Chemistry: Electrochemistry-1

Transcription

1 Chemistry: Electrchemistry-1 Slved Prblems Objective Prblem 1: Slutin: Prblem : Slutin: In the electrlysis f CuCl slutin using Cu electrdes, the weight f Cu ande increased by gram at cathde. In the ande. (a). mle f Cu + will g int slutin. (b) 56 ml O liberate (c) N lss in weight (d) gram f cpper ges int slutin as Cu + (d) During electrlysis f CuSO4 slutin using Cu electrdes, the cell reactin is Ande: Cu(s) Cu ++ + e Cathde: Cu ++ (aq) + e Cu(s) The lss in weight f ande is equal t gain in weight f cathde. During electrlysis f CuSO 4 using Pt-electrdes, the ph f slutin (a) increases (b) decreases (c) remains unchanged (d) cannt be predicted (b) In presence f inert electrde, the cell reactin is Ande HO 4H + + 4e + O Cathde: Cu ++ (aq) + e Cu(s)] Net cell reactin Cu ++ aq. + H O 4H + + Cu(s) + O Due t increase in [H + ], ph decreases. Prblem 3: A gas X at ne atm is bubbled thrugh a slutin cntaining a mixture f 1 MY and 1 M Z at 5 C. If the reductin ptential f Z Y X, then (a) Y will xidize X and nt Z (b) Y will xidize Z nt X (c) Y will xidize bth X and Z (d) Y will reduce bth X and Z Slutin: (a) The tendency t gain electrn is in the rder Z Y X Y + e Y X X + + e Prblem 4: The standard reductin electrde ptential values f elements A, B, C are +.68,.5, and.5 V respectively. The rder f their reducing pwer is (a) A B C (b) A C B (c) C B A (d) B C A Slutin: (d) Mre is the reductin ptential, mre is the pwer t get itself reduced r lesser is reducing pwer r greater is xidizing pwer.

2 Chemistry: Electrchemistry- Prblem 5: The value f equilibrium cnstant fr feasible cell reactin is (a) 1 (b) zer (c) = 1 (d) 1 Slutin: (d) E =.59 lgk, if E is +ve, thus K 1 n Prblem 6: Hw much will ptential f a hydrgen electrde change when its slutin initially at ph = is neutralized t ph = 7 (a) increase by.591 V (b) decrease by.591 V (c) increase by.413 V (d) decrease by.413 V Slutin: (d) H + + e 1 H(g), [E = E.591 lg Q] n =..591 P 1 H lg lg 1 [H ] 1 1 = lg1 =.413 V = 7 Prblem 7: Given that E =.44 V, and Fe / Fe E =.77V 3 Fe / Fe What is E =? 3 Fe / Fe (a).11v (b).11v (c).4 V (d).4 V Slutin: (c) ne ne (.44V) 1.77V E =.4V n Prblem 8: Fllwing are sme standard reductin ptential values fr the given half cell: i) A ++ + e A E = 1.7 V ii) B + + e B E =.7 V iii) C ++ + e C E =.54 V iv) D + + e D E = 1.5 V The cmbinatin f which tw half cells will give galvanic cell having maximum pssible emf. (a) (i) and (ii) (b) (I) and (iv) (c) (ii) and (iii) (d) (iii) and (iv)

