Electrochemistry Questions and Answers

The standard reduction potentials at 25 C for the following half reactions are given against each Zn aq 2e Zn s 0 762 V Cr s 0 740 V Cr aq 3e 2H 2e Fe 2e H g 0 00 V Fe 0 77 V Which is the strongest reducing agent 1 Zn 3 H g 2 Cr 4 Fe aq

3 KNO EC0050 0 Which of the following displacement does not occur 1 Zn 2H Zn H 2 Fe 2Ag 3 Cu Fe2 Fe Ag Cu Fe 4 Zn Pb Zn Pb 4 AgNO3 IC W 1 3 47 T

CEC0032 28 Which of the following statements is correct 1 Oxidation occurs at anode in both galvanic and electrolytic cell 2 Reduction occurs at anode in both galvanic and electrolytic cell 3 Reduction occurs at anode in electrolytic cell where as oxidation occurs at cathode in galvanic cell 33 4 Oxidation occurs at anode in electrolytic cell where 34 as reduction occurs at anode in a galvanic cell

The most important secondary cell is the lead storage battery It consists of a lead anode and a grid of lead packed with lead dioxide as cathode A solution of sulphuric acid 38 percent by mass or having density 1 30 gm cm is used as an electrolyte ANODE TOD LEAD Pb CATHODE 0 LEAD DIOXIDE DIL Ha

EC0006 The specific conductances in ohm cm of four electrolytes P Q R and S are given in brackets Q 7 0x109 S 9 2 x 10 The one that offers highest resistance to the passage of electric current is 1 P 2 S 3 R P 5 0 x105 R 1 0 x10 0 4 Q EC0007 4 The n the c 11 The spes KCI is 0 conducta 1 140 3 1 4

4 Cannot be predicted 26 Given electrode potentials Fee 1 2e 21 E for the cell reaction 2Fe 212Fe 1 is 1 2 x0 771 0 536 1 006 V 2 0 771 0 5x0 536 0 503 V 3 0 771 0 536 0 235 V 4 0 536 0 771 0 235 V EC0030 Fe E 0 771 V E 0 536 V

rom Cu to Ag 3 electrons do not travel in the external circuit 4 in any direction EC0023 The direction of current in the Daniell cell when Zn and Cu electrodes are connected is 1 from Cu to Zn in the cell 2 from Cu to Zn out side the cell 3 from Zn to Cu outside the cell 4 in any direction in the cell

3 Build Up Your Understanding Which statement is not correct 1 Conductance of an electrolytic solution increases with dilution 2 Conductance of an electrolytic solution decreases with dilution 3 Specific conductance of an electrolytic solution decreases with dilution 4 Equivalent conductance of an electrolytic solution increases with dilution

electrolyte whatever be the nature of the a ion of the electrolyte Pre Medical Chemistry E for the half cell THE U

EC0016 dductance The HCI is sociation EC0019 19 In the galvanic cell Cu s Cu 1 M Ag 1 M Ag s the electrons will travel in the external circuit 1 from Ag to Cu 2 from Cu to Ag 3 electrons do not travel in the external circuit 4 in any direction EC0023

1 P 2 S 3 R 4 Q ECO0 The specific conductance of a salt of 0 01 concentration is 1 061 x 104 S cm Mc conductance of the same solution will be 1 1 061 x 10 S cm mol 2 1 061 S cm mol 3 10 61 S cm mol 4 106 1 S cm mol

0 Electrolysis of a solution of HSO ions Q 10 produces S O Assuming 75 current efficiency what current should be employed to achieve a production rate of 1 mol of S 0 per hour 1 71 50 A 3 142 96 A HS S 0 2 35 70 A 4 285 93 A S 0 1 75 gr far far farm Gal anty 1 71 50 A 3 142 96 A 2 35 70 A 4 285 93 A

