180803146 Electrochemistry PDF

5/28/2018 180803146 Electrochemistry PDF

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ELECTRC!E"#$TR%

'Type the document subtitle(

')ick the date(

Neeraj Kumar


2/35

ELECTRO CHEMISTRY

Sri Chaitanya IIT-JEE Academy, 10-A, Talwandi, Jhalawar Road, Kota- 324005, (Raj). 2

ELECTROCHEMISTRY

1. INTRODUCTION:Electrochemistry is the branch of chemistry which deals with inter conversionof chemical energies and electrical energies. In electrochemistry, we discuss electrolytic reactions

(reactions occurring due to passage of electricity through solutions) as well as electrogenetic

reactions(reactions producing electric energy).

2. ELECTROLYTIC CONDUCTION (ELECTROLYSIS):

(i) Electrolytic conduction is exhibited principally by

molten form and by aqueous solutions of salts or

substances. It takes place due to free movement of

ions.

(ii) Consider electrolytic conduction of molten NaCl

between inert electrodes in electrolytic cells as

shown in figure.

Na+

Cl

NaCl Molten

+

anode

Cathode

DCe

TABLE 1

Phenomenon At cathode At anode

(a) Ions attracted Cations Anions

(b) Direction of movement of

electrons

Into cell Out of cell

(c) Half cell reaction Reduction Oxidation

(Na++ e Na) (Cl Cl2+ e)

(d) Sign Negative, since it is

attached to the negative

end of battery.

Positive, since it is attached

to the positive end of the

battery.

(iii) Within the cell, current is carried by the movements of ions, cations towards the negative electrode

(called the cathode) and anions towards the positive electrode (called the anode). This movement of

ions is called electrolytic conduction.

(iv) Factors, that influence the electrolytic conductivity of solutions of electrolytes are inter ionic

attraction, solvation of ions, viscosity of solvent, etc. and these factors depends on the attraction of

solute solute, solute solvent and solvent solvent respectively.

(v) The average kinetic energy of the solute ions increases as the temperature is raised and, therefore, the

conductance of electrolytic conductors generally increases.

2.1 FARADAYS LAWS OF ELECTROLYSIS:

FIRST LAW:For the same electrolyte, the mass of a substance produced or consumed at an electrode is

directly proportional to the quantity of electricity passed through the electrolytic cell.

W Q

or, W = Z Q = Z .I.t

Where Z = Electrochemical equivalent of the substantce. When I = 1 ampere and t = 1 second, w = Z,so, electrochemical equivalent (ECE) of any substance may be defined as the mass of the substance

produced or consumed when a current of 1 ampere for 1 second (i.e. 1 coulomb) is passed through the

electrolyte.


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ELECTRO CHEMISTRY


SECOND LAW: When same quantity of electricity is passed through different electrolytes, the

amounts of products obtained are proportional to their equivalent weights.

W E

3. ELECTROLYTIC CONDUCTION:Conductance or conductivity is the property of the conductorwhich facilitates the flow of electricity through it. It is equal to the reciprocal of resistance,

i.e., Conductance (G) = 1/R

Unit: ohm1

or mho (1)

3.1 SPECIFIC CONDUCTANCE,sp:

Reciprocal of specific resistance is called Specific Conductance.

We Know that, R a

(where a : area of the electrode, : distance between the electrode)

R = a

where = specific resistance of substance.

+

a a

Now, sp.=1 1

R a=

or, sp =1

= G.

a

For electrolytic cells,a

is known as CELL CONSTANT.

Unit of sp: 1cm1or 1m1

3.2 EQUIVALENT CONDUCTANCE:It is the conductance of all ions produced by one gm equivalent ofan electrolyte. It is measured by

eq. sp V=

Where, eq.= Equivalent conductance

sp = Specific conductance in 1

cm1

V = Volume of solution of ml containing 1 gram equivalent of electrolyte

Unit of eq.: 1

cm2equiv

1

3.3 MOLAR CONDUCTANCE:It is the conductance of all the ions produced by ionization of one grammole of an electrolyte.

m sp V=

Unit of m: 1

cm2mole

1

3.4 Conductance of the electrolytes is known to depend upon: nature of electrolyte, i.e., strong or weak,

temperature and concentration of electrolyte in solution.

3.5 Variation of molar conductance with concentration by strong electrolyte is given by Huckel Onsagar

equation: mm

= Cb , where b is a constant depending on the nature of the solvent and

temperature and

m is molar conductance at infinite dilution. At infinite dilution the concentration, C

tends to be zero. At this large dilution m= mas C 0


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ELECTRO CHEMISTRY


3.6 KOHLRAUCHS LAW:At infinite dilution, when dissociation is complete, each ion makes a definitecontribution towards equivalent conductance of the electrolyte irrespective of the nature of the ion

with which it is associated and the value of equivalent conductance at infinite dilution for any

electrolyte is the sum of contributions of its constituent ions, i.e., = ++

3.7 DEGREE OF DISSOCIATION:At infinite dilution the ionization becomes 100%. At lower dilution theionization (dissociation into ions) is less than 100% and equivalent conductance become lower, i.e.,

eq


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ELECTRO CHEMISTRY


4.4 APPLICATION OF ELECTROCHEMICAL SERIES:

4.4.1 REACTIVITY OF METALS: The activity of the metal depends on its tendency to lose electrons. Thistendency depends on the magnitude of SRP (Standard Reduction Potential). The metal which has high

ve value (or smaller +ve value) of SRP, readily loses the electrons and converted into cations. Such a

metal is said to be chemically active. The chemical reactivity of metals decreases from top to bottom

in the series. For example:

(a) Alkali metals and alkaline earth metals having high ve values of SRP are chemically active.

These react with cold water and evolve H2 gas. These readily dissolve in acids forming

corresponding salts and combine with those substances which accept electrons.

(b) Metals like Fe, Pb, Sn, Ni, Co etc., which lie little down in series do not react with cold water

but react with steam to evolve hydrogen.

(c) Metals like Cu, Ag, An etc. which lie below hydrogen are less reactive and do not evolve

hydrogen from water.

4.4.2 ELECTROPOSITIVE CHARACTER OF METALS:The electropositive character also depends on thetendency to lose electrons. Like reactivity, the electropositive character of metal decreases from top to

bottom. On the basis of SRP values, metals are divided into three groups.(A) Strongly electropositive metals (having SRP near about 2.0V or more negative)

(B) Moderately electropositive metals (having SRP between 0.0 and 0.2V)

(C) Weakly electropositive metals (lie below hydrogen and having +ve SRP)

4.4.3 DISPLACEMENT REACTIONS:

(i) A metal higher in the series (lower SRP) displace the metal from its salt solution which is lower

in the series (higher SRP)

(ii) A non metal having high value of SRP will displace another non metal with lower SRP (i.e.

occupying position above in the series).

Ex: Fe + Cu2+

Fe2+

+ Cu

Cl2+ 2I 2Cl+ I2

5. ELECTROCHEMICAL OR GALVANIC CELLS:Electrochemical or Galvanic cell is a devicefor converting chemical energy into electrical energy. The electromotive force (EMF) of such cell is

directly proportional to the intensity of chemical reaction taking place in it. The chemical reaction

responsible for production of electricity normally takes place in two separate compartments. These

compartments are called half cells. Each half cell consist electrode and electrolytic solution. When the

two compartments are connected by a salt bridge and electrodes are joined by a wire through

galvanometer, the electricity begins to flow. One the example of Galvanic cell is Daniell Cell.

5.1 DANIELL CELL:

Salt bridgeCopper(II)

sulphate solution

(CuSO4)

Copper electrode

e

Zinc

electrode

Zinc sulphate

Solution

(ZnSO4)

e A

(i) When zinc and copper electrodes are joined by a wire the following observations are made:

(a) There is a flow of current through the external circuit.

(b) The Znrod loses its mass, while Curod gain in its mass.


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ELECTRO CHEMISTRY


(c) The concentration of ZnSO4solution increases, while the concentration of CuSO4solution

decreases.

(d) The solution in both the compartments remains electrically neutral.

(ii) The indirect redox reaction take place in the cell will be:

Anode or LHS compartment: Zn Zn2+

(aq) + 2e

Cathode or RHS compartment: Cu2+

(aq) + 2e Cu

Net cell reaction is: Zn + Cu2+

(aq) Zn2+

(aq) + Cu

The half cell in which oxidation occurs is called oxidation half celland the half cell in whichreduction occurs is called reduction half cell.

The electrode where oxidation takes place is called Anodeand where reduction occurs is termedCathode.

During the passage of electric current through external circuit, electrons flow from the anode tocathode and their polarity is negative and positive, respectively.

Chemical energy is converted into electrical energy.

The net cell reaction is the sum of two cell reactions.

5.2 SALT BRIDGE AND ITS SIGNIFICANCE: Salt bridge is usually an inverted U-tube filled withconcentrated solution of inert electrolyte (viz. KCl, KNO3, NH4NO3 etc.). Inert electrolyte is one

whose ions are neither involved in any electrochemical change nor do the react chemically with the

electrolytes in the two half cells. Gelatin or Agar-Agar (Plant Gel), is dissolved in a hot concentrated

aqueous solution of inert electrolyte and the solution thus formed is filled in the U-tube. The ends of

the U-tube are plugged with cotton wool as to minimize diffusion. The following are the functions of

the salt bridge:

(a) It connects the solutions of two half cells and completes the cell circuit.

(b) It prevents transference or diffusion of the solutions from one half cell to the other.

(c) It keeps the solutions in two half cells electrically neutral.

(d) It prevents liquid-liquid junction potential, i.e., the potential difference which arises between twosolutions when in contact with each other.

Salt bridge can be replaced by a porous partition which allows the migration of ions withoutallowing the solutions to intermix.

5.3 REPRESENTATION OF GALVANIC CELL:The two half cells required to form an electrochemicalcell can be represented by following rules:

(a) Reduction half cell is represented in right and oxidation half cell, in left.

(b) The separation of two phases (state of matter) is shown by a vertical line.

(c) The various materials present in the same phase are shown together with the help of commas.

(d) The two half cells are joined with the help of double vertical lines.

(e) The significant features of the substances viz. fugacity (pressure) of gas, activity(concentration) of ion etc. are indicated in brackets drawn immediately after writing the

substance.

For example: In Daniell cell, the cell reaction is Zn + Cu2+

Zn2++ Cu. The cell diagram is

Zn | Zn2+

| | Cu2+

| Cu

5.4 ELECTROMOTIVE FORCE OR EMF: The difference in potential which causes a current to flowfrom the electrode of higher potential to the one of lower potential is called EMF of the cell. It can be

represented as

Ecell= Higher reduction potential Lower reduction potential

Or0

cellE = SRP of Cathode SRP of Anode

Or0

cellE = SOP of Anode + SRP of Cathode

Or0

cellE = SOP of Anode SOP of Cathode


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ELECTRO CHEMISTRY


5.5 FREE ENERGY CHANGE IN GALVANIC CELLS:When a cell operates, work is done by the system,as electrical energy flows through external circuit. The quantity of electrical work done is measured in

terms of free energy change, G. This value is equal to the product of number of moles of electronsand emf of the cell.