3 Chemistry: Electrchemistry-3 Slutin: Prblem 9: (a) Since all the values are standard reductin ptential and s the tw half cells having maximum and minimum reductin ptential values will give a cell f maximum pssible emf. E E E cell RP(cathde) RP(ande) By hw much wuld the xidising pwer f the MnO 4 / Mn cuple change if the H + ins cncentratin is decreased 1 times? (a) increases by 189 mv (b) decreases by 189 mv (c) will increase by 19 mv (d) will decrease by 19 mv Slutin: (b) MnO 4 + 5e + 8H + Mn + + 4HO Accrding t Nernst equatin, E red = E red.59 [Mn ] lg 8 Let [H + ] initial = X 5 [MnO 4 ][H ].591 [Mn ] Ered(initial) = Ered lg 8 [H + X X ]final = 5 [MnO 4[X] [Mn ] 1 E red(final) = Ered lg 8 5 [MnO 4 ] [X].591 Ered(final) Ered(initial) = lg 1 16 =.1891 V 5 This E red decreases by.189 V. The tendency f the half cell t get reduced is its xidising pwer. Hence the xidising pwer decreases by.189v Prblem 1: A slutin f sdium sulphate in water is electrlysed using inert electrdes. The prducts at cathde and ande are respectively. (a) H,O (b) O,H (c) O,Na (d) O,SO Slutin: (a) Na + ins are nt reduced at cathde and SO 4 ins are nt xidized at ande Cathde: H (l) O (g) + 4H + (aq) + 4e Ande: H O(l) + e H (g) + OH (aq) Prblem 11: The standard xidatin ptentials f Cu/Cu + and Cu + /Cu + are.4v and.16v respectively. The standard electrde ptential f Cu + /Cu wuld be (a).18v (b).5v (c).8v (d).49v Slutin (b) Reactins Cu + + e Cu G = nfe Cu + Cu + + e G I = F.34 =.68F GII = F.16 =.16F

4 Chemistry: Electrchemistry-4 Adding, we get Cu + + e Cu E =.5V G III = G I + G II =.5F = FE Prblem 1: Acidified water is electrlysed using an inert electrde. The vlume f gases liberated at STP is.168l. The quantity f charge passed thrugh the acidified water wuld be (a) 96,5C (b) 9,65C (c) 965C (d) 168C Slutin: (c) H O H (g) + O (g) x x 3x =.168 x =.56L V H = x =.11L, V O = x =.56L 11.L f H at STP 1F.11L f H at STP.1F.56L f O at STP =.1F The amunt f electricity passed =.1F = 965C Prblem 13: The useful wrk dne during the reactin Ag (s) + 1 Cl(g) AgCl(s) Wuld be (a) 11kJ ml 1 (b) kj ml 1 (c) 55kJ ml 1 (d) 1 kj ml 1 Given -, PCl 1 atm and T = 98K Cl / Cl AgCl/Ag/Cl Frmatted: Fnt: Bkman Old Style, 11 pt, Bld Frmatted: Fnt: Bkman Old Style, 11 pt, Bld Frmatted: Fnt: Bkman Old Style, 11 pt, Bld Frmatted: Fnt: Bkman Old Style, 11 pt, Bld Slutin: (a) Fr the cell reactin Frmatted: Fnt: Bkman Old Style, 11 pt, Bld Ag(s) + 1 Cl(g) AgCl(s) E = 1.14V r E = E.59 1/ lg PCl 1 Under standard cnditins, PCl 1/ lg P Cl Useful wrk = Wmax = nfe = ( 1) ( 1.14) kj = 11 kj ml 1 Prblem 14: A current f.5 A is passed thrugh 4 ml f a. M slutin f NaCl fr 35 minutes. What will be the ph f the slutin after the current is turned ff? (a) 1.98 (b) 1.13 Frmatted: Fnt: Bkman Old Style, 11 pt, Bld Frmatted: Fnt: Bkman Old Style, 11 pt, Bld

