte using

A

graph of debye equation as y=mx+c

75
Q

Kohlrausch’s law of independent migration

A

Limiting molar conductivity of an electrolyte is the sum of limiting molar conductivity of anion & cation in the sol

76
Q

Kohlrausch’s law applications

A

To find Λ°m of weak electrolytes
To find degree of dissociation
To find equilibrium constant

77
Q

Degree of dissociation in terms of Λm

A

Alpha = Λm/Λ°m

78
Q

Primary battery eg

A

Dry/leclanche cell & mercury cell

79
Q

Secondary battery eg

A

Lead storage & Ni-Cd

80
Q

Describe leclanche cell

A

Zn as anode, graphite rod as cathode, graphite rod surrounded by MnO2 & powdered C which undergoes reduction, paste of NH4Cl is electrolyte
1.5V supply

81
Q

Leclanche cell rns

A

Cathode: 2MnO2 + (2NH4+) + 2e –> 2MnO(OH) + 2NH3
Anode: Zn –> (Zn²+) + 2e
Net: you can write
Rn does not stop

82
Q

Describe Mercury cell

A

Zn as anode, HgO as cathode, KOH as electrolyte, Carbon rod is surrounded by paste of HgO & KOH
1.3V supply

83
Q

Mercury cell rns

A

Anode: Zn –> ZnO + 2e
Balanced: Zn + 2OH –> ZnO + H2O + 2e
Cathode: HgO + 2e –> Hg
Balanced: H2O + HgO + 2e –> Hg + 2OH
Net: you can write

84
Q

Describe lead storage

A

Pb grids filled with Pb as anode, Pb grids with PbO2 as cathode, 38% H2SO4 as electrolyte
2v supply

85
Q

Lead storage rns

A

Anode: Pb + SO4 –> PbSO4 + 2e
Cathode: PbO2 + SO4 + H + 2e –> PbSO4 + H2O
Balanced: PbO2 + SO4 + 4H +2e –> PbSO4 + 2H2O
Net: Pb + PbO2 + 2H2SO4 –> 2PbSO4 + 2H2O

86
Q

Describe Ni-Cd cell

A

Cd as anode, NiO2 as cathode, KOH as electrolyte
1.2V supply

87
Q

Cd-Ni rns

A

Anode: 2OH + cd –> Cd(OH)2 + 2e +2H2O
Cathode: NiO2 + 2H2O + 2e –> Ni(OH)2 + 2OH
Net: you can write

88
Q

Hydrogen oxygen fuel cell rns

A

Anode: h2 -> h2O + 2e
Balanced: h2 + 2OH -> 2h2O + 2e
Cathode: O2 -> 2H2O
Balanced: O2 + 4e + 2H2O -> 4OH
Net: you can write

89
Q

Which cell is used most? Why?

A

Hydrogen-oxy fuel cell as it is eco-friendly with no harmful emissions

90
Q

Rusting of iron

A

Anode: 2Fe –> 2Fe + 4e
H2O + CO2 -> H2CO3
Cathode: O2 + 4H + 4e -> 2H2O
Fe²+ + O2 + H2O -> Fe2O3 + H+

91
Q

What is rust

A

Hydrated ferric oxide

92
Q

List two advantages of cadmium cell over lead storage battery

A

Cadmium cell has a longer life cycle and performes good at low temperatures as compared to lead storage cells.
It can operate practically at its full rated capacity at high discharge rates.

93
Q

Application Nickel-Cadmium storage cell

A

Portable power tools, photographic equipment, flashlights

94
Q

Which is +ve and -ve in electrolytic cell?

A

Anode is +ve & cathode is -ve

95
Q

When E(ext) > 1.1V

A

Rn in backwards

96
Q

By 2nd law W1/W2 =

A

E1/E2

97
Q

Uses of electrochemical cell

A

finding pH of solns, find solubility product, find eq. const, get thermodynamic properties

98
Q

A: E(cell) is an intensive parameter but ΔG is an extensive prop
R: Its value depends on n

A

A

99
Q

A substance is a good reducing agent if

A

it’s oxidation potential is more

100
Q

Atm to pascal conversion

A

multiply by 1.01×10⁵PA

Chemistry Class 12 (10 decks)

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