G = nFEcell

If reactants and products are in the standard states, G= nFEcell

5.6 NERNST EQUATION: The electrode potential and EMF of the cell depend upon the nature of theelectrode, temperature and the activities (concentration) of the ions in solution. The dependence of

electrode and cell potential on activities of the ions in solution can be obtained from thermodynamic.

G = G+ RT ln Q

or, nFEcell = nF E cell + RT ln Q

or, cell cellRT

E E ln QnF

= Nernst equation

At 25C, ECell = E cell

0.059

logQ

n

(iii) Grefers to free energy change for the reaction when the various reactants and products arepresent at standard conditions. (298K is the temperature, 1M is the concentration and 1 atm. is

the pressure).

6. COMMERCIAL CELLS: Some of the electrochemical cells which are commonly employed as sourceof electrical energy can be classified as follows:

6.1 THE PRIMARY CELLS:Such cells can be used only so long the reactive materials are present. Oncethey exhausted, the cell can not be recharged by passing current through it.

Example:Leclanche or dry cell: represented as: Zn | NH4Cl (20%), ZnCl2| MnO2| Graphite

The reactions involved are:

Anode: Zn(s) Zn++ 2e

Cathode: 2MnO2(s) + H2O(l)+ 2e Mn2O3(s) + 2OH

The OH-

further causes the following secondary reactions:

NH4Cl + OH NH3+ Cl

+ H2O

Zn2+

+ 2NH3 + 2Cl Zn(NH3)2Cl2

The EMF of the cell is 1.5 Volts

6.2 THE SECONDARY CELLS:Such type of cells can be used again and again by recharging the cell.One of the examples is the Lead storage battery. In lead storage battery Pb acts as anode and lead

impregnated with lead oxide (PbO2) acts as cathode. The electrolyte is a nearly 37% H2SO4 solutionwith specific gravity of about 1.15 at 298K. The reactions are:

Anode: Pb(s) + SO2

4

(aq) PbSO4(s) + 2e

Cathode: PbO2(s) + 4H+(aq.) + 2e PbSO4(s) + 2H2O(l)

The EMF of the cell depends on the concentration of H2SO4viz. 1.9V at 7.4%, 2.0V at 21.4%

and 2.14V at 39.2% of H2SO4. To recharge the cell, it is connected with a source of potential

higher than that of the cell in such a way, that the cell now acts as the electrolytic cell, Pb is

deposited on the cathode, PbO2is formed at the anode and H2SO4is regenerated.

6.3 FUEL CELL:Fuel cells are electrochemical devices, which convert the energy of fuel by oxidationreaction into electrical energy. A fundamental example of fuel cell is the Hydrogen Oxygen cell.


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ELECTRO CHEMISTRY


H2 O2

O2H2

NaOH

Solution

Fuel cell

Ammeter

It consists of two electrodes made of porous graphite. Platinum is coated on the surface of the

electrodes. The electrodes are placed in aqueous solution of KOH or NaOH. H2and O2are bubbled

into the cell under 50 atm pressure. Electrods reactions are:

Anode: H2+ 2OH 2H2O + 2e

Cathode: O2+ H2O + 2e 2OH

Net reaction: 2H2(g) + O2(g) 2H2O. The EMF of the cell is 1.23 volts.


10/35

ELECTRO CHEMISTRY


ELECTRODE POTENTIAL

HASEEN SHURUAT (DPPI)

1. A metal having negative reduction potential when dipped in the solution of its own ions has a

tendency to

(A) remain neutral (B) become electrically positive

(C) go into the solution (D) be deposited from the solution

2. A metal rod is dipped in a solution of its ions. Its electrode potential is independent of

(A) temperature of the solution (B) concentration of the solution

(C) area of the metal exposed (D) nature of the metal

3. Indicator electrode is

(A) SHE (B) Calomel electrode

(C) Ag/AgCl electrode (D) Quinhydrone electrode

4. The following reactions represent the reduction of IO3 ion into I

ion in acidic and basic medium.

Predict in which medium IO3ion will act as a better oxidising egent?

IO3+ 6 H++ 6 e I+ 3H2O; E = + 0.907 V

IO3+ 3H2O + 6e I

+ 6 OH ; E = + 0.260 V

(A) Acid medium (B) Basic medium (C) Equally in both (D) none of these

5. The position of some metals in the electrochemical series in decreasing electropositive character is

given as: Mg > Al > Zn > Cu > Ag. What will happen if a copper spoon is used to stir a solution of

aluminium nitrate?

(A) the spoon will get coated with aluminium

(B) an alloy of copper and aluminium is formed

(C) the solution become blue

(D) there is no reaction

6. The metal that can not be obtained on reduction of its oxide by Al is

(A) K (B) Mn (C) Cr (D) Fe

7. The standard electrode potentials of four elements A, B, C and D are -3.05, -1.66, -0.40 and +0.80

volts. The highest chemical reactivity will be shown by

(A) A (B) B (C) C (D) D

8. The calomel electrode is reversible with respect to

(A) Hg22+

(B) H+ (C) Hg2+ (D) Cl

9. Which one of the following does not get oxidised by bromine water?

(A) Fe2+to Fe3+ (B) Cu+to Cu2+ (C) Mn2+to MnO4

(D) Sn2+to Sn4+

10. The standard electrode potential values of the elements A, B and C are 0.68, 2.50 and 0.50V

respectively. The order of their reducing power is

(A) A > B > C (B) A > C > B (C) C > B > A (D) B > C > A


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ELECTRO CHEMISTRY


PATHRILA RASTA (DPPII)

1. We have an oxidation reduction system: [Fe (CN)6]3+ e [Fe(CN)

6]4; E = + 0.36 V. At what

ratio of the concentration of oxidised and reduced from will the potential of the system be 0.28 V?

(A) 22.7 : 1 (B) 1 : 22.7 (C) 1 : 3.9 (D) 1 : 15

2. The standard reduction potential of oxygen in acidic solution is 1.23V (O2+ 4 H3O++ 4e 6H2O).

What is the standard reduction potential of oxygen in basic solution?

(A) +0.404 V (B) -0.404 V (C) +2.056 V (D) -2.056 V

3. The electrode potential of hydrogen electrode in neutral solution and 298K is

(A) - 0.41 V (B) zero (C) - 0.49 V (D) - 0.82 V

4. The standard reduction potential for the reaction [Co(H2O)

6]3++ e [Co(H

2O)

6]2+is about 1.8V. The

standard reduction potential for the reaction [Co(NH3)

6]3++ e [Co(NH

3)

6]2+is 0.1V. Which of the

complex ion, [Co(H2O)

6]2+or [Co(NH

3)

6]2+can be oxidised to the corresponding cobalt (III) complex,

by oxygen.2O / OH

E = 0.4V.

(A) [Co(H2O)

6]2+ (B) [Co(NH

3)

6]2+ (C) both (D) none of these

5. The standard potentials of OCl/Cl and Cl/Cl2 are 0.94V and 1.36V respectively. The E value of

OCl/Cl2will be

(A) 1.04 V (B) 0.42 V (C) 2.20 V (D) 0.52 V

6. Calculate the degree of hydrolysis and hydrolysis constant of aniline hydrochloride in M/32 solution

at 25C. Given:6 5 2 2

0

C H NH HCl|H (1atm )E = 0.188 V

7. Calculate the reduction potential at 25C for Fe3+/Fe2+electrode if the concentration of Fe2+ion is five

times that of Fe3+ion. 3 20

Fe |FeE + + = 0.77 volt.

8. Calculate electrode potential for the half cell Pt | H2(1 atm) | 0.357M-CH3COOH. Kafor CH3COOH

= 1.74 105.

9. Estimate the standard reduction potential of CuS/Cu electrode. Kspfor CuS = 8.5 1036and 2

0

Cu |CuE + =

+ 0.34 volt.

10. What is the standard electrode potential for the electrode, MnO4/MnO2in acid solution? 2

4

MnO |MnE + =

1.51V, 22MnO / Mn

E + = 1.23V.


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ELECTRO CHEMISTRY


GALVANIC CELL

HASEEN SHURUAT (DPPIII)

1. The e.m.f. of a galvanic cell composed of two hydrogen electrodes is 272 mV. What is the PH of the

solution in which the anode is immersed if the cathode is in contact with a solution of PH= 3?

(A) 3 (B) 6.7 (C) 7.6 (D) 1.6

2. For a cell reaction involving a two-electron change the standard emf of the cell is found to be 0.295V

at 25C. The equilibrium constant of the reaction at 25C will be

(A) 1 1010 (B) 1 1010 (C) 29.5 10 2 (D) 10

3. Tell which of the following statements accurately describes the effect of adding CN-to the cathode of

a cell with a cell reaction: Cd + 2Ag+2Ag + Cd2+, E = 1.2V

(A) E increases because Cd(CN)42

forms (B) E decreases because Cd(CN)42

forms

(C) E increases because Ag(CN)2

forms (D) E decreases because Ag(CN)2forms

4. The ECell

for Ag(s) | AgI (satd) || Ag+(0.10M) | Ag (s) is + 0.417 V. What is Ksp of AgI?

(A) 2.7 10-8

(B) 7.32 10-13

(C) 8.55 10-9

(D) 7.32 10-17

5. Assuming that hydrogen behaves as an ideal gas, what is the e.m.f. of the cell at 25C if P1= 640 mm

and P2= 425 mm: Pt | H

2(P

1) | HCl | H

2(P

2) | Pt?

(A) -0.005 V (B) -0.01 V (C) +0.005 V (D) +0.01 V

6. A depolariser used in dry cell batteries is

(A) NH4Cl (B) MnO2

(C) KOH (D) Na3

PO4

7. For a electrochemical cell Zn | Zn2+

(C1M) || Cu2+

(C2M) | Cu, the decrease in free energy at a given

temperature is a function of

(A) ln C1 (B) ln C2 (C) ln C2/C1 (D) ln C1/C2

8. At what PH does the potential (emf) for the disproportionation of chlorine change from a negative

value to a positive value, assuming 1.0 atm pressure and 1.0 M Concentration for all species except

hydrogen ion? Given:

Cl2+ 2e 2 Cl; E = 1.36 volt

OCl+ 2H++ e Cl2+ H

2O; E = 1.63 volt.

(A) 4.58 (B) 1.14 (C) 2.29 (D) 9.15

9. The emf of the cell at 298K Hg(l) | Hg2Cl

2(s), KCl sol. (1.0 N) | Quinohydrone | Pt, is 0.212V. What

is the PHof the quinohydrone solution, the potential of the normal calomel electrode is 0.2812V and

E for the quinohydrone electrode is 0.6996V, both at the same temperature.