5 (c) 1.48 (d) 9.4 Chemistry: Electrchemistry-5 Slutin (b) After electrlysis aqueus NaCl is cnverted int aqueus NaOH. The quantity f electricity passed = F 965 = F The number f equivalents f OH in frmed = Mlarity f NaOH = L poh = lg ( ) = 1.87 ph = 1.13 Prblem 15: Hw much charge shuld be supplied t a cell fr the electrlytic prductin f 45 gm NaClO 4 frm NaClO 3 if the ande efficiency fr the required reactin is 6%? (a) C (b) 6.67F (c) (d) 66.67F Frmatted: Fnt: Bkman Old Style, 11 pt, Bld Frmatted: Fnt: Bkman Old Style, 11 pt, Bld Slutin: (a) ClO4 + H + + e ClO3 + HO 45 Number f equivalents f NaClO4 = 4 4F 61.5 N. f Faradays = F = C 6 Prblem 16: The vlume f gases liberated at STP when a charge f F is passed thrugh aqueus slutin f sdium phsphate, is (a) 11.L (b) 44.8L (c) 33.6L (d).4l Slutin: (c) At ande HO O + 4H + + 4e At cathde H O + e OH + H After passage f F, ne mle f H and 1/ mle f O wuld be prduced. The ttal vlume is 33.6L. Prblem 17: Specific cnductance f.1 M KCl slutin is x hm 1 cm 1. When cnductivity cell is filled with.1 M KCl the cnductance bserved is y hm 1. When the same cell is filled with.1 M HSO4, the bserved cnductance was Z hm 1 cm 1. Hence specific cnductance f.1 M H SO 4 is: z (a) xz (b) xy (c) xz y (d) xy z Frmatted: Fnt: Bkman Old Style, 11 pt, Bld Frmatted: Fnt: Bkman Old Style, 11 pt, Bld Frmatted: Fnt: Bkman Old Style, 11 pt, Bld Frmatted: Fnt: Bkman Old Style, 11 pt, Bld

6 Chemistry: Electrchemistry-6 Specific cnductance x Slutin: (c) Cell cnstant = cm 1 Observed cnductance y Specific cnductance f.1 M HSO4 x = Observed cnductance Cell cnstant = z hm 1 cm 1 y Prblem 18: Amng the catin H +, Li +, Na + and K +, the ne with highest inic mbility and anther with lwest inic mbility respectively are: (a) [H +, K + ] (b) [K +, H + ] (c) [LI +, Na + ] (d) [H +, Li + ] Frmatted: Fnt: Bkman Old Style, 11 pt, Bld Frmatted: Fnt: Bkman Old Style, 11 pt, Bld Slutin: (d) H + in has the maximum inic mbility which is explainable by Grthus mechanics, Li + having the maximum charge density, is the mst hydrated in amng the lt and hence the lwest inic mbility. Prblem 19: The specific cnductance has the unit: (a) hm 1 cm 1 (b) hm.cm (c) hm cm 1 (d) hm 1.cm Slutin: (a) Specific cnductance = Observed cnductance a 1 cm = hm = hm 1 cm 1. cm Prblem : The specific cnductivity f slutin depends upn: (a) Number f ins as well as mbility f ins (b) Number f ins per c.c slutin (c) Number f ins per cc as well as mbilities f ins (d) Mbilities f ins nly Slutin: Subjective Prblem (c) Specific cnductance is the cnductance per c.c. slutin 1: HSO 3 SO 3 Ecell.76V E HSO HSO Zn / Zn 3 3 H SO3 E.76V cell Slutin: Ex.V Prblem : The E fr Ag + /Ag and Cr O 7 in acid medium t Cr +3 are.8 V and 1.33V. Find the value f E and G fr the cnversin f CrO7 t Cr +3 in acid when Ag gets xidised t Ag +. The cncentratins f dichrmate in, Cr(+3) and hydrgen in are. M,.5 M and.5 M, Ag + = 1 M Frmatted: Fnt: Bkman Old Style, 11 pt, Bld Slutin: 6Ag 6Ag + + 6e E =.8 V...(1) CrO7 + 14H + + 6e Cr + + 7HO E = 1.33 ()

7 Chemistry: Electrchemistry-7 Adding the bth we get, CrO7 + 6Ag + 14H + Cr Ag + + 7HO 3 6 E = E.33RT [Cr ][Ag ] lg n = nf [CrO 7 ][Ag] [H ] 6.59 (.5) (1) =.53 lg 14 6 (.5) = = =.457 V G = nfe = = 6463 J E =.53 V Prblem 3: Slutin: Calculate the slubility prduct and slubility f AgCl in the fllwing cell which has an emf f.455 vlts at 5 C. Ag/AgCl in.1 M KCl.1 M AgNO 3 Ag a1 =? a Ag Ag a 1 + e Ag a + e Ag Ag a Ag a1.591 a1 E = lg 1 a a.1 =.591 lg =.59 lg =.455 a1 a lg = 7.71 a anti lg 7.71 = a1.1 a1 = [Ag ] = [Cl ] = 1 1 Slubility prduct f AgCl = [Ag + ] [Cl ] = = Slubility f AgCl = [Ag + ] = [Cl ] = = mles/litre Prblem 4: Fr the galvanic cell Ag AgCl (s) KCl (.M) KBr (.1 M) AgBr (s) Ag Calculate the emf generated and assign crrect plarity t each electrde fr a spntaneus prcess after taking int accunt the cell reactin at 5 C [Ksp(AgCl) = ; Ksp (AgBr) = ]

