Electrochemistry Questions and Answers

Na amalgam is prepared by electrolysis of NaCl solution using liquid Hg as cathode How long should the current of 10 amp be passed to produce 10 Na atomic mass of Na 23 Hg on a cathode of 10 g Ha

When 0 1 M Pb NO3 2 solution is titrated with 0 1 M KI solution then what will be the osmotic pressure in atm of solution when equivalence point is reached at 300 K Take R 0 08 atm L mol k

2 5 Faraday of electricity is passed through solution of CuSO The number of gram equivalents of copper deposited on the cathode would be a 1 4 b 2 e snad c 2 5 lousalsa d d 1 25

Calculate the equilibrium 4Br O 4H EO 0 16 V cell constant for the cell reaction 2Br 2H O

Exactly 0 2 mole electrons passed through two electrolytic cells in series containing CuSO4 a ZnSO4 respectively How many grams of each metal will be deposited on the respective cathod in the two cells

9 The e m f of a Daniell cell at 298 K is E Zn ZnSO CuSO Cu 4 0 01 M 1 0 M when the concentration of ZnSO4 is 1 0 M and that of Cusc is 0 01 M the e m f changed to E2 What is the relationsh between E and E2 1 a E E c E E b E E2 d E 0 E

0 05 M NaOH solution offered a resistance of 31 6 ohm in a conductivity cell at 298 K If t cell constant is 0 367 cm calculate its molar conductance

1 08 g of pure silver was converted into silver nitrate and its solution was taken in a beaker It was electrolysed using platinum cathode and silver anode 0 01 Faraday of electricity was passed using 0 15 volt above the decomposition potential of silver The silver content of the beaker after the above shall be a Og b 0 108 g

Electrolysis of aq CuSO4 causes 1 An increase in pH 2 A decrease in pH 3 Either decrease or increase 4 None

On passing electricity through dilute H SO4 solution the amount of substance librated at the cathode and anode are in the ratio 1 1 8 3 16 1 2 8 1 4 1 16

A silver wire dipped in 0 1 M HCl solution saturated with AgCl develops oxidation potential of 0 25 V If E 0 799 Ag Ag A 2 95 x 10 1 V the K of AgCl in pure water will be sp C 3 95 x 10 11 B 5 1 x 10 11 D 1 95 x 10 11 Lectrodes The pH of

1 Which of the following will increase the voltage of the cell with following cell reaction Sn 2Ag s Sn 2 2Ag s aq aq 1 Increase in the size of silver rod 2 Increase in the concentration of Sn 2 ions 3 Increase in the concentration of Ag ions 4 Decrease in the concentration of Ag ions

VILLUSTRATION 15 2 g of benzoic acid CH COOH dissolved in 25 g of benzene shows a depression in freezing point equal to 1 62 K Molal depression constant for benzene is 4 9 K kg mol 1 What is the percentage association of acid if it forms dimer in solution

No of total ions and resultant total charge in A B electrolyte 1 Five and 1 2 Five and 1 3 0 and 0 4 2 4 None of

The ratio of volume of gases obtain at anode when aq NaCl and aq Na SO4 is electrolysed connected in series is respectively 1 1 1 3 2 1 2 1 2 4 2 3

For the reduction of silver ions with copper metals the standard cell potential was found to be 0 46V at 25 C The value of standard Gibbs energy AG will be F 96500 C mol 1 98 0 kJ 3 89 0 J 2 89 0 kJ 4 44 5 kJ

The anode is the oxidising electrode by which electrons leave the electrolyte Loss of electrons from an atom or ion is called oxidation hence

Na Amalgam is prepared by electrolysis of aq NaCl solution using 10 gm Hg cathode How many Faraday s of electricity is required to prepare 18 7 Na Amalgam current Eff 50 x 10 A 0 081 F B 0 16 F C 0 2 F D 0 1 F 2 TAI 2 10 x 2 3 Sam2 mol 1 at infinite

for the cell at 298 K Ag s I AgCl s CH aq AgNO aq Ag s Which of following is correct A The cell emf will be zero when Ag in anodic compartment Ag in cathodic compartment B The amount of AgCl s precipitate in anodic compartment will decrease with the working of the cell C The concentration of Ag constant in anodic compartment during working of cell 0 059 1 Scanned with ACE AU log CamScanner 1 CI 1

