Conductivity (unit Siemen’s S) is directly proportional toarea of the vessel and the concentration of the solution in itand is inversely proportional to the length of the vesselthen the unit of the constant of proportionality is 
EMF of a cell in terms of reduction potential of its left andright electrodes is 
Ecell = Reduction potential of cathode (right)
– Reduction potential of anode (left)
= Eright – Eleft.
What will be the emf for the given cell 
Pt | H2 (P1) | H+ (aq) | | H2 (P2) | Pt
Oxidation half call:-
The net cell reaction
Which of the following reaction is possible at anode?
O.S. of Cr changes from +3 to +6 by loss of electrons. At anode oxidation takes place.
When the sample of copper with zinc impurity is to be purified by electrolysis, the appropriate electrodes are
Pure metal always deposits at cathode
Which of the following is a redox reaction? 
For a cell reaction involving a two-electron change, thestandard e.m.f. of the cell is found to be 0.295 V at 25ºC. The equilibrium constant of the reaction at 25ºC will be [2003
The equilibrium constant is related to the standard emf of cell by the expression
Standard reduction electrode potentials of three metals A, B& C are respectively + 0.5 V, – 3.0 V & –1.2 V. The reducingpowers of these metals are 
NOTE : The higher the negative value of reduction potential, the more is the reducing power.
Hence B > C > A.
When during electrolysis of a solution of AgNO3 9650coulombs of charge pass through the electroplating bath,the mass of silver deposited on the cathode will be
When 96500 coulomb of electricity is passed through the electroplating bath the amount of Ag deposited = 108g
∴ when 9650 coulomb of electricity is passed deposited Ag.
For the redox reaction :
Zn(s) +Cu2+ (0.1M)→ Zn2+ (1M) + Cu(s) taking place in a cell, is 1.10 volt. Ecell for the cell will be 
Several blocks of magnesium are fixed to the bottom of a ship to 
Magnesium, on account of its lightness, great affinity for oxygen and toughness is used in ship. Being a lighter element, magnesium makes the ship lighter when it is fixed to the bottom of the ship.
In a hydrogen-oxygen fuel cell, combustion of hydrogenoccurs to 
In H2 -O2 fuel cell, the combustion of H2 occurs to create potential difference between the two electrodes
Consider the following Eº values
Under standard conditions the potential for the reaction
Fe3+ + e- → Fe2+ΔG° = -1x Fx0.77
Sn2+ + 2e- → Sn(s)ΔG° = -2 x F(-0.14)
for Sn(s) + 2Fe3+ (aq) → 2Fe2+ (aq) +Sn2+ (aq)
∴ Standard potential for the given reaction
The standard e.m.f. of a cell involving one electron changeis found to be 0.591 V at 25ºC. The equilibrium constant ofthe reaction is (F = 96,500 C mol–1; R = 8.314 JK–1 mol–1) 
The limiting molar conductivities Lº for NaCl, KBr and KClare 126, 152 and 150 S cm2 mol–1 respectively. The Lº forNaBr is 
operating (i) + (ii) - (iii)
= 126 +152 -150 = 128 S cm2 mol-1
In a cell that utilises the reaction Zn(s) + 2H+ (aq) → Zn2++ H2(g) addition of H2SO4 to cathode compartment, will 
The values for Cr, Mn, Fe and Co are – 0.41, + 1.57, + 0.77 and + 1.97V respectively. For which one of these
metals the change in oxidation state from +2 to +3 is easiest? 
The given values show that Cr has maximum oxidation potental, therefore its oxidation will be easiest. (Change the sign to get the oxidation values)
For a spontaneous reaction the DG, equilibrium constant (K) and will be respectively 
NOTE : For spontaneous reaction DG should be negative. Equilibrium constant should be more than one
(ΔG = – 2.303 RT log Kc, If Kc = 1 then ΔG = 0; If Kc < 1
The highest electrical conductivity of the following aqueoussolutions is of 
Thus difluoro acetic acid being strongest acid will furnish maximum number of ions showing highest electrical conductivity. The decreasing acidic strength of the carboxylic acids given is difluoro acetic acid > fluoro acetic acid > chloro acitic acid > acetic acid.