8 Chemistry: Electrchemistry-8 Slutin: The given cell may be written as under Ag Ag + (C 1)Cl (.M) Ag + (C ), Br (.1 M) Ag The abve cell in a cncentratin cell with the cell reactin [Ag + ]RHS [Ag + ]LHS [Ag ] LHS and cell ptential =.59 lg [Ag ] RHS [KspAgCl]/[Cl ] Ecell =.591 lg [KspAgBr]/[Br ] =.591 lg =.591lg =.591 lg 4.4 = =.379 vlts Since cell ptential is negative, the cell reactin will be spntaneus in the reverse directin i.e. AgCl + Br AgBr + Cl with Cl AgCl Ag serving as cathde (+ve terminal) and Br AgBr Ag as ande ( ve terminal). The spntaneity is due t the fact that AgBr is less sluble than AgCl. Prblem 5: Slutin: Prblem 6: The standard reductin ptential fr the half cell. NO 3 (aq) + H + (aq) + e NO (g) + H O (l) is.78 V a) Calculate the reductin ptential in 8M H + b) What will be the reductin ptential f the half-cell in a neutral slutin? Assume all ther species t be at unit cncentratin Fr the half cell reactin NO3 (aq) + H + (aq) + e NO(g) + HO(l) The Nernst equatin is E = E.59 [Pr ducts] lg n [Reactants].59 1 =.78 lg = lg 8 (8) =.833V Substituting this value fr case (b).59 1 E =.78 lg 7 (1 ) = =.367V Calculate EMF f the cell Pt, H (.1 atm) slutin (ph = 4) M KCl slutin (saturated with AgCl) Ag 1 and equilibrium cnstant f the cell reactin at 5 C. Given E =.8 V and Ag,Ag Ksp (AgCl) = at 5 C.

9 Chemistry: Electrchemistry-9 1 Slutin: Cell reactin: H + Ag + H + + Ag(s) 4 [H ] 1 Q = = = / 1/ 9 [H ] [Ag ] (.1) (4.361 ) ( ph = 4 [H + ] = 1 4 M. [H ] = P H =.1 atm, and 11 K Ksp = [Ag + ] [Cl ], [Ag + ] = sp [Cl ] = = M) 1 Ecell = E Cell.59 Q = E E 1 Ag,Ag H, H.59 lg Q = (.8 ).59 lg ( ) =.8.59 (lg ) =.8.59 ( ) =.514 Alternate methd: E = E +.59 lg [Ag + ] Ag,Ag Ag,Ag = lg ( ) = ( ) = =.367 1/ PH E 1 H = E, H 1.59 lg H H [H ] 1/ 1 =.59 lg 4 1 = =.65 Ecell = E E Ag,Ag 1 H, H = =.513 V E = E.59 lg Q At equilibrium: E = and Q = K = equilibrium cnstant S, E =.59 lg K.8 =.59 lg K K = Prblem 7: Slutin: Cnstruct the cell crrespnding t the reactin: 3Cr + (1M) Cr 3+ (1M) + Cr(s) and predict if the reactin is spntaneus. Als calculate the fllwing i) H and S f the reactin at 5 C. ii) G f the reactin at 5 C when Cr + =.5 M and Cr 3+ =.5 M Given E =.5 V, E 3 =.41 V Cr 3,Cr G f the reactin at 35 C = 7.5 kj Cr,Cr The cell crrespnding t the given reactin is as fllws.