(A) 3.5 (B) 7.0 (C) nearly zero (D) nearly 14

10. The potential of a cell consisting of an anode of silver in 0.10M-AgNO3solution and a cathode of Pt

immersed in a solution of 1.5M-Cr2O

72 , 0.75M-Cr3+ and 0.25M-H+ is (E0Ag+|Ag = 0.80V and

E0Cr2O

7

2|Cr

3+= 1.33 V)

(A) 0.41 V (B) 0.61 V (C) 0.51 V (D) 0.71 V


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ELECTRO CHEMISTRY


11. Two electrochemical cells are assembled in which the following reactions occur:

V2++ VO2++ 2H+2V3++ H2O; E

Cell= 0.616 V

V3++ Ag++ H2O VO2++ Ag (s) + 2H+; E

Cell= 0.439 V

If EAg

+|Ag

= 0.799 V, what is EV

3+|V

2+?

(A) -0.256 V (B) +0.256 V (C) +1.854 V (D) -1.854 V

12. The emf of the cell: H2(g) | Buffer || Normal calomel Electrode is 0.6885 V at 25 C, when barometric

pressure is 760 mm. What is the PHof the buffer solution? ECalomel

= 0.28 V.

(A) 3.46 (B) 6.92 (C) tending to zero (D) tending to 14

13. The emf of the cell obtained by combining Zn and Cu electrodes of a Daniel cell with normal calomel

elctrodes are 1.083V and 0.018V, respectively at 25 C. If the potential of normal calomel electrode

is 0.28V, find emf of Daniel cell.

(A) 1.065 V (B) 1.101 V (C) 0.803 V (D) 0.262 V

14. From the following E values for the half cells(i) D D2++ 2e; E = 1.5 V (ii) B++ e B; E = 0.5 V

(iii) A3A2+ e; E = 1.5 V (iv) C2++ e C+; E = + 0.5 V

Which combination of two half cells would result in a cell with largest potential?

(A) i and iii (B) i and iv (C) iii and iv (D) ii and iv

15. A Tl+/Tl couple was prepared by saturating 0.10M-KBr with TlBr and allowing Tl

+ ions form the

insoluble bromide to equilibrate. This couple was observed to have a potential 0.443V with respect

to Pb2+/Pb couple in which Pb

2+ was 0.10M. What is the Ksp of TlBr. Given 2

0

Pb |PbE + : = 0.126V

[Antilog(-4.44) = 3.6 105

, Antilog(-4.54) = 2.88 105

](A) 3.6 103 (B) 2.88 105 (C) 3.6 105 (D) None of these


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ELECTRO CHEMISTRY


PATHRILA RASTA (DPPIV)

1. Write the cell diagram for each of the following reactions and calculate E for each cell.

(a) AgBr (s) + 1/2 H2(g) Ag(s) + H++ Br

E0AgBr|Ag|Br

-= + 0.10 volt.

(b) PbSO4+ 2e Pb(s) + SO42; E = 0.359 volt

Pb2++ 2e Pb(s); E = 0.126 volt

(c) AgI (s) + e Ag(s) + I; E = 0.152 volt

Ag++ e Ag (s); E = + 0.80 volt

(d) Fe3+(0.1 M) + e Fe2+(1M); E = 0.77 volt

AgCl (s) + e Ag (s) + Cl(0.001 M); E = 0.22 volt

2. The standard reduction potential at 25C of the reaction 2H2O + 2e H2+ 2OH

is 0.8277 volt.

Calculate equilibrium constant for the reaction 2H2O H3O++ OHat 25C.

3. Calculate [Fe3+] at equilibrium when potassium iodide is added to a solution of Fe3+initially 0.50 M

until [I] = 1.0 M. Given 3 20

Fe |FeE + + = 0.770 V,

2

0

I |IE = 0.535 V.

4. If it is desired to construct the following voltaic cell to have ECell

= 0.086V, what [Cl] must be present

in the cathodic half cell to achieve the desired emf. Given K spof AgCl and AgI are 1.8 1010and

8.5 1017, respectively. Ag(s) | Ag+(sat. AgI) || Ag+(sat. AgCl, x M- Cl) | Ag (s)

5. The voltage of the cell given below is 0.46V.

Pt | H2| NaHSO3(0.4 M), Na2SO3(6.44 103M) || Zn2+(0.3 M) | Zn

If EZn2+|Zn= 0.763V, Calculate Ka2of H2SO4.

6. For the reaction, H2(g) + 2AgCl(s) + 2H2O() 2Ag(s) + 2H3O+(aq) + 2Cl(aq) at 25C, the standard

free energy of formation of AgCl(s), H2O() and (H3O++ Cl) (aq) are 109.7, 237.2 and 368.4

KJ/mol. Calculate what will be the cell voltage if this reaction is run at 25C and 1 atm in a cell in

which H2activity is unity and H3O+and Clactivities are each at 0.01M?

7. An alloy weighing 1.05g of Pb-Ag was dissolved in desired amount of HNO 3and volume was made

350 ml. An silver electrode was dipped in solution and Ecell

of the cell Pt, H2(1atm) | H+(1M) ||Ag+|Ag

was 0.503V at 298K. Calculate the percentange of lead in alloy. Given EAg+|Ag = 0.80V.

8. Estimate the cell potential of a Daniel cell having 1.0M-Zn2+and originally having 1.0M-Cu2+ after

sufficient ammonia has been added to the cathode compartment to make the NH3concentration 2.0M.

Given: EZn2+

|Zn= 0.76 V, ECu

2+|Cu

= + 0.34 V, Kffor Cu (NH3)42+

= 1 1012.

9. Calculate the minimum mass of NaOH required to be added in RHS to consume all the H+present in

RHS of the cell of emf + 0.701V at 25C, before its use. Also report the emf of cell after addition of

NaOH. Zn | Zn2+(0.1M) || HCl | H2(1 atm), Pt; EZn2+

|Zn= 0.76 V

10. The EMF of the cell: Ag, AgCl in 0.1MKCl || satd. NH4NO3 || 0.1MAgNO3, Ag is 0.45 volt at

25C. Calculate solubility product of AgCl. 0.1MKCl is 85% dissociated and 0.1MAgNO3is 82%

dissociated.


15/35

ELECTRO CHEMISTRY


11. Given E0= 0.08V for the Fe3+(cyt b) | Fe2+(cyt b) couple and E

0= 0.22V for the Fe3+(cyb c

1) | Fe2+

(cyt c1) couple, where E

0represents the standard state reduction potentials at PH= 7.0 at 25C and cyt

is an abbreviation for cytochromes. Determine E0and K for the equation

Fe3+(cyt c1) + Fe2+(cyt b) Fe2+(cyt c

1) + Fe3+(cyt b)

12. When metallic copper is shaken with a solution of a copper salt, the reaction Cu + Cu2+ 2Cu+proceeds. When equilibrium is established at 298K, [Cu2+]/[Cu+]2 = 1.66 106M1. If the standardpotential of the Cu2+| Cu half cell is + 0.337V, what is the standard potential of Cu+| Cu half cell?

13. When silver chloride is dissolved in a large excess of ammonia, practically all silver ion can be

assumed to exist in form of a single ionic species [Agx(NH3)y]x+

. Compute the values of x and y using

the two following cells:

(A) Ag | 0.4 x 10-3

M AgCl, 1M-NH3|| 40 x 10-3

M AgCl, 1M-NH3| Ag; Ecell= 0.1185V at 298K.

(B) Ag | 3 x 10-3

M AgCl, 1M-NH3|| 3 x 10-3

M AgCl, 0.1M-NH3| Ag; Ecell= 0.1263V at 298K.

14. For the reaction: H2(1atm) + 2AgCl(s) 2Ag(s) + 2H+(0.1M) + 2Cl(0.1M); G = 42927 J at

25C. Calculate the e.m.f. of the cell in which the given reaction takes place.

15. The emf of the cell: Cd(s) | CdCl2.5H2O (sat.) || AgCl(s) | Ag(s) for the reaction is

Cd(s) + 2AgCl(s) + aq CdCl2.5H2O (sat.) + 2Ag(s)

is +0.6915V at 0C and +0.6753V at 25C. Calculate the free energy change, enthalpy change and

entropy change at 25C.


16/35

ELECTRO CHEMISTRY


ELECTROLYSIS

HASEEN SHURUAT (DPPV)

1. Electrochemical equivalent is more for

(A) Hydrogen (B) Silver (C) Copper (D) Zinc

2. A current of 3.7 ampere is passed for 6 hours between Nickel electrodes in 0.50 litre of 2M solution of

Ni(NO3)2. The molarity of Ni2+at the end of electrolysis is

(A) 1.172 M (B) 0.172 M (C) 0.586 M (D) 2 M

3. The elctrochemical equivalent of two substances are E1and E

2The current that must pass to deposit

the same amount at the cathodes in the same time must be in the ratio of

(A) E1: E

2 (B) E

2: E

1 (C) E

1E

2: E

2 (D) E

1: E

2E

1

4. The same quantity of electricity is passed through one molar solution of H2SO

4and one molar solution

of HCl. The amount of hydrogen evolved from H2SO4as compared to that from HCl is

(A) the same (B) twice as such

(C) one half as such (D) dependent on concentration

5. Two electrolytic cells, one containing acidified ferrous chloride and another acidified ferric chloride

are connected in series. The ratio of iron deposited at cathodes in the two cells will be

(A) 3 : 1 (B) 2 : 3 (C) 1 : 1 (D) 3 : 2

6. A galvanic cell is set up from a zinc bar weighing 100g and 1.0L of 1.0M copper sulphate solution.

How long would the cell run if it is assumed to deliver a steady current of 1.0 ampere?

(A) 53.6 hr (B) 26.8 hr (C) 20.5 hr (D) 41.0 hr

7. Two platinum electrodes were immersed in a solution of CuSO4 and electric current was passed

through the solution. After some time, it was found that colour of CuSO4 disappeared with the

evolution of gas at the electrode. The colourless solution contains

(A) platinum sulphate (B) copper sulphate (C) copper hydroxide (D) sulphuric acid

8. The amount Faradays required to liberate 1 mole of an element indicates

(A) weight of element (B) conductance of electrolyte

(C) charge on the ion of that element (D) chemical equivalent

9. An ion is a reduced to the element when it absorbs 61020electrons. The number of equivalents of the

ion is

(A) 0.10 (B) 0.01 (C) 0.001 (D) 0.0001

10. A solution containing one mole per litre each of Cu(NO3)

2, Mg(NO

3)

2, AgNO

3, Hg(NO

3)

2 is being

electrolysed using inert electrodes. The values of standard electrode potential in volts are Ag+| Ag =

0.80V, Hg2+ | Hg = 0.79V, Cu2+ | Cu = 0.34V, Mg2+ | Mg = 2.37V. With increasing voltage the

sequence of deposit of metals on the cathode will be

(A) Ag, Hg, Cu, Mg (B) Mg, Cu, Hg, Ag (C) Ag, Mg, Cu (D) Cu, Hg, Ag

11. An ammeter and a copper voltameter are connected in series in an electric circuit through which aconstant direct current flows. The ammeter shows 0.525 ampere. If 0.635 gm of Cu is deposited in

one hour, what is the percentage error of ammeter?