Gallium is produced by the electrolysis of a solution made by dissolving gallium oxide in concentrated NaOH aq Calculate the amount of Ga s that can be deposited from a Ga III solution using a current of 0 510 A that flows for 30 0 min mass

Pre Medical Chemistry 125 8 The oxidation of SO by O to SO is exothermic reaction The concentration of SO will be minimum 1 Temperature is increased and pressure is kept constant 2 Temperature is reduced and pressure is increased 3 Both temperature and pressure are increased 4 Both temperature and pressure are decreased

ALLEN 65 M SO M is a monovalent metal ion has a K of 72 s 1 2 x 10 at 298 K The maximum concentration of M ion that could be attained in a saturated solution of this solid at 298 K is 1 3 46 x 10 M 3 2 8 x 10 M 2 2 89 x 10 M 4 7 0 x 10 M F C 73 F

Calculate AG at 298 K if the partial pressures of NO and N O4 are 0 37 atm and 1 64 atm respectively Express the free energy in kilojoules to two decimal places VAZO AG 6 10 O H

18 The solubility product of sparingly soluble Uni univalent salt AB type is defined as the product of ionic concentration in a 1 1 M solution 2 Concentration solution 3 Very dilute solution 4 Saturated solution IE0057

5 Effect of increasing temperature on equilibrium AH constant is given by log K log K 2 303R G statement is then for an endothermic reaction the false 3 AH positive positive 2 log K log K 4 K K C50028

The solubility of Co NH Cl CIO if the CO NH Cl 50 CIO 70 and the measured resistance was 33 50 in a cell with cell constant of 0 20 is 1 59 7 mmol L 3 39 7 m mol L 2 49 7 m mol L 4 29 7 m mol L

Standard reduction potentials of the half Q 18 reactions are given below 2e 2F aq Cl2 g 2e 2Cl aq 2e 2B E 2 85 V E 1 36V B210 12 s 2e 2 The strongest oxidising respectively are 1 Cl and Br 3 F and I E 1 06 V E 0 53 V and reducing agents 2 Cl and 1 4 Br and Cl 2e2F Cl 2e 2Cl aq 2 g 2e 28 aq Bran Iz s 2e 21 1 Cl e Br 3 F den I 3 E 2 85V E 1 36V E 1 06 V E 0 53V 42 3 2 Cl FT I 4 Br e CI

When 0 1 mol MnO2 is oxidised the quantity Q 3 of electricity required to completely oxidise MnO to MnO is 1 96500 C 3 9650 C 2 2 96500 C 4 96 50 C 0 1 MnO 1 96500 C 3 9650 C MnO i 3 MnO at a 2 2 96500 C 4 96 50 C

E0004 14 Ostwald s dilution law is not applicable for strong tively electrolytes because E0005 moles of 1 Strong electrolytes are completely ionised 2 Strong electrolytes are volatile 3 Strong electrolytes are unstable 4 Strong electrolytes often contain metal ions 150015 20

A planet is moving in an elliptical orbit If T U E and Lare its kinetic energy potential energy total energy and magnitude of angular momentum respectively then which of the following statement is true 1 T is conserved 2 U is always positive 3 E is always negative 1 4 L is conserved but the direction of vectos1081 will continuously change If ea up 1 3 ession 20

Experiment I Molten solution of LiH is electrolysed by using inert electrode If 1 F charge is given then x and y g of metal or gas is deposited liberated at respective electrode Experiment II Aqueous solution of NaNO3 is electrolysed by using inert electrodes If 1 F charge is given then p and z g of metal or gas is deposited liberated at respective electrode Find the value of x y p z if molar mass of Li H O Na and N are 7 g mol 2 g mol 32 g mol 23 g mol and 28 g mol respectively

0 Consider the following relations for emf of a electrochemical cell a emf of cell Oxidation potential of anode Reduction potential of cathode b emf of cell Oxidation potential of anode Reduction potential of cathode c emf of cell Reductional potential of anode Reduction potential of cathode d emf of cell Oxidation potential of anode Oxidation potential of cathode