Aluminium oxide may be electrolysed at 1000°C to furnishaluminium metal (At. Mass = 27 amu; 1 Faraday = 96,500Coulombs). The cathode reaction is– Al3+ + 3e- → Al° To prepare 5.12 kg of aluminium metal by this method werequire
1 mole of e– = 1F = 96500 C
27g of Al is deposited by 3 × 96500 C
5120 g of Al will be deposited by
Calculate using appropriate molar conductances of the electrolytes listed above at infinite dilution in H2O
Which of the following chemical reactions depict the oxidizing beahviour of H2SO4?
reaction oxidation number of S is decreasing from + 6 to +4 hence undergoing reduction and for HI oxidation
Number of I is increasing from –1 to 0 hence
underegoing oxidation therefore H2SO4 is acting as oxidising agent.
The molar conductivities and at infinite dilution in water at 25ºC are 91.0 and 426.2 S cm2/mol
respectively. To calculate , the additional value required is
is given by the following equation
Hence is required.
Resistance of a conductivity cell filled with a solution of an electrolyte of concentration 0.1 M is 100 W. The conductivity of this solution is 1.29 S m–1. Resistance of the same cell when filled with 0.2 M of the same solution is 520 W. The molar conductivity of 0.2 M solution of electrolyte will be 
Given, R = 520Ω, C = 0.2 M, μ (molar conductivity) = ?
now cell constant is known.)
The equivalent conductances of two strong electrolytes at infinite dilution in H2O (where ions move freely through a
solution) at 25°C are given below : 
What additional information/ quantity one needs to calculate of an aqueous solution of acetic acid?
NOTE : According to Kohlrausch’s law, molar
conductivity of weak electrolyte acetic acid (CH3COOH) can be calculated as follows:
∴ Value of should also be known for
calculating value of
The cell, Zn | Zn2+ (1 M) || Cu2+ (1 M) | Cu was allowed to be completely discharged at 298 K. The relative
concentration of is 
Ecell = 0; when cell is completely discharged.
Given The potential for the cell Cr|Cr3+ (0.1M)|| Fe2+ (0.01 M)| Fe is 
From the given representation of the cell, Ecell can be found as follows.
Hence option (d) is correct answer.
In a fuel cell methanol is used as fuel and oxygen gas is used as an oxidizer. The reaction is
At 298 K standard Gibb’s energies of formation for CH3OH(l), H2O(l) and and CO2 (g) are –166.2, –237.2 and –394.4 kJ
mol–1 respectively. If standard enthalpy of combustion of methonal is – 726 kJ mol–1, efficiency of the fuel cell will be:
= – 394.4 + 2 (–237.2) – (–166.2) – 0
= – 394.4 – 474.4 + 166.2 = – 702.6 k J
% efficiency =
The value of standard electrode potential for the change, Fe3+ (aq) + e– →Fe2+ (aq) will be:
we have to calculate
Fe3+ + e– → Fe2+ … (iii)
As we know that ΔG = –nFE
Thus for reaction (iii)
ΔG = ΔG1 - ΔG ; – nFE° = – nFE1 – (–nFE2)
–nFE° = nFE2 – nFE1
–1FE° = 2× 0.439F – 3 × 0.036 F
–1 FE° = 0.770 F ∴ E° = – 0.770V
The Gibbs energy for the decomposition of Al2O3 at 500°C is as follows :
The potential difference needed for electrolytic reductionof Al2O3 at 500°C is at least 
The correct order of values with negative sign for the four successive elements Cr, Mn, Fe and Co is 
The value of for given metal ions are
The correct order of values without
considering negative sign would be
Mn2+ > Cr2+ > Fe2+ > Co2+.
The reduction potential of hydrogen half-cell will be negative if :
Now if = 2 atm and [H+] = 1M
The standard reduction potentials for Zn2+/Zn, Ni2+/Ni and Fe2+/Fe are –0.76,–0.23 and –0.44 V respectively.
The reaction X+Y2+ →X2++Y will be spontaneous when :
For a spontaneous reaction DG must be –ve
Since ΔG = – nFE°
Hence for ΔG to be -ve ΔE° has to be positive. Which is possible when X = Zn, Y = Ni
Zn + Ni++ → Zn++ + Ni
Based on the data given above, strongest oxidising agentwill be : [JEE M 2013]
higher the value of standard reduction potential
stronger will be the oxidising agent, hence is the strongest oxidising agent.
Resistance of 0.2 M solution of an electrolyte is 50 Ω.The specific conductance of the solution is 1.4 S m–1.The resistance of 0.5 M solution of the same electrolyte is 280 Ω. The molar conductivity of 0.5 M solution of the electrolyte in S m2 mol–1 is:
[JEE M 2014]
Given for 0.2 M solution
For 0.5 M solution
R = 280 Ω; k = ?
= 5 S cm2 mol–1 = 5 × 10–4 S m2 mol–1