(A) 2.09 % (B) 51 % (C) 2.05 % (D) 98 %


17/35

ELECTRO CHEMISTRY


12. In the lead storage battery the anode reaction is Pb(s) + HSO4 + H

2O PbSO

4(s) + H

3O++ 2e. How

many gm of Pb will be used upto deliver 1 amp for 100 hrs? (Pb = 208)

(A) 776 gm (B) 388 gm (C) 194 gm (D) 0.1 gm

13. Element A (at. wt. 112) and element B (at. wt. = 27) form chlorides. Solutions of these chlorides are

electrolysed seperately and it is found that when the same quantity of electricity is passed, 5.6 gm of

A was deposited while only 0.9gm of B was deposited. The valency of B is 3.The valency of A is

(A) 1 (B) 2 (C) 3 (D) 4

14. During the electrolysis of an aqueous salt solution, the PHin the space near one of the electrode was

increased and the other one was decreased. The salt solution was

(A) NaCl (very dilute) (B) ZnCl2 (C) NaCl (Conc.) (D) Cu(NO3)2

15. A hydrogen electrode placed in a buffer solution of CH3COONa and CH3COOH in the ratios x : y

and y : x has electrode potential values E1and E2volts, respectively at 250C. The PKa value of acetic

acid is

(A) (E1+ E

2)/ 0.118 (B) (E

2 E

1)/ 0.118 (C) -(E

1+ E

2)/ 0.118 (D) (E

1 E

2)/ 0.118

16. 100 ml of a buffer of 1M- NH3and 1M- NH4+are placed in two voltaic cells separately. A current of

1.5 amp is passed through both cells for 20 min. If electrolysis of water takes place only and the

electrode reactions are: Right: 2H2O + O2+ 4e 4 OH-and Left: 2H2O 4H

++ O2+ 4e, then the

PHof the

(A) right electrode will increase (B) left electrode will increase

(C) both electrode will increase (D) both electrode will decrease

17. The same current was passed successively through solution of zinc-ammonium sulphate and nickel-

ammonium sulphate rendered alkaline with ammonia. The weight of zinc and nickel deposited in a

certain time were found to be 22.89 gm and 20.55 gm, respectively. Given that the chemicalequivalent weight of zinc is 32.7, what is the chemical equivalent weight of nickel?

(A) 58.71 (B) 29.36 (C) 14.39 (D) 36.42

18. The preparation of LiOH by the electrolysis of a 35% solution of LiCl using a platinum anode led to a

current efficiency of 95%. What weight of LiOH was formed by the passage of 2.68A for 1 hr?

(A) 2.28 gm (B) 2.40 gm (C) 0.66 gm (D) 2.53 gm

19. Assuming that copper contains only iron, silver and gold as impurities. After passage of 140 ampere

for 482.5 seconds, the mass of anode decreased by 22.26 gm and the cathode increased by 22.011gm.

The percentage of iron and copper in the original sample are respectively

(A) 0.85%, 98.88% (B) 0.01%, 98.88% (C) 0.1%, 98.88% (D) 98.88%, 0.01%

20. After electrolysis of an aqueous sodium chloride solution, it was found that the solution is being

neutralised by 60 ml N HCl solution. During the same period of electrolysis, 3.18 gm of copper was

deposited in a copper voltameter in series. What is the percentage of the theoretical yield of sodium

hydroxide obtained?

(A) 40 % (B) 60 % (C) 30 % (D) 80 %


18/35

ELECTRO CHEMISTRY


PATHRILA RASTA (DPPVI)

1. 100 ml of 0.6N-CuSO4solution is electrolysed between two platinum electrodes till the concentration

in the residual liquid is 0.1N, when a steady current of 5.0 amp is used. How long should the current

be passed to get the above change?

2. An object whose surface area is 78.6 cm2 is to be plated with an even layer of gold 8.0 10 4 cmthick. The density of gold is 19.3 gm/ml. The object is placed in a solution of Au(NO3)3and a current

of 2.75 A is applied. Find the time required for the electroplating to be completed, assuming that the

layer of gold builds up evenly. (Au = 197)

3. The following galvanic cell

Zn | Zn (NO3)

2(aq) || Cu (NO

3)

2(aq) | Cu

(100 ml, 1M) (100 ml, 1M)

was operated as an electrolytic cell as Cu as the anode and Zn as the cathode. A current of 0.48

ampere was passed for 10 hours and then the cell was allowed to function as galvanic cell. What

would be the e.m.f. of the cell at 25C? Assume that the only electrode reactions occuring were thoseinvolving Cu | Cu2+and Zn | Zn2+. ECu

2+|Cu= + 0.34V, EZn

2+|Zn= 0.76V.

4. An alloy of lead (valency = 2)-thallium (valency = 1) containing 70% Pb and 30% Tl by weight canbe electroplated onto a cathode from a perchloric acid solution. How many hours would be required to

deposit 5.0 gm of this alloy at a current of 1.10 amp? (Pb = 208, Tl = 204)

5. Iridium was plated from a solution containing IrCl6yfor 2.0 hour with a current of 0.075 amp. The Ir

deposited on the cathode weighed 0.359 gm (a) what is the oxidation number of Ir in IrCl6y? (b) what

is the charge, y, on this ion? (Ir = 192)

6.

The electrolysis of cold sodium chloride solution produces sodium hypochlorite by reacting NaOHand Cl2throughly. How long will a cell operate to produce 1000 litre of 5.25% (by wt.) solution of

NaClO if the cell current is 2.50 103ampere? Assume that the density of solution is 1.0 gm/ml.

7. At the Nangal fertilizer plant in Punjab, hydrogen is produced by the elctrolysis of water. The

hydrogen is used for the production of ammonia and nitric acid (by the oxidation of ammonia). If the

average production of ammonium nitrate is 5000 Kg/day, estimate the daily consumption of

electricity per day.

8. 50 ml of 0.1M-CuSO4solution is electrolysed for 12 min. at a current of 0.06 amp. If Cu is producedat one electrode and oxygen at the other, what will be the P

Hof the final solution? For HSO4

-, Ka =

1.3102.

9. To reduce nitrobezene to aniline, 20 gm of C6H5NO2, 30 ml of an alcohol, 250 ml of water, 11 gm ofHCl and 1gm of SnCl2.2H2O were placed in the cathode space. After passing current at a rate of 26.5

amp-hour through the lead cathode electrolytic cell, 12.76 gm of aniline was produced. Determine the

current yield.

10. A test for complete removal of Cu2+ ions from a solution of Cu2+ is to add NH3(aq). A blue coloursignifies the formation of complex [Cu(NH3)4]

2+having Kf= 1.11013and thus confirms the presence

of Cu2+in solution. 250 ml of 0.1M-CuSO4is electrolysed by passing a current of 3.512 ampere for

1368 second. After passage of this charge, sufficient quantity of NH3is added to electrolysed solution

maintaining [NH3] = 0.10 M. If [Cu(NH3)4]2+is detectable upto its concentration as low as 1105M,

would a blue colour be shown by the electrolysed solution on addition of NH3.


19/35

ELECTRO CHEMISTRY


11. Perdisulphuric acid, H2S2O8can be prepared by electrolytic oxidation of H2SO4as 2 H2SO4H2S2O8+ 2H++ 2e. Oxygen and hydrogen are by products. In such an electrolysis, 0.72L of H 2and 2.35L of

O2were generated at STP. What is the weight of H2S2O8formed?

12. The electrode reactions for charging of a lead storage battery are:

PbSO4+ 2e Pb + SO42

PbSO4+ 2H2O PbO2+ SO42+ 4H++ 2e

The electrolyte in the battery is an aqueous solution of sulphuric acid. Before charging, the specific

gravity of the liquid was found to be 1.11 (15.7% H2SO4by wt.). After charging for 100 hours, the

specific gravity of the liquid was found to be 1.28 (36.9% H2SO4 by wt). If the battery contained

2 litres of the liquid, calculate the average current used for charging the battery.

13. By passing a certain amount of charge through NaCl solution, 9.2 litre of chlorine were liberated atSTP. When the same amount of charge is passed through a nitrate solution of metal M, 7.467 gm of

the metal was deposited. If the specific heat of metal is 0.216 Cal/C-gm, what is the formula of metal

nitrate? 14. Two litre solution of a buffer mixture containing 1.0M-NaH2PO4and1.0M-Na2HPO4is placed in two compartments (one litre in each) of an electrolytic cell. The platinum

electrodes are inserted in each compartment and 1.25 ampere current is passed for 212 min. Assuming

electrolysis of water only at each compartment, what will be PHin each compartment after passage of

above charge ? PKafor H2PO4= 2.15.

15. H2O2can be prepared by successive reactions:

2 NH4HSO4H2+ (NH4)2S2O8

(NH4)2S2O8+ 2H2O 2 NH4HSO4+ H2O2

The first reaction is an electrolytic reaction and second is steam distillation. What amount of current

would have to be used in first reaction to produce enough intermediate to yield 100 gm pure H 2O2per

hour. Assume current efficiency 50%.


20/35

ELECTRO CHEMISTRY


CONDUCTANCE

HASEEN SHURUAT (DPPVII)

1. Equivalence conductance at infinite dilution of NH4Cl, NaOH and NaCl are 129.8, 217.4 and 108.9

ohm-1, respectively. If the equivalent conductance of 0.01N solution of NH4OH is 9.33ohm-1cm2eq-1,

then the degree of dissociation of NH4OH at this temperature is

(A) 2.0 % (B) 0.039 % (C) 3.9 % (D) 4.7 %

2. Which of the following solution have highest resistance?

(A) 1N NaCl (B) 0.1N NaCl (C) 2N NaCl (D) 0.05 N - NaCl

3. Which pure substance will not conduct electricity?

(A) Molten NaCl (B) Molten KOH (C) Liquefied HCl (D) Liquid Hg

4. The resistance of a solution A is 50 ohms and that of solution B is 100 ohms, both solutions being

taken in the same conductivity cell. If equal volumes of solution A and B are mixed, what will be theresistance of the mixture using the same cell? Assume that there is no increase in the degree of

dissociation of A and B on mixing.