10 Chemistry: Electrchemistry-1 Pt Cr + (1M), Cr 3+ (1M) Cr + (1M) Cr(s) I Cr e Cr(s), GI 3FE 3 Cr,Cr II Cr 3+ + e Cr + O, GII FE 3 Cr,Cr Eq. I Eq. II: Cr + + e Cr(s), G = 3.5 F.41 F = 1.91 F G = FE = 1.91 F Cr,Cr E = 1.91 Cr,Cr =.955 V ECell E Cr E = = V 3,Cr Cr,Cr E cell is +ve s G is Ve and hence the given reactin is spntaneus i) G = nfe cell = J = kj Frm Gibb's Helmhltz equatin ( G) G = H + T T P ( ) = H = H H = kj HG S = = T 98 =.76 kj K 1 = 76 kj K 1 3 [Cr ] (.5) ii) G = G + RT ln Q, Q = = [Cr ] (.5) = lg.5 = = = kj Prblem 8: Cnsider the cell: Pb PbSO4 NaSO41HO The temperature cefficient f the emf f abve cell is.174v deg 1 and heat f reactin is kj. Calculate emf f the cell. Slutin: The cell reactin is At ande Pb(s) + SO4 PbSO4(s) + e At cathde HgSO4(s) + e Hg(l) + SO4

11 Chemistry: Electrchemistry-11 Pb(s) + HgSO4(s) PbSO4(s) + Hg(l) i.e. the number f electrns invlved are tw, substituting the values f knwn terms in equatin (3) J = () (965 J V 1 ) E + (98 K ) (965 J V 1 ) () (.174 VK 1 ) E =.9645V Prblem 9:ESlutin: Prblem 1:SlutinPrblem 11:+ Slutin:Prblem 1:Slutin:Prblem 13:) E.8V Slutin: E.8V E.8V K sp Ag / Ag Ag / Ag Ag / Ag 8 K sp M [Ag ] C [Cl ] x [Ag ] A.9x 1.86 Ecell Ecell lg lg lg 51.x Prblem 1 1 [Ag ] C [Ag ] L.H.S. x 14: E.8VSlutin: E Ag / Ag x.8v Ered.8V Ecell.V K [Ag ] R.H.S x x Ecell Ecell lgk.788 lg lg n x ; x=.311 [Ag ] L.H.S..311 M Prblem.5 de de :Slutin: nf T 4 E dt 5.51 dt 38 98

12 Chemistry: Electrchemistry-1 Assignments (New Pattern) SECTION I Single Chice Questins 1. 3 The density f Cu is 8.94 g cm. The quantity f electricity needed t plate an area 1 cm 1 cm t a thickness f 1 cm using CuSO 4 slutin is (a) C (b) 7 17 C (c) C (d) 348 C.. In an electrlysis f an aqueus slutin f sulphate,.4 L f xygen at STP was liberated at ande. The vlume f hydrgen at STP liberated at cathde wuld be (a) 1. L (b).4 L (c).6 L (d) 4.8 L. 3. In the electrlysis f CuCl slutin using cpper electrde, if.5 g f Cu is depsited at cathde, then at ande (a) 89 ml f Cl at STP is liberated (b) 445 ml f O at STP is liberated (c).5 g f cpper is depsited (d) a decrease f.5 g f mass take place 4. The reactin ccurring at ande when the electrlysis f CuSO 4 is dne using Pt electrde, is (a) Cu Cu e (b) SO4 H O H SO4 O 4e (c) H O O 4H 4e (d) Cu Cu e 5. Which f the fllwing is crrect? (a) Cathde is psitive terminal in an electrlytic cell (b) Cathde is negative terminal in a galvanic cell (c) Reductin ccurs at cathde in either f cells (d) Oxidatin ccurs at cathde in either f cells. 6. Which f the fllwing statements is crrect? (a) Oxidatin ccurs at ande in bth galvanic and electrlytic cells (b) Reductin ccurs at ande in bth galvanic and electrlytic cells (c) Reductin ccurs at ande in electrlytic cell whereas xidatin ccurs at cathde in a galvanic cell