Al OH sol 2 3 CdS sol 4 Gum 0 25 g lyophilic colloid is added to 100 ml gold solution to prevent the coagulation on adding 1 ml 10 NaC solution What will be gold number of lyophilic colloid 1 250 0525 3 25 2 125 4 0 25 d number of Gelatin Gum and Starch are 0 005 0 15 and 25 respectively Which colloid has highe 25 0035 0 25

Electrolysis of an acetate solution produces 57 ethane according to the Kolbe reaction 2CH COO C H 2CO 2e What volume of ethane is produced at 27 C and 720 mm Hg if a current of 0 4 ampere were passed through the solution for 8 hours and the electrode reaction is 75 efficient 1 2 7L 2 1 35 L 3 1 16 L 4 0 65 L

For a hypothetical reaction nx MY value of AH 133 kJ and AS 145 JK Calculate i the value of AG at 700 K ii value of AS surr and AS univ 16 43 JK the Ans i 14 5 kJ ii 161 43 JK

3 Which among the following has maximum potential for the half cell reaction 2H 2e H A 1 0 M HCI B 1 0 M NaOH C Pure water D A solution with pH 4

14 2 V 4 0 12 V 13 The equilibrium constant for the reaction 2MnO 6H 5H C O42Mn 8H O 10CC is approximately Given that E 2 MnO Mn 1 51 V A 00 0 0 49 V 1 10295 2 10339 3 10172 4 10490 On dilution specific conductance

The electrolysis of cold sodium chloride solution produces NaOH and Cl The Cl produced the disproportionately into NaOH solution to give sodium hypochlorite NaCIO and sodium chloride How long will a cell operate to produce 1 00 10 L of 7 45 w w solution of NaCIO if the cell current is 9 65 ampere Assume that the density of solution is 1 00 gm ml Fill your answer by multiplying it with 107 2

1 Consider the change in oxidation state of bromine corresponding to different emf values as shown in the given diagram dillups HBrO 3000 BrO 1 82 V BrO 3 4 ad obru ohas oe VEW BUL ai fiduridiliups 1 0652 V Br BrO3 1 5 V HBrO Br2 1 595 V go to tolls disproportionation Then the species undergoing is a BrO3 c Br2 UT 1 noi HBrO b BrO4 e 00 21 bon dieroverdi b BrO4

When Zn Cu 1 the electrical potential of Daniell cell is 1 1 V However a When E 1 1 V current flows from Zn to Cu ext b When Ext 1 1 V current flows from Cu to Zn c When E 1 1 V current flows from Zn to Cu ext d When F 1 V Walantrong flow from

C In a reversible reaction K K and AH 40 KCal The product will be obtained in less amount at 1 High pressure high temperature 2 Low pressure low temperature 3 High pressure low temperature 4 Low pressure high temperature

The ratio of number of moles of KMnO4 and K Cr O required to oxidise 0 1 mol Sn to Sn 4 in acidic medium 1 6 5 3 1 2 2 5 6 4 2 1

The resistance of 0 01 N solution of an electrolyte was found to be 200 ohm at 298 K using a conductivity cell of cell constant 1 5 cm The equivalent conductance of solution is A 750 mhocm eq B 75 mho cm eq C 750 mho cm eq D 75 mho cm eq of not

2 Given the standard electrode potentials K K 2 93V Ag Ag 0 80V Hg2 Hg 0 79V Mg2 Mg 2 37 V Cr Cr 0 74V Arrange these metals in their increasing order of reducing

A cell with two electrodes one of grey tin and the other of white tin both dipping in solution of NH SnCl showed zero e m f at 18 C What conclusion may be drawn from this 6 ROMOTIO a The e m f developed at the electrode solution phase boundary cancels the normal e m f els bisboate b Grey tin being non metallic ceases to provide a reversible electrode reaction c Electrode surface develops a protective layer and the cell develops a very large internal resistance C d The free energy change of the cell becomes zero

4 If the hydrogen electrodes in two solutions of pH 3 and pH 6 are connected by a salt bridge the emf of the result ing cell is A 0 177 V C 0 052 V B 0 3 V D 0 104 V

What will occur if a block of copper metal is dropped into a beaker containing a solution of IM ZnSO 1 The copper metal will dissolve and zinc metal will be deposited 2 No reaction will occur JEE MAINS ONLINE 2016 3 The copper metal will dissolve with evolution of oxygen gas 4 The copper metal will dissolve with evolution of hydrogen gas