(A) 150 ohm (B) 75 ohm (C) 33.33 ohm (D) 66.67 ohm

5. In a conductivity cell, the two platinum electrodes, each of area 10cm2are fixed 1.5 cm apart. The cell

contained 0.05N solution of a salt. If the two electrodes are just half dipped into the solution which

has a resistance of 50 ohms, what is the equivalent conductance of the salt solution in ohm-1

cm2eq

-1.

(A) 120 (B) 60 (C) 240 (D) 6000

6. At 18C, the mobilities of NH4+and ClO

4ions are 6.6 104and 5.4 104cm2volt1sec1at infinite

dilution. What is the equivalent conductance of ammonium chromate solution in ohm-1cm2eq-1.

(A) 833.3 (B) 115.8 (C) 8.64 x 10-3

(D) 1.24 x 10-8

7. At 25C, the equivalent conductance at infinite dilution for HCl solution is 425 ohm-1cm2eqv-1, while

its specific conductance is 3.825 ohm-1 cm-1. If the apparent degree of dissociation is 90%, the

normality of the solution is

(A) 0.90 N (B) 1.0 N (C) 1.1 N (D) 1.2 N

8. The degree of dissociation of acetic acid in an aqueous solution of the acid is practically unaffected by

(A) adding a piece of sodium chloride

(B) adding a drop of concentrated hydrochloric acid

(C) diluting with water

(D) raising the temperature

9. The difference between a decinormal solution of HCl and a decinormal solution of acetic acid is that

(A) one of them conducts electricity and the other does not

(B) one of them is corrosive to the skin and the other is not

(C) one of them contains undissociated molecules of the acid and the other does not

(D) one of them decompose sodium carbonate and the other does not.

10. The resistance of 1N solution of acetic acid is 250 ohm, when measured in a cell of cell constant 1.15cm1. The equivalent conductivity in ohm1cm equivalent1of 1N acetic acid is

(A) 4.6 (B) 9.2 (C) 18.4 (D) 0.023


21/35

ELECTRO CHEMISTRY


PATHRILA RASTA (DPPVIII)

1. The specific conductance at 298K of AgCl solution in water was determined to be 1.826 x 10-6ohm-1

cm-1. The ionic conductances at infinite dilution, of Ag+and Cl are 61.92 and 76.34 ohm-1cm2eq-1

respectively. What is the solubility of AgCl in water?

(A) 9.2 x 108g/L (B) 1.32 x 105g/L (C) 1.9 x103g/L (D) 1.76 x 1010g/L

2. A cell whose resistance, when filled with 0.1M-KCl is 200 ohm, is measured to be 6400 ohm, when

filled with 0.003M-NaCl solution. All measurements were done at 298K. What is the equivalent

conductance of the NaCl solution, in ohm-1cm2eq-1? Equivalent conductance of 0.1M-KCl is

120 ohm-1cm2eq-1.

(A) 12.5 (B) 250 (C) 125 (D) 25

3. A big irregular shaped vessel contained water, the specific conductance of which was 2.56 105mho

cm1. 500 gm of NaCl was then added to the water and the specific conductance after the addition of

NaCl, was found to be 3.10 105mho cm1. Find the capacity of the vessel if it is fulfilled with

water. NaCl

= 149.9.

4. The equivalent conductance of 0.10N solution of MgCl2 is 97.1 mho cm2eq1at 25C. A cell withelectrodes that are 1.50 cm2 in surface area and 0.50 cm apart is filled with 0.10N-MgCl2 solution.

How much current will flow when the potential difference between the electrodes is 5 volts?

5. For H+and Na+, the values of symbol are 349.8 and 50.11. Calculate the mobilities of these ionsand their velocities if they are in a cell in which the electrodes are 5 cm apart and to which a potential

of 2 volt is applied.

6. The equivalent conductance of an infinitely dilute solution of NH4Cl is 150 and the ionic conductanceof OH and Cl ions are 198 and 76, respectively. What will be the equivalent conductance of the

solution of NH4OH at infinite dilution? If the equivalent conductance of a 0.01Nsolution of NH4OHis 9.6, what will be its degree of dissociation?

7. Calculate the ionic product of water at 25C from the following data: specific conductance of water =

5.8 108mho cm1. H+

= 350.0 and OH-= 198.0 mho cm2.

8. Calculate Ka of acetic acid if its 0.05N solution has equivalent conductance of 7.36 mho cm2eq1at25C.

3CH COOH= 390.7.

9. A dilute solution of KCl was placed between two platinum electrodes 10cm apart, across which apotential of 6 volts was applied. How far would the K+ ion move in 2 hours at 25C? Ionic

conductance of K+ion at infinite dilution at 25C is 73.52 mho cm2mol-1.

10. The specific conductance of a saturated solution of AgCl at 25C after substracting the specific

conductance of water is 2.28 106mho cm1. Find the solubility product of AgCl at 25C. AgCl

=

138.3 mho cm2.


22/35

ELECTRO CHEMISTRY


CHEMISTRY ARENA (LEVEL #I)

OBJECTIVE QUESTIONS HAVING ONLY ONE CORRECT OPTION

1. By how much would the oxidising power of MnO4 /Mn2+couple change if the H+ions concentration

is decreased 100 times?

(A) increases by 189 mV (B) decreases by 189 mV(C) will increase by 19 mV (D) will decrease by 19 mV

2. The standard reduction potential for the reaction Ag++ e Ag and Ag(NH3)2+

+ e Ag + 2NH3are+ 0.7991V and +0.373V, respectively. From these values and the Nearnst equation, what should be K

f

for the Ag(NH3)2+ion?

(A) 6.02 10-8

(B) 1.66 107 (C) 7.3 10

19 (D) 1.37 10

-20

3. The overall formation constant for the reaction of 6 mole of CNwith cobalt (II) is 1 1019. What is

the formation constant for the reaction of 6 moles of CNwith cobalt (III)? Given that

Co(CN)63-

+ e Co (CN)64-

; E = 0.83 VCo3++ e Co2+; E = + 1.82 V

(A) 8.23 1063

(B) 8.23 1025

(C) 1.22 10-26

(D) 1.22 10-64

4. Four colourless salt solutions are placed in separate test tubes and a strip of copper is placed in each.

Which solution finally turns blue?

(A) AgNO3 (B) Pb(NO3)2 (C) Zn(NO3)2 (D) Cd(NO3)2

5. A student made the following observations in the laboratory:

(I) Clean copper metal did not react with 1M-Pb(NO3)2solution

(II) Clean lead metal dissoles in 1M-AgNO3solution and crystals of Ag metal appeared(III) Clean silver metal did not react with 1M-Cu(NO3)2solution.

The order of decreasing reducing character of the three metals is

(A) Cu, Pb, Ag (B) Cu, Ag, Pb (C) Pb, Cu, Ag (D) Pb, Ag, Cu

6. Electrode potential will be more for hydrogen electrode with PH(at the same temperature)

(A) 4 (B) 3 (C) 2 (D) 5

7. If hydrochloric acid present in a hydrogen electrode coupled with a saturated calomel electrode is

titrated against ten times stronger solution of NaOH, the variance in electrode potential is

(A) electrode potential changes slowly first and more and more rapidly as the end point approaches

(B) electrode potential changes fast initially and very little change is observed as the end point

approaches

(C) electrode potential does not change at all during titration

(D) none of the above

8. The solution of CuSO4in which copper rod is immersed is diluted to 10 times, the reduction electrode

potential

(A) Increases by 0.030 V (B) Decreases by 0.030 V

(C) Increases by 0.059 V (D) Decreases by 0.059 V

9. K, Ca and Li metals may arranged in the decreasing order of their standard electrode potential as

(A) K, Ca, Li (B) Li, K, Ca (C) Li, Ca, K (D) Ca, K, Li


23/35

ELECTRO CHEMISTRY


10. A 0.1M solution of copper sulphate was electrolysed using copper electrodes, when the concentrations

of copper ions were found to be 0.12M and 0.06M respectively. The back emf developed at 27C is

(A) 20 mV (B) 5.2 mV (C) 8.8 mV (D) 10 mV

11. The cell reaction for the given cell is spontaneous if Pt, Cl2(P1atm) | Cl-| Cl2(P2atm), Pt

(A) P1> P2 (B) P1< P2 (C) P1= P2 (D) P1= 1 atm

12. What is the equilibrium constant of the reaction: 2Fe2++ Au+ 2 Fe++ Au3+. Given EAu+|Au

= 1.68 V,

EAu3+|Au

= 1.50 V, EFe3+|Fe2+

= 0.77 V.

(A) 5 1021

(B) 2 10-22

(C) 3 10-18

(D) 1.5 10-11

13. What is the emf of the cell Pt, (1atm) | CH3COOH (0.1M) || (0.01M) NH

4OH | H2(1atm), Pt. Kafor

CH3COOH = 1.8 105and Kbfor NH4OH = 1.8 10

5.

(A) 0.458 V (B) -0.458 V (C) -0.089 V (D) +0.89 V

14. The e.m.f. of a Daniel cell at 298K is E1, when the concentration of ZnSO4is 1.0M and that of CuSO4

is 0.01M, the e.m.f. changed to E2. What is the relationship between E1and E2?

(A) E1= E2 (B) E2= 0 (C) E1> E2 (D) E1< E2

15. When a lead storage battery is discharged

(A) SO2is evolved (B) lead sulphate is consumed

(C) lead is formed (D) sulphuric acid is consumed

16. For a reaction A(s) + 2B+ A2++ B(s); Kc has been found to be 1012. The EMF of the cell is

(A) 0.354 V (B) 0.708 V (C) 0.534 V (D) 0.453 V

17. Which of the following metals when coupled will give maximum e.m.f. for a voltaic cell?

(A) Fe and Cu (B) Pb and Au (C) Cu and Au (D) Ca and Cu

18. F2gas can not be obtained by the electrolysis of any aqueous fluoride salt because

(A) F2is the strongest oxidizing agent (B) F2eaisly combines with water

(C) F2readily combines with the electrodes (D) All of these

19. Copper can be deposited from acidified copper sulphate and alkaline cuprous cyanide. If the same

current is passed for a definite time

(A) the amount of copper deposited from acidic copper sulphate will be higher

(B) the amount of copper deposited from alkaline cuprous cyanide will be higher

(C) the same amount of copper will be deposited

(D) copper will not deposite in either case

20. The same current is passed through acidulated water and stannous chloride solution. What volume of

dry detonating gas at NTP is evolved from water, when 1.20 gm of tin is deposited from the other

solution? (Sn = 120)

(A) 448 ml (B) 336 ml (C) 224 ml (D) 672 ml

21. When molten ICI3is electrolysed using platinum electrodes

(A) I2is evolved at cathode and Cl2at anode

(B) Cl2is evolved at cathode and I2at anode

(C) I2is evolved at cathode and both I2and Cl2at anode

(D) electrolysis does not take place


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ELECTRO CHEMISTRY


22. When electric current is passed through a cell having an electrolyte, positive ions move towards the

cathode and negative ions towards the anode. If the cathode is pulled out of the solution, then the

(A) positive and negative ions will move towards the anode

(B) positive ions will start moving towards the anode, the negative ions will stop moving

(C) negative ions will continue to move towards the anode, the positive ions will start moving

randomly

(D) positive and negative ions will start moving randomly

23. When 10-6M-HCl is electrolysed

(A) O2is produced at the anode (B) H

2is produced at the anode

(C) Cl2is produced at the anode (D) Cl

2and O

2are produecd at the anode

24. A constant current flowed for 2 hours through a potassuim iodide solution, oxidising the iodide ion to

iodine. At the end of the experiment, the iodine was titrated with 25 ml of 0.08M Na 2S2O3solution.