13 Chemistry: Electrchemistry-13 (d) Oxidatin ccurs at ande in electrlytic cell whereas reductin ccurs a ande in a galvanic cell. 7. By hw much will the ptential f half-cell Cu Cu Change if the slutin is diluted t 1 times at 98 K? (a) Increases by 59 mv (b) Decreases by 59 mv (c) Increases by 9.5 mv (d) Decreases by 9.5 mv Given that E values f Ag Ag,K K,Mg Mg and Cr Cr are.8 V,.93 V,.37 V, and.74 V, respectively. Which f the fllwing rder regarding the reducing pwer f metals is crrect? (a) Ag > Cr > Mg > K (b) Ag < Cr < Mg < K (c) Ag > Cr > K > Mg (d) Cr > Ag > Mg > K. 9. A current f 9.65 A is drawn frm a Daniel cell fr exactly 1 h. If mlar masses f Cu and 1 1 Zn are 63.5 g ml and 65.4 g ml, respectively, the lss in mass at ande and gain in mass at cathde, respectively are (a) g, g (b) g, g (c).86 g, 3.54 g (d) 3.54 g,.86 g 1. In acidic medium MnO 4 is an xidizing agent. MnO4 8H 5e Mn If H in cncentratin is dubled, electrde ptential f the half cell MnO 4, Mn will: (a) increase by 8.46 mv (b) decrease by 8.46 mv (c) increase by 14.3 mv (d) decrease by 14.3 mv. 11. The inic mbilities f Li +, Na +, K +, Rb + and Cs + increase in the rder: (a) Li +, Na +, K +, Rb + and Cs + (b) Cs +, Rb +, K +, Na + and Li + (c) Na +, Li +, Rb +, Cs + and K + (D) Nne f these 1. The specific cnductance f 1.M slutin a weak mnbasic acid is.5 hm 1 cm 1 while inic cnductances f its catin and anin are 1 and 13 hm 1 cm ml 1 respectively. The dissciatin cnstant f the acid is apprximately. (a) 1 3 (b). (c) (d) Nne f these 13. Fr which f the fllwing electrlytes, mlar cnductance will be three times that f equivalence cnductance at any dilutin? (a) Al(SO4)3 (b) Na3PO4 (c) MgCl (d) NaCl 14. The titratin curve shwn in the parenthesis represents that fr the: / Pt

14 Chemistry: Electrchemistry-14 (a) Titratin f HCl vs NaOH (b) Titratin f CH 3COOH vs NaOH (c) Titratin f HCOOH vs KOH (d) Titratin f HCl vs NH4OH Cnductance f acid slutin 15. The cnductance that decreases with dilutin is: (a) Equivalence cnductance (b) Mlar cnductance (c) Specific cnductance (d) Inic cnductance ml f alkali added 16. Equal quantity f electricity are passed thugh three vltameters cntaining FeSO4, Fe(SO4)3 and Fe(NO3)3. Cnsider the fllwing statements: i) The amunt f irn depsited in FeSO4 and Fe(SO4)3 are equal ii) The amunt f irn depsited in Fe(NO3)3 is tw third f the amunt f irn depsited in FeSO 4. iii) The amunt f irn depsited in Fe(SO4)3 and Fe(NO3)3 is equal. Of these statements crrect is/are (a) 1 alne (b) 1 and (c) and 3 (d) 3 alne 17. The fllwing facts are available: A + B B + A ; C + B N reactin; D + A A + D. Which f the fllwing statement is crrect. (a) E E E E (b) E E E E C /C B /B A /A D /D C /C B /B A /A D /D (c) E E E E (d) E E E E C /C B /B A /A D /D C /C B /B A /A D /D 18. Salts f A (atmic weight 7), B (atmic weight = 7) and C (atmic weight 48) were electrlysed under identical cnditins using same quantity f electricity. It was fund that when.1g f A was depsited, weights f B and C depsited were.7g and 7.g. The valencies f A, B and C are respectively. (a) 3, 1 and (b) 1, 3 and (c) 3, 1 and 3 (d), 3 and 19. Cu + + e Cu; lg[cu + ] vs Ered graph is f the type shwn in figure where OA =.34V, then electrde ptential f the half cell f Cu/Cu + (.1 M) will be