The magnitude of standard reduction potentials of two metals X and Y are Y2 2e Y X2 2e X When two half cells of X and Y are connected to construct a galvanic cell electrons flow in the extern circuit from X to Y When X is connected to a standard SHE electrons flow in the external circuit fro X to SHE If a half cell X2 0 1M X is connected to another half cell Y2 1 0 M Y to construct galvanic cell at 25 C Calculate the EMF of cell 2 303 RT Given At 25 C F E 0 34V E 0 25V 0 06

12 The EMF of the cell M Mn 0 01M H 1M H g 1 atm Pt at 25 C is 0 82V Calculate th valency of the metal if the standard oxidation potential of the metal is 0 76V 2 303 RT F Take M 0 06 at 25 C

15 If potential of the cell is 0 98 V at 25 C Then calculate the pH in anodic compartment Pt s H 1 atm H aq Agt 0 1 M Ag s Given E Ag Ag 0 8 V and 2 303RT F 0 06

Write cell representation for following cells Cd aq Zn s Zn aq Cd s 6 2Ag aq H g 2H aq 2Ag s 2 c Cr 0 a 14H aq 6Fe2 aq 6Fe aq 2Cr aq 71 da ndard electrode potential

A zinc electrode is placed in a 0 1M solution at 25 C Assuming that the salt is 20 dissociated at this dilutions calculate the electrode reduction potential E Zn Zn 0 76V EQUILIBRIUM CONSTANT

EMF of the following cell is 0 634 volt at 298 K Pt H 1 atm H aq KCI IN Hg Cl s Hg Calculate pH of the anode compartment Given E CI Hg Cl Hg 0 28 and 2 303 RT F 0 059

Phenolphthalein does not act as an indicator for the titration between B NaOH and CH3COOH D Ba OH 2 and HCI A KOH and H SO4 C Oxalic acid and KMnO4

Which statement about standard reduction potentials is correct a E b E H H c A redox reaction is feasible if sum of SRP of oxidant and that of reductant is a positive quantity d K Cr O acid is stronger oxidising agent than KMnO acid 0 you D D 0 10

A variable opposite external potential Eext is applied to the cell Zn Zn 1 M Cu2 1 M Cu of potential 1 1 V When Eext 1 1 V and Eext 1 1 V respectively electrons flow from 1 anode to cathode and cathode to anode S 2 cathode to anode and anode to cathode 3 cathode to anode in both cases anode to cathode in both cases 4

Given E Cr 0 74 V E AMA 1 51 V MnO4 Mn2 E Cn0 Cr3 1 33 V E 1 36 V CI CI 3213 Based on the data given above strongest oxidising agent will be 1 CI 2 Cr 3 Mn2 4 M

40 Agcl can be obtained a by extraplotation of the graph A and C to zero concentration b by known values of A of AgNO3 HCl and HNO 3 c both a and b d None of these

E value for the cell reaction Cu l Cu 0 001 M Cu 0 1 1 In 0 01 3 RT F RT F In 0 01 2 4 RT F RT F M Cu is In 0 1 In 0 1

0 441V and E3 Fe 2 0 771V the standard EMF of the reaction Fe 2Fe 3 3Fe 2 will be 1 0 330 V 2 1 653 V 3 1 212 V 4 0 111 V If E Fe 2 Fe

9 An alloy of Pb Ag weighing 1 08 g was dissolved in dilute HNO and the volume made to 100 mL A silver electrode was dipped in the solution and the emf of the cell set up as Pt s H g H 1M Ag aq Ag s was 0 62 V If E is 0 80 V what is the percentage of Ag in the alloy At 25 C RT F 0 06 A 25 0 10 B 2 50 D 50

2 If equal quantities of electricity are passed through three voltameter containing FeSO4 Fe SO4 3 and Fe NO3 3 then which of the following is not true 1 Amount of iron deposited in FeSO4 and Fe SO4 3 is equal 2 Amount of iron deposited in Fe NO3 3 is 2 of the amount of iron deposited in FeSO4 3 Amount of iron deposited in Fe SO4 3 and Fe NO3 3 are equal 4 Same gas will evolve in all three cases at

5 Dal lake has water 8 2 x 10 2 L approximately A power reactor produces electricity at the rate 1 5 x 10 Cs at an appropriate voltage How many years would it take to elec trolyze the lake A 2 4 million years C 1 8 million years B 5 3 million years D 4 6 million years