What was the average rate of current flow in ampere?

(A) 0.268 amp (B) 2.68 amp (C) 0.536 amp (D) 0.134 amp

25. Anthracene, C14H10, can be oxidised anodically to anthraquinone, C14H8O2. What weight of

anthraquinone can be produced by the passage of a current of 1 amp of 60 minutes if the current

efficiency is 90 %?

(A) 6.98 gm (B) 1.16 gm (C) 41.90 gm (D) 0.99 gm

26. Most of the copper used to make wire has been electrically refined by depositing it from copper salts

solution (divalent) on to a cathode. What is the cost of electrical energy required per kg of copper if

the cost of electricity is Rs 4.00 per KWh and the cell operates at 0.33 volt? The electrochemical

equivalent of copper is 0.00033 gm/coul.

(A) Rs. 11.11 (B) Rs. 5.55 (C) Rs. 2.22 (D) Rs. 1.11

27. Electrolysis of an acetate solution produces ethane according to the reaction:

2CH3COOC2H6(g) + 2CO2(g) + 2e

What total volume of ethane and CO2would be produced at STP if a current of 0.5 amp is passed

through the solution for 482.5 min? Assume current efficiency 80%.

(A) 1.344 L (B) 2.016 L (C) 4.032 L (D) 1.792 L

28. To perform an analysis of a mixture of metal ions by electrodeposition, the second metal to be

deposited must not being plating out until the concentration ratio of the second to the first is about

106. What must be the minimum difference in standard potential of the two metals which form

dipositive ions in order for such an analysis to be feasible?

(A) 0.177 V (B) 0.354 V (C) 0.708 V (D) 0.005 V

29. Three faradays of electricity are passed through molten Al2O3, aqueous solutions of CuSO4 and

molten NaCl solutions. The amounts of Al, Cu and Na deposited at the cathodes will be in the ratio of

moles indicated

(A) 1 : 2 : 3 (B) 1.5 : 2 : 3 (C) 1 : 1.5 : 3 (D) 1 : 3 : 2

30. Electrolysis of a solution of HSO4 ions produces S2O8

2. Assuming 75% current efficiency, what

current should be employed to achieve a production rate of 1 mole of S2O82

per hour?

(A) 71.5 amp (B) 35.7 amp (C) 53.0 amp (D) 44.3 amp


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ELECTRO CHEMISTRY


MULTIPLE CHOICE QUESTIONS MAY HAVE ONE OR MORE THAN ONE CORRECT OPTION.

31. Which one of the following statement is/are incorrect regarding an electrochemical cell?

(A) the electrode on which oxidation takes place is called anode

(B) anode is the negative pole

(C) the direction of the current is same as that of the direction of flow of electrons

(D) the flow of current is partly due to flow of electrons and partly due to flow of ions

32. Which of the following statement(s) differentiate between electrochemical cell and electrolytic cell?

(A) spontaneous or non-spontaneous nature of the chemical process

(B) chemical reactions occuring at the electrodes

(C) positive and negative nature of anode

(D) dependence on Faradays law

33. Pick up the false statement(s):

(A) Galvanic cell reactions are always redox reactions

(B) In a galvanic cell made of cobalt and cadmium electrodes, cobalt electrode acts as anode

(C) Standard potential increases with increasing concentration of the electrolyte

(D) Calomel electrode is a reference electrode having 0.00 volt potential

34. Consider the cell: Ag (s), AgCl(s) | KCl (0.1M) | Hg2Cl2(s), Hg(l). The cell potential(A) Increases on increasing concentration of Clions.

(B) Decreases on decreasing concentration of Clions.

(C) is independent of concentration of Clions

(D) is independent of amounts of AgCl and Hg2Cl2COMPREHENSION BASED QUESTIONS HAVING ONLY ONE CORRECT OPTION

COMPREHENSION -I

The cell potential for the unbalanced chemical reaction:

Hg22++ NO3-

+ H3O+Hg2++ HNO2+ H2O

is measured under standard conditions in

the electrochemical cell shown in the accompanying diagram.

35. In which dish, the solution is acidic?

(A) Dish A (B) Dish B (C) Both (D) None

36. What is the equilibrium constant for the reaction?

(A) 1.97 (B) 4.76 (C) 2.18 (D) 1.40

37. How many moles of electrons pass through the circuit when 0.60 mole of Hg2+ and 0.30 mole of

HNO2 are produced in the cell that contains 0.50 mole of Hg2

2+ and 0.40 mole of NO3

- at the

beginning of the reaction?

(A) 0.30 (B) 0.60 (C) 0.15 (D) 1.20

38. How long will it take to produce 0.10 mole of HNO2 by this reaction if a current of 10 A passes

through the cell?

(A) 965 sec (B) 96500 sec (C) 1930 sec (D) 482.5 sec


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ELECTRO CHEMISTRY


COMPREHENSION -II

A fuel cell is the device to convert the energy of a fuel into electrical energy without the use of

heat engine, where the fuel is burnt directly. Such conversions are possible because the

combustion reactions are essentially redox reactions and highly exothermic as well as highly

exergonic. Electrical energy can be obtained indefinitely from a fuel cell as along as the outside

supply of fuel is maintained. In hydrogen oxygen fuel cell, the following reaction take place:

Anode reaction: 2H2 (g)+ 4OH(aq) 4H2O(l) + 4e

Cathode reaction: O2(g) + 2H2O(l) + 4e4OH(aq)

Overall reaction: 2H2(g) + O2(g) 2H2O(l)

The overall all reaction has a value of H= 285.8 kJ mol1and G= 237.39 kJ mol1 at

25C.

39. What is the standard EMF of the cell?

(A) 0.615 V (B) 1.23 V (C) 2.46 V (D) 0.74 V

40. Which of the following expressions gives Gfor the reaction in the fuel cell?

(A) 4 96500 1.23 J (B) 4 96500 1.23 J(C) 8.314 298 ln 1.23 J (D) 8.314 298 ln 286 J

41. How many litres of gaseous H2, when combined with excess O2in the fuel cell at 25C and 1.00 atm,are needed to produce 23.739 KJ of useful work under ideal conditions?

(A) 2.44L (B) 4.88L (C) 1.22L (D) 2.24L

42. Suppose the concentration of hydroxide ion in the cell is doubled. The cell voltage will be

(A) reduced by half (B) increased by a factor of 2

(C) increased by a factor of 4 (D) unchanged

43. What is the approximate value of Sfor the fuel cell reaction at 25C?

(A) 0.164 JK1

(B) 164 JK1

(C) 164 JK1

(D) 0.164 JK1

44. The theoretical efficiency of the fuel cell is given by

(A) 83.06 % (B) 100 %

(C) 67.53 % (D) 97.88 %

COMPREHENSION -III

Suppose that the S.H.E. was arbitrarily assigned a value of 1.00 volt for 2H++ 2e H2(g). What

would this do to the observed voltage under standard condition for each of the following:

(EZn2+|Zn= 0.76 volt, ECu2+

|Cu= + 0.34 volt)

45. Zn H2cell

(A) +0.34 V (B) -0.76 V (C) +1.76 V (D) -0.34 V

46. Cu H2Cell

(A) -0.34 V (B) +1.76 V (C) -1.76 V (D) +0.34 V

47. Zn Cu Cell

(A) +1.10 V (B) -1.10 V (C) 0.0 V (D) Indeterminate


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ELECTRO CHEMISTRY


COMPREHENSION -IV

A current of 15.0 A is employed to plate nickel in a NiSO4solution. Both Ni and H2are formed

at the cathode. The current efficiency with respect to formation of Ni is 60%. The density of

nickel = 8.9 gm/ml. (Ni = 58.7)

48. How much of nickel is plated on the cathode per hour?

(A) 16.43 gm (B) 32.85 gm (C) 19.7 gm (D) 9.85 gm

49. What is the thickness of the plating if the cathode consists of a sheet of metal 4.0 cm2which is to be

coated on both sides?

(A) 13.8 mm (B) 27.6 mm (C) 6.9 mm (D) 23.0 mm

50. What volume of H2at STP is formed per hour?

(A) 6.27 L (B) 3.76 L (C) 2.5 L (D) 5.01 L


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ELECTRO CHEMISTRY


AGNI PARICHHA (LEVEL #II)

1. Calculate electrode potential of Ag2S + 2e 2Ag + S2in a solution buffered at PH= 3 and which is

also saturated with 0.1M-H2S. For H2S, Ka1= 108and Ka2= 1.1 10

13, Ksp of Ag2S = 2 1049and

E0Ag

+|Ag= 0.80V.

2. Dissociation constant for Ag(NH3)2+

into Ag+

and NH3is 6 1014

. Calculate E for the half reaction:Ag(NH3)2

++ e Ag + 2NH3. Given Ag

++ e Ag has E = 0.799V.

3. The solubility product of CuCl is 2.29 107at 25C and 0Cl | CuCl | Cu

E is 0.129V. Calculate0

Cu |CuE + .

4. Determine potential of the cell Pt | Fe2+, Fe3+|| Cr2O72-

, Cr3+, H+| Pt in which [Fe2+] = 0.5M, [Fe3+] =

0.75M, [Cr2O72-

] = 2M, [Cr3+] = 4M and [H+] = 1M. Given:

Fe3++ e Fe2+; E = 0.77 V

14 H++ 6e + Cr2O72

2Cr3++ 7H2O; E = 1.35 V.

5. The temperature dependence of the standard state cell potential for the lead storage cell is E (volt) =

2.1191 + 1.62 104t + 8.5 107t2where t is in a degree celcius. Calculate G, S and H at25C.

6. Calculate the potential of the cell: Cu | Mn(s) | MnCl2(0.001M), HCl (0.01M) | O2(0.25 bar) | Pt | Cu.

Given, E = 1.185V for the Mn2+| Mn couple and 1.229V for the O2| H2O, H+couple.

7. Two students use same stock solution of ZnSO4and a solution of CuSO4. The emf of one cell is 0.03

V higher than the other. The concentration of CuSO4in the cell with higher emf value is 0.5M. Find

out the concentration of CuSO4in the other cell (2.303 RT/F = 0.06)

8. A cell contains two hydrogen electrodes. The negative electrode is in contact with a solution of 10

6

Mhydrogen ions. The emf of the cell is 0.118 volt at 25C. Calculate the concentration of hydrogen ions

at the positive electrode.

