Nernst Equation

IMPORTANT

Nernst Equation: Overview

This Topic covers sub-topics such as Electrochemical Series, Nernst's Equation, Displacement Reactions, Reactivity of Metals, Applications of Electrochemical Series, Reactivity of Non-metals and, Displacement of Hydrogen from Water/Acids

Important Questions on Nernst Equation

MEDIUM
IMPORTANT

Given that the standard electrode potentials  (E°) of metals are:

 K+/K=2.93V,Ag+/Ag=0.80V,Cu2+/Cu=0.34V,

 Mg2+/Mg=2.37V,Cr3+/Cr=0.74V,Fe2+/Fe=0.44V.

The increasing order of their reducing power is:

HARD
IMPORTANT

Calculate the standard electrode potential of Ni2+/Ni electrode, if emf of the cell Ni (s)|Ni2+(0.01M)||Cu2+(0.1M)|Cu(s) is 0.059 V.

 [Given: ECu2+/Cuo=+0.34V]

HARD
IMPORTANT

The cell emf and ΔrG° for a cell reaction at 25°C are,

 Zn(s)|Zn2+(0.1M)||Cd2+(0.01M)|Cd ​(s)

 [Given,EZn2+/Zno=0.763V,ECd2+/Cdo=0.403V]

 1​ F=96,500Cmol1,R=8.314JK1mol1.

MEDIUM
IMPORTANT

i The  Ecell° of the electrochemical cell representing the reaction is

2Crs+3Fe2+aq2Cr3+aq+3Fes

ii The Ecell at  25°C when Cr+3=0.1 M and Fe2+=0.01 M will be?

ECr+3Cr°=0.74VEFe+2Fe°=0.44V

HARD
IMPORTANT

The standard reduction potential of   C u 2+ /CuandA g + /Ag  electrodes is 0.337 and 0.799 volt respectively. Construct a galvanic cell using these electrodes so that its standard e.m.f. is positive. For what concentration of   A g + will the e.m.f. of the cell at   25°C be zero if the concentration of   C u 2+  is 0.01 M?

HARD
IMPORTANT

The standard reduction potential for Cu2+/Cu is +0.34V.  Calculate the reduction potential at  pH=14 for the above couple.  Ksp  of  Cu(OH)2  is  1.0×1019.

MEDIUM
IMPORTANT

Two student use same stock solution of ZnSO4 and a solution of CuSO4. The EMF of one cell is 0.03 V higher than the other. The concentration of  CuSO4 in the cell with higher EMF value is 0.5 M. Find out the concentration of CuSO4 in the other cell  2.303RTF=0.06:

HARD
IMPORTANT

Find the equilibrium constant for the reaction,  2Feaq3++3Iaq-2Feaq2++I3(aq)- .  For   Fe 3 + / Fe 2 + and I 3 - 1 / I - 1 , the standard reduction potentials in acidic conditions are 0.77V and 0.54V respectively.

HARD
IMPORTANT

The EMF of a cell corresponding to the reaction:

Zn(s)+2H+(aq)Zn2+aq(0.1  M)+H2(g)  (1  atm.)  is  0.28  volt  at  25°C.

The pH of the solution at the hydrogen electrode?
E Z n 2+ /Zn o =0.76volt; E H + / H 2 o =0

MEDIUM
IMPORTANT

If 6.539×102 g of metallic zinc is added to 100 mL saturated solution of AgCl, then Ag s precipitates in the above reaction.

Ksp AgCl=10-10

(Atomic mass of Zn=65.39)
What is the value of logZn2+Ag+2?

E°Ag=0.80 VE°Zn=-0.76 V

Find the number of moles of Ag formed.

HARD
IMPORTANT

A cell, Ag|A g + C u 2+ |Cu, initially contains 1 M A g +  and 1   MC u 2+ ions.

Calculate the change in the cell potential after the passage of 9.65 A of current for 1 h.

HARD
IMPORTANT

An excess of liquid mercury is added to an acidified solution of   1.0× 10 3 MF e 3+ .  It is found that 5% of   F e 3+  remains at equilibrium at   25°C . Calculate   E H g 2 2 + | Hg e o , assuming that the only reaction that occurs is

  2Hg+2F e 3+ H g 2 2+ +2F e 2+ .

(Given   E F e 3+ | F e 2+ o =0.77V.)

EASY
IMPORTANT

Of the halide ions, the most powerful reducing agent is:

HARD
IMPORTANT

For the reduction of N O 3 ion in an aqueous solution, E° is +0.96V. Values E° for some metal ions are given below

V 2+ (aq)+2 e VE°=1.19V F e 3+ (aq)+3 e FeE°=0.04V A u 3+ (aq)+3 e AuE°=+1.40V H g 2+ (aq)+2 e HgE°=+0.86V

The pair(s) of metals that is (are) oxidized by NO3 in aqueous solution is/are

MEDIUM
IMPORTANT

The standard reduction potential values of three metallic cations, X, Y and Z are 0.52,3.03 and1.18V respectively. The order of reducing power of the corresponding metals is:

MEDIUM
IMPORTANT

Using the Nernst equation, calculate emf of the following cell at 298 K:

Crs  Cr3+0.1 M  Fe2+0.01M Fes

Given that,

ECr3+/Cr=-0.75 VEFe2+/Fe=-0.45 V

2.303RTF=0.0591V

MEDIUM
IMPORTANT

Higher reduction potential increases the reactivity of non-metals.

MEDIUM
IMPORTANT

What is the affect of reduction potential on the reactivity of non-metals?

MEDIUM
IMPORTANT

Which halogen will be more reactive?

Reduction potential of bromine- +1.07V or reduction potential of chlorine- 1.36V.

MEDIUM
IMPORTANT

Give an example of non-metal displacing a non-metal in a chemical reaction.