18 At 25 C molar conductance of 0 1 molar aqueous solution of ammonium hydroxide is 9 54 ohm cm mol and at infinite dilution its molar conductance is 238 ohm cm mol The degree of ionisation of ammonium hydroxide at the same concentration and temperature is NEET 2013

None of the above If the distance between the centres of earth and moon is D and mass of earth is 81 times that of moon At what distance from the centre of earth gravitational field will be zero D N 4D 2 2D 3 GRO008 9D

Q 39 Using the data given below find out the strongest reducing agent Cr 0 Cr 1 33V Ecl cl EMNO Mn 1 15V E a Cl c Cr RE Cr Cr 1 1 36V 0 74V b Cr d Mn SHIGI FR 124951 Red poten Matza suta 34th1 Red ETOTI 55 11 Strongest RA 11 OX ETJTI 1

60 Electroche 12 The pressure of H required to make the potential electrode zero in pure water at 298 K is of H NEET 2016 1 10 atm 3 10 12 atm 2 10 14 atm 4 10 10 atm

cell Zn ZnSO4 0 01M CuSO4 1 0 M Cu the emf of this Daniel cell is E When the concentration of ZnSO4 is changed to 1 0 M and that of CuSO changed to 0 01 M the emf changes to E From the following which one is the relationship between E and E RT Given F 1 E E 3 F F 0 059 NEET 2017 Log Ker 2 E E 4 F 0 F Ken 0

In the electrochemical cell Zn ZnSO 0 01M CuSO 1 0 M Cu the emf of this Daniel cell is E When the concentration of ZnSO is changed to 1 0 M and that of CuSO changed to 0 01 M the emf changes to E From the following which one is the relationship between E and E RT Given F 1 E E 0 059 NEET 2017 2 E E 4 E 0 EK r

e Cu aq 24 The electrode potentials for Cu e aq are 0 15 V and 0 50 V and Cuaq e e Cu s respectively The value of EO 1 0 150 V 3 0 325 V will be Cu Cu AIPMT Prelims 2011 2 0 500 V 4 0 650 V

500 C is as follows 2 3 Al O3 3 1 4 5 V 3 2 5 V a 4 3 Al O 4 G 960 kJ mol 1 The potential difference needed for the electrolytic reduction of aluminium oxide Al2O3 at 500 C is at least AIPMT Mains 2012 2 3 0 V

Which will produce 1 gram equivalent of hydrogen 1 1 faraday charge passed through acidulated water 2 Na 23 gram with dil acid 3 12 gram Mg with steam 4 All of these will produce same amount of Ho

0 40 g of the following materials is sprayed into 100 cm3 0 200 M of hydrochloric acid Al Zn Ca Fe Which of the following statements is correct in connection with the volume of the gas evolved at same condition 1 5 Points The lowest volume is the product of Zn and the greatest one is the product of Al The lowest volume is the product of Zn and the greatest one is the product of Ca The lowest volume is the product of Fe and the greatest one is the product of Ca The lowest volume is the product of Fe and the greatest one is the product of Al

Consider the following standard reduction potentials Electrode a AgCl s eAg Cr b AgBr s e Ag Br c Agl s e Ag 1 d Ag S s 2e 2Ag S e AgNO3 aq eAg NO3 0 8 V On the basis of this information how many acids from the following can produce H g on reaction Ag s HCI HBr HI H S HNO3 Potential E 11 0 222 V 0 03 V 0 15 V 0 69 V

Li So is the anode correct A GLANCE 51 electrode potentials E 2 37V E 1 18 V E 0 15 V Which of the following reactions will proceed from left to right spontaneously 1 Mg2 V Mg V 2 Mg2 2Cu Mg 2Cu 3 V2 2Cu V 2Cu 2 4 V 2Cu V 2Cu 623 Consider the following Mg2 2e Mg V 2 2e V Cu2 e Cu using