9. Two weak acid solutions HA1and HA2each with the same concentration and having pKavalues 3 and

5 are placed in contact with hydrogen electrode (1 atm, 25C) and are interconnected through a salt

bridge. Find emf of cell.

10. At 250C, HfH2O() = 56.74 kcal/mol and energy of ionisation of H2O() = 19.05 kcal/mol. What

will be the reversible emf at 25C of the cell Pt | H 2(g) (1atm) | H+|| OH | O2(g) (1atm) | Pt if at 26C

the emf increasing by 0.001158V.

11. Lactic acid, HC3H5O3, produced in 1 gm sample of muscle tissue was titrated using phenolphthaleinas indicator against OH

ions which were obtained by the electrolysis of water. As soon as OHions

are produced, they react with lactic acid and at complete neutralisation, immediately a pink colour is

noticed. If electrolysis was made for 115 sec using 15.6 mA current to reach the end point, what was

the percentage of lactic acid in muscle tissue.

12. In a ZnMnO2Cell, the anode is made up of Zn and cathode of carbon rod surrounded by a mixture

of MnO2, Carbon, NH4Cl and ZnCl2in aqueous base. The cathodic reaction is

2MnO2(s) + Zn2++ 2e Zn Mn2O4(s)

If 8 gm MnO2is present is cathodic compartment, how many day the dry cell will continue to give a

current of 4 103amp?


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ELECTRO CHEMISTRY


13. In an analytical determination of arsenic, a solution containing arsenious acid, H3AsO4, KI and a small

amount of starch is electrolysed. The electrolysis produces free I2from Iions and the I2immediately

oxidises the arseneous acid to hydrogen arsenate ion, HAsO42.

I2+ H3AsO3+ H2O 2I+ HAsO42+ 4H+

When the oxidation of arsenic is complete, the free iodine combines with the starch to give a deep

blue colour. If during a particular run, it takes 65.3 sec for a current of 10.5 mA to give an end point(indicated by the blue colour), how many gm of arsenic are present in the solution. (As = 75)

14. The electrolysis of a solution containing Cu(I), nickel and zinc as complex cyanides produced a

deposit weighing 0.175 gm. The deposit contained 72.8% by weight of Cu, 4.3% Ni and 22.9% Zn.

Assume that no other element was released and calculate the number of coulomb passed through the

solution.

15. A battery available for the electrode reaction involves the use of 25% of the Pb and PbO 2available init for reaction. What should be the minimum mass of lead in the free and combined states in a battery

designed to deliver 50 amp-hr? What is the standard free energy change for the reaction? Average

voltage of lead storage battery is 2.0V.


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ELECTRO CHEMISTRY


ENJOY THE VICTORY (LEVEL #III)

1. Zinc granules are added in excess to a 500 ml of 1.0M nickel nitrate solution at 25C until theequilibrium is reached. If the standard reduction potential of Zn

2+|Zn and Ni

2+|Ni are 0.75V and

0.24 V respectively, find out the concentration of Ni2+

in solution at equilibrium. [1991, 2 Marks]

2. A current of 1.70 ampere is passed through 300.0 ml of 0.160 M solution of a ZnSO4for 230 sec. witha current efficiency of 90%. Find out the molarity of Zn

2+ after the deposition of Zn. Assume the

volume of the solution to retain constant during the electrolysis. [1991, 4 Marks]

3. For the galvanic cell, Ag | AgCl(s), KCl(0.2M)|| KBr (0.001M), AgBr(s)| Ag, calculate the EMF

generated and assign correct polarity to each electrode for a spontaneous process after taking into

account the cell reaction at 25C. Ksp(AgCl) = 2.8 1010

; Ksp(AgBr) = 3.3 1013

[1992, 4 Marks]

4. An aqueous solution of NaCl on electrolysis gives H2(g), Cl2(g) and NaOH according to the reaction:

2Cl(aq) + 2H2O 2OH

(aq) + H2(g) + Cl2(g)

A direct current of 25 amperes with a current efficiency of 62% is passed through 20 litres of NaCl

solution (20% by weight). Write down the reactions taking place at the anode and the cathode. How

long will it take to produce 1 kg of Cl2? What will be the molarity of the solution with respect to

hydroxide ion? (Assume no loss due to evaporation) [1992, 3 Marks]

5. The dependence of electrode potential for the electrode Mn+/M with concentration under STP

conditions is given by the expression: E = E+n

0.0591log10[M

n+] (True/false) [1993, 1 Mark]

6. The standard reduction potential for half-cell: NO3(aq) + 2H

+(aq) + e NO2(g) + H2O(l) is 0.78V.

(i) Calculate the reduction potential in 8M-H+

(ii) What will be the reduction potential of the half-cell in a neutral solution? Assume all the otherspecies to be at unit concentration. [1993, 4 Marks]

7. Chromium metal can be plated out from an acidic solution containing CrO3according to the following

equation: CrO3(aq) + 6H+(aq) + 6e

Cr(s) + 3H2O. Calculate

(i) how many grams of chromium will be plated out by 24,000 coulombs and

(ii) how long will it take to plate out 1.5g of chromium by using 12.5A current? [1993, 2 Marks]

8. The standard reduction potential of the Ag+/Ag electrode at 298K is 0.799V. Given that for AgI,

Ksp= 8.7 1017

, evaluate the potential of the Ag+/ Ag electrode in a saturated solution of AgI. Also

calculate the standard reduction potential of the I/ AgI / Ag electrode. [1994, 3 Marks]

9. The Edison storage cells is represented as: Fe(s) | FeO(s) | KOH(aq) | Ni2O3(s) | Ni(s)[1994, 4 Marks]

The half-cell reactions are:

Ni2O3(s) + H2O(l) + 2e 2NiO(s) + 2OH

; E= + 0.40V

FeO(s) + H2O(l) + 2e Fe(s) + 2OH

; E= 0.87V

(i) What is the cell reaction?

(ii) What is the cell e.m.f.? How does it depend on the concentration of KOH?

(iii) What is the maximum amount of electrical energy that can be obtained from one mole of Ni2O3?

10. Although aluminium is above hydrogen in the electrochemical series, it is stable in air and water.

Explain. [1994, 1 Mark]


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ELECTRO CHEMISTRY


11. An excess of liquid mercury is added to an acidified solution of 1.0 103

M Fe3+

. It is found that 5%

of Fe3+

remains at equilibrium at 25C. Calculate Hg|Hg22E +

, assuming that the only reaction that

occurs is 2Hg + 2 Fe3+

Hg +22 + 2Fe

2+. (Given ++ 23 Fe|FeE

= 0.77 V) [1995, 4 Marks]

12. A dilute aqueous solution of Na2SO4 is electrolyzed using platinum electrodes. The products at the

anode and cathode are [1996, 1 Mark]

(A) O2, H2 (B) S2O 2

8 , Na (C) O2, Na (D) S2O 2

8 , H2

13. The standard reduction potential for Cu2+

| Cu is +0.34 V. Calculate the reduction potential at pH = 14

for the above couple. Kspof Cu(OH)2is 1.0 1019

. [1996, 3 Marks]

14. A standard hydrogen electrode has zero electrode potential because [1997(C), 1 Mark]

(A) hydrogen is easiest to oxidize

(B) this electrode potential is assumed to be zero

(C) hydrogen atom has only one electron

(D) hydrogen is the lightest element

15. Electrolysis of a solution of MnSO4 in aqueous sulphuric acid is a method for the preparation of

MnO2as per the reaction: Mn2+

(aq) + 2H2O MnO2(s) + 2H+(aq) + H2(g). Passing a current of 27

ampere for 2 hours gives only 1 kg of MnO2. What is the value of current efficiency? Write the

reactions taking place at the cathode and at the anode. [1997(C), 5 Marks]

16. The standard reduction potentials of Cu2+

|Cu and Cu2+

|Cu+are 0.337 V and 0.153 V respectively. The

standard electrode potential of Cu+|Cu half cell is [1997, 1 Mark]

(A) 0.184V (B) 0.827V (C) 0.521V (D) 0.490V

17. How many grams of silver could be plated out on a serving tray by electrolysis of a solution

containing silver in +1 oxidation state for a period of 8.0 hours at a current of 8.46 amperes? What isthe area of the tray if the thickness of the silver plating is 0.00254 cm? Density of silver is 10.5 g/cm

3.

[1997, 3 Marks]

18. Calculate the equilibrium constant for the reaction: Fe2+

+ Ce4+ Fe

3+ + Ce

3+. (Given ++ 34 /CeCeE

=

1.44V; ++ 23 /FeFeE

= 0.68V) [1997, 2 Marks]

19. The standard reduction potential values of three metallic cations, X, Y and Z are 0.52, 3.03 and

1.18 V respectively. The order of reducing power of the corresponding metals is [1998, 2 Marks]

(A) Y > Z > X (B) X > Y > Z (C) Z > Y > X (D) Z > X > Y

20. Calculate the equilibrium constant for the reaction, 2Fe3++ 3I 2Fe2++ I 3 . The standard reduction

potentials in acidic conditions are 0.77V and 0.54V respectively for Fe3+

| Fe2+

and I3 | I

couples.

[1998, 3 Marks]

21. Find the solubility product of a saturated solution of Ag2CrO4in water at 298K if the emf of the cell

Ag|Ag+(satd. Ag2CrO4 soln.)||Ag + (0.1M) | Ag is 0.164V at 298K. [1998, 6 Marks]

22. A gas X at 1 atm is bubbled through a solution containing a mixture of 1M Yand 1M Z

at 25C. If

the reduction potential of Z > Y > X, then, [1999, 2 Marks]

(A) Y will oxidize X and not Z (B) Y will oxidize Z and not X

(C) Y will oxidize both X and Z (D) Y will reduce both X and Z


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ELECTRO CHEMISTRY


23. A cell, Ag | Ag+|| Cu

2+| Cu, initially contains 1 M Ag

+and 1 M Cu

2+ions. Calculate the change in the

cell potential after the passage of 9.65 ampere of current of 1 hour. [1999, 6 Marks]

24. For the electrochemical cell, M | M+ || X

| X, E

0(M

+/M) = 0.44V and E

0(X/X

) = 0.33V. From this

data one can deduce that [2000(S), 3 Marks]

(A) M + X M++ Xis the spontaneous reaction

(B) M+

+ X

M + X is the spontaneous reaction(C) Ecell= 0.77V

(D) Ecell= 0.77V

25. Copper sulphate solution (250 mL) was electrolysed using a platinum anode and a copper cathode. A

constant current of 2 mA was passed for 16 minutes. It was found that after electrolysis the

absorbance of the solution was reduced to 50% of its original value. Calculate the concentration of

copper sulphate in the solution to begin with. [2000M, 3 Marks]

26. The following electrochemical cell has been set up: Pt(l) | Fe3+

, Fe2+

(a = 1) | Ce4+

, Ce3+

(a = 1) | Pt(II)

E(Fe3+/Fe2+) = 0.77V; E(Ce4+/Ce3+) = 1.61V. If an ammeter is connected between the two platinum

electrodes, predict the direction of flow of current. Will the current increase or decrease with time?[2000M, 2 Marks]

27. Saturated solution of KNO3is used to make salt-bridge because [2001(S), 3 Marks]

(A) velocity of K+is greater than that of NO

3

(B) velocity of NO

3 is greater than that of K+

(C) velocities of both K+and NO

3 are nearly the same

(D) KNO3is highly soluble in water

28. The correct order of equivalent conductance at infinite dilution of LiCl, NaCl and KCl is(A) LiCl > NaCl > KCl (B) KCl > NaCl > LiCl

(C) NaCl > KCl > LiCl (D) LiCl > KCl > NaCl [2001(S), 3 Marks]

29. The standard potential of the following cell is 0.23V at 15C and 0.21V at 35C.

Pt | H2(g) | HCl (aq) | AgCl(s) | Ag (s)

(i) Write the cell reaction

(ii) Calculate Hand Sfor the cell reaction by assuming that these quantities remain unchanged

in the range 15C to 35C.