15 Chemistry: Electrchemistry-15 E red A O lg[cu + ] (a) V (b) V (c).34 V (d) Nne. Standard electrde ptential data are useful fr understanding the suitability f an xidant in a redx titratin. Sme half cell reactins and their standard ptentials are given belw: MnO 4(aq). 8H (aq.) 5e Mn (aq.) 4HO(l) E = 1.51 V 3 CrO 7 (aq.) 14H (aq.) 6e Cr (aq.) 7HO(l) E = 1.38 V 3 Fe (aq.) e Fe (aq.) E =.77 V Cl (g) e Cl (aq.) E = 1.4 V Identify the nly incrrect statement regarding the quantitative estimatin f aqueus Fe(NO 3) (a) MnO 4 can be used in aqueus HCl (b) CrO 7 can be used in aqueus HCl (c) MnO 4 can be used in aqueus H SO 4 (d) CrO 7 can be used in aqueus H SO 4 1. Given E fr Cu + Cu + is +.15 V and Cu + Cu is +.5 V Calculate E fr Cu + Cu (a) +.35 V (b) +.15 V (c) +.5 V (d) +.16 V. A slutin is ne mlar in each f NaCl, CdCl, ZnCl and PbCl. T this, tin metal is added. Which f the fllwing is true? Given that, E =.16V; E =.136V Pb / Pb Sn / Sn E Cd / Cd Zn / Zn Na / Na (a) Sn can reduce Na + t Na (b) Sn can reduce Zn + t Zn (c) Sn can reduce Cd + t Cd (d) Sn can reduce Pb + t Pb 3. A certain current liberates.5g f hydrgen in hur. Hw many grams f cpper can be liberated by the same current flwing fr the same time thrugh a cpper sulphate slutin? (a) 1.7 grams (b) 15.9 g (c) 31.8g (d) 63.5 g 4. The emf f the fllwing three galvanic cells:

16 Chemistry: Electrchemistry Zn/Zn + (1M) Cu + (1M)/Cu. Zn/Zn + (.1M) Cu + (M) / Cu 3. Zn/Zn + (1M) Cu + (.1M)/Cu are represented by E 1,E,E 3. Which f the fllwing statement is true? (a) E 1 E E 3 (b) E 3 E E 1 (c) E3 E1 E (d) E E1 E3 5. Hw much will the reductin ptential f a hydrgen electrde change when its slutin initially at ph = is neutralized t ph = 7? (a) Increase by.59v (b) Decrease by.59v (c) Increase by.41v (d) Decrease by.41v SECTION II May be mre than ne chice 1. SnCl gives a precipitate with a slutin f HgCl. In this prcess HgCl (a) is reduced (b) is xidized (c) acts as an xidizing agent (d) acts as a reducing agent. Which f the fllwing statements is (are) nt crrect? (a) Reductin is always fllwed by a decrease in the xidatin number f the substance underging reductin. (b) During xidatin, a substance gains ne r mre electrns. (c) A reducing agent is the substance which itself underges reductin (d) The reactin C + O CO is a redx reactin 3. Which f the fllwing is (are) nt true fr a standard hydrgen electrde? (a) The hydrgen in cnc. is 1M. (b) H gas is nt absrbed by platinum electrde (c) The electrde wrks nly as an xidatin electrde (d E 1 H / H 4. Which ne f the fllwing will increase the vltage f the cell having the cell reactin Sn + Ag + Sn + + Ag? (a) Increase in the size f silver rd (b) Increase in the cncentratin f Sn + ins (c) Increase in the cncentratin f Ag + in (d) Decrease in the temperature f the cell 5. The standard electrde ptential f tw half cells is given belw. Ag + + e Ag; E =.8V Hg e Hg; E.78V If the tw half cells are united tgether (a) silver electrde will act as ande (b) silver electrde will act as cathde

17 Chemistry: Electrchemistry-17 (c) mercury electrde will act as ande (d) mercury electrde will act as cathde 6. Which f the fllwing statements is (are) crrect? (a) The reactivity f metals decreases in ging dwn the electrchemical series. (b) A metal can displace any ther metal placed abve it in the electrchemical series frm its salt slutin. (