Calculate the quantity of electricity i e charge delivered by a Daniel cell initially containing 1L each of 1 M Cu ion and 1M Zn which is operated until its potential drops to 1V Given EZn Zn 0 76V ECa Ca 0 34 V A 0 029 x 105C B 2 239 105 C C 1 92 x 105 C D 3 123 x 10 C

The temperature coefficient of a standard Cd cell is 5 0 x 10 5 Vk 1 whose emf at 25 C is 1 018 V During the cell operation the temperature will 1 increase 2 decreases 3 either 4 remains constant

SIF fX 0 s X s O g AH 90 kJ then heat 4 change during reaction of metal X with one mole of O2 to form oxide to maximum extent is 02 01 a 360 kJ c 180 kJ b 360 kJ d 180 kJ

43 If the enthalpy change for the reaction CH4 g Cl g CH3Cl g HCl g AH 25 kcal Bond energy of C H is 20 kcal mol greater than the bond energy of C Cl and bond energies of HH and H Cl are same in magnitude then for the reaction Fes 5 6 3 27 H2 g Cl2 8 HCl g AH 2 2 a 22 5 kcal mol c 32 5 kcal mol 0 x10 b 20 5 kcal mol d 12 5 kcal mol

and easiest way A 0 15 g sample of zinc ore was brought in solution as ZnCl and the zinc salt separated and treated with ferrocyanide solution as 2K4 Fe CN 6 3ZnCl K Zn3 Fe CN 6 2 6KCI 25 ml of 0 01 M ferrocyanide solution was required Determine percentage of zinc in the ore Zn 65 32 50

auring AgNO3 only H O is electrolysed and O2 is formed as 2H O 4H O 4e O2 formed at NTP due to passage of 2 A of current for 965 s is Question Type Single Correct Type 1 2 3 0 112 L 0 224 L 11 2 L

Which of the following is are correct statement statements for Lead storage battery A Cell is reversible B The total energy stored in the cell is limited by the moles of Pb s in the negative electrode or th mole of Pb in the positive electrode whichever amount is less C The emf of the cell depend upon the amount of Pb s in the cell D Upon completion of the charging process oxygen starts to form on the negative electrodes

The conductivities at infinite dilution of NH4CI NaOH and NaCl are 130 218 120 ohm cm eq 1 If equivalent conductance of N 100 solution of NH4 OH is 10 Then degree of dissociation of NH4OH at this dilution is 0 01 0 02 0 005

The minimum equivalent resistance obtained by combining three resistors of resistance 3 0 3 0 and 6 Q is Only one correct answer A 3 2 2 B 2 C 20 Review D 2

FL0014 When a tension F is applied in uniform wire of length and radius r the elongation produced is e When tension 2F is applied the elongation produced in another informare of length 20 and radius 27 made of same is 1 0 5e 2 1 0 e 3 1 5 e 4 2 0 e FL0015 22

55 Electrode potential for the following ha reactions are Mg Mg2 2e E 2 36 V Ag Ag e E 0 80 V The EMF for the cell reaction H 42 ade Mg s Agt ag Mg2 aq Ag s will be caried 1 1 56 V 3 3 16 V 2 4 f cathol 0 1 56 V 3 16 V

Applications of The important applications of electrochemical series are a Relative strength of oxidising and reducing agents In the series the elements are arranged in th increasing order of reduction potentials or decreasing order of oxidation potential Therefore the elemer at the top are good reducing agents while those at the bottom are good oxidising agents cell The om of the cell can be determined by knowing the standard electro

E 0 5V EBIB 0 2V Ect c 0 3V Ep 0 1V DID Based on above data select correct statements under standard condition A Best oxidizing agent is A B Best reducing agent is D C C can displace D from it s solution D Galvanic cell obtained by electrodes A and B shows the current flow from B to A in external circuit