(iii) Calculate the solubility of AgCl in water at 25C.The standard reduction potential of Ag

+/Ag couple is 0.80V, at 25C. [2001M, 10 Marks]

30. Standard electrode potential data are useful for understanding the suitability of an oxidant in a redox

titration. Some half cell reactions and their standard potentials are given below: [2002(S), 3 Marks]

MnO4 (aq.) + 8H

+(aq.) + 5e

Mn2+(aq.) + 4H2O(l) E= 1.51 V

Cr2O 27 (aq.) + 14H

+(aq.) + 6e

2Cr3+(aq.) + 7H2O(l) E= 1.38 V

Fe3+

(aq.) + eFe2+(aq.) E= 0.77 V

Cl2(g) + 2e2Cl(aq.) E= 1.40 V

Identify the only incorrect statement regarding the quantitative estimation of aqueous Fe(NO3)2.

(A) MnO4 can be used in aqueous HCl (B) Cr2O

27 can be used in aqueous HCl

(C) MnO4 can be used in aqueous H2SO4 (D) Cr2O

27 can be used in aqueous H2SO4


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ELECTRO CHEMISTRY


31. In the electrolytic cell, flow of electrons is from [2003(S), 3 Marks]

(A) Cathode to anode in solution (B) Cathode to anode through external supply

(C) Cathode to anode through internal supply (D) Anode to cathode through internal supply

32. Two students use same stock solution of ZnSO4and a solution of CuSO4. The emf of one cell is 0.03

V higher than the other. The conc. of CuSO4in the cell with higher emf value is 0.5 M. Find out the

conc. of CuSO4in the other cell (2.303 RT/F = 0.06) [2003M, 2 Marks]

33. The emf of the cell: Zn | Zn2+

(0.01M) || Fe2+

(0.001M) | Fe at 298K is 0.295V then the value of

equilibrium constant for the cell reaction is [2004(S), 3 Marks]

(A) 0295.032.0

e (B) 0295.032.0

10 (C) 0295.026.0

10 (D) 0591.032.0

10

34. Find the equilibrium constant for the reaction: In2+

+ Cu2+

In3+

+ Cu+at 298K. Given: ++/CuCu2E =

0.15V; ++/InIn0

2E = 0.40V, ++/InIn0

3E = 0.42V. [2004M, 4 Marks]

35. (a) For the reaction: Ag+(aq) + Cl

(aq) AgCl(s), Write the cell representation of above reaction

and calculate

cellE at 298K. Also find the solubility product of AgCl. Given:

Species G f (kJ/mol)

Ag+(aq) +77

Cl(aq) 129

AgCl (s) 109

(b) If 6.539102

g of metallic zinc is added to 100 ml saturated solution of AgCl. Find the value of2

10 2

[Zn ]log

[Ag ]

+

+.How many moles of Ag will be precipitated in the above reaction. Given that

Ag++ e

Ag; E= 0.80 V

Zn2+

+ 2e Zn; E= 0.76 V [2005M, 6 Marks]

36. We have taken a saturated solution of AgBr. Kspof AgBr is 12 10-14. If 10-7

moles of AgNO3are

added to 1 liter of this solution, find conductivity (specific conductance) of this solution in terms of

10-7

S.m-1

units. Given 0(Ag+) = 6 10-3Sm2mol-1, 0(Br) = 8 10-3Sm2mol-1, 0(NO3) = 7 10

-3

Sm2mol

-1. [2006, 6 Marks]

Tollens reagent is used for the detection of aldehyde when a solution of AgNO3 is added to

glucose with NH4OH then gluconic acid is formed.

Ag++ e Ag; E

0red= 0.8V

C6H12O6+ H2O C6H12O7(Gluconic acid) + 2H++ 2e; E

0oxd= -0.05V

Ag(NH3)2++ e Ag(s) + 2 NH3; E

0red= 0.337V

[Use 2.303 RT/F = 0.0592 and F/RT = 38.92 at 298K] [2006, 3 x 5 = 15 Marks]

37. 2Ag

+

+ C6H12O6+ H2O 2Ag(s) + C6H12O7+ 2H

+

. Find lnK of this reaction.(A) 66.13 (B) 58.83 (C) 28.30 (D) 46.29

38. When ammonia is added to the solution, pH is raised to 11. Which half cell reaction is affected by pH

and by how much?

(A) Eoxdwill increase by a factor of 0.65 from E0oxd

(B) Eoxdwill decrease by a factor of 0.65 from E0oxd

(C) Eredwill increase by a factor of 0.65 from E0

red

(D) Eredwill decrease by a factor of 0.65 from E0

red

39. Ammonia is always added in this reaction. Which of the following must be incorrect?

(A) NH3combines with Ag+to form a complex

(B) Ag(NH3)2+

is a stroger oxidising agent than Ag+

(C) In absence of ammonia, silver salt of gluconic acid is formed

(D) NH3has affected the standard reduction potential of glucose-gluconic acid electrode


34/35

ELECTRO CHEMISTRY


ANSWERS

ELECTRODE POTENTIAL

HASEEN SHURUAT (DPPI)

1. B 2. C 3. D 4. A 5. D 6. A 7. A8. A 9. C 10. D

PATHRILA RASTA (DPPII)1. B 2. A 3. A 4. B 5. B

6. 0.02, 1.356 x 10-5

7. 0.728V 8. 0.154V 9. 0.695V 10. 1.697V

GALVANIC CELL

HASEEN SHURUAT (DPPIII)

1. C 2. A 3. A 4. D 5. C 6. B 7.D

8. C 9. A 10. C 11. A 12. B 13. B 14.A

15. D

PATHRILA RASTA (DPPIV)

1. (a) (Pt)H2|H+||Br

-|AgBr|Br2; E

0= 0.10 V (b) Pb, PbSO4|SO

4-||Pb

2+|Pb; E

0= 0.233 V

(c) Ag, AgI|I-||Ag

+|Ag; E

0= 0.952 V (d) Ag,AgCl|Cl

-||Fe

3+|Fe

2+; E

0= 0.55 V

2. 1.0 x 10-14

3. 5.2 x 10-5

4. 6.8 x 10-4

5. 6.44 x 10-8

6. 0.458 V 7. 99.96% 8. 0.71 V

9. 1.264 gm, 0.3759 V 10. 1.7 x10-10

11. 0.14 V, 230 12. 0.521 V

13. x = 1, y =2 14. 0.34V

15.15.15.15. G = 130.332 KJ, H = 162.72 KJ, S = 562.8 J/K

ELECTROLYSIS

HASEEN SHURUAT (DPPV)

1. B 2. D 3. B 4. A 5. D 6. A 7. D

8. C 9. C 10. A 11. B 12. B 13. D 14. D

15. C 16. A 17. B 18. A 19. A 20. B

PATHRILA RASTA (DPPVI)1. 965 sec 2. 662 sec 3. 1.137 V 4. 1.00 hr

5. (a) +3 (b) -3 6. 15.1 hr 7. 4.188 x 105amp/day 8. 2.95

9. 85.1 % 10. Yes 11. 43.456 gm 12. 1.63 amp

13. M(NO3)3 14. Anode, 2.005; Cathode, 2.295 15. 315.35 amp

CONDUCTANCE

HASEEN SHURUAT (DPPVII)

1. C 2. C 3. C 4. D 5. A 6. A 7. B


35/35

ELECTRO CHEMISTRY


8. A 9. C 10. A

PATHRILA RASTA (DPPVIII)1. C 2. C 3. 2.37 x 10

5litre 4. 0.1456 amp

5. H+= 1.45 x 10

-3cm s

-1, Na

+= 2.08 x 10

-4cm s

-16. 0.0353 7. 1.0 x 10

-14

8. 1.76 x 10-5

9. 3.29 cm 10. 2.72 10-10

CHEMISTRY ARENA (LEVEL #I)

OBJECTIVE QUESTIONS HAVING ONLY ONE CORRECT OPTION1. B 2. B 3. A 4. A 5. C 6. C 7. A8. A 9. D 10.C 11.B 12.B 13.A 14.D15.D 16.A 17.D 18.A 19.B 20.B 21.A22.C 23.A 24.A 25.B 26.D 27.C 28.A29.C 30.A 31.C 32.AC 33.CD 34.CD 35.B36.B 37.B 38.C 39.B 40.B 41.A 42.D43.B 44.A 45.A 46.B 47.A 48.D 49.A50.C

AGNI PARICHHA (LEVEL #II)

1. - 0.127 V 2. 0.0189V 3. 30.52V 4. 0.56 V

5. -409.8 KJ, 39.5 J/K, -398.0 KJ 6. 2.452 V 7. 0.05M

8. 10-4

M 9. 0.059V 10. 1.165V 11. 0.1673%

12. 25.675 day 13. 2.66 x 10-4

gm 14. 229 coul 15. 1.544 Kg, -386 KJ

ENJOY THE VICTORY (LEVEL #III)

1.5.128 1018

mol L1

2. 0.154 M 3. 0.137 V 4. 48.69 hr., 1.408 M

5. False 6. (i) 0.833 V (ii) 0.367 V 7. (i) 2.1554 g (ii) 1336.15 sec

8. 0.325 V, 0.149 V 9. (ii) 1.27 V (iii) 2.45 105J 11. 0.792 V

12 .B 13.0.22 V 14.B 15. 94.8%

16.C 17. 272.18 g, 1.02 104cm

2 18.7.6 10

12

19. A 20. 6.26 107 21. 2.44 10

12

22. A 23. 0.010 V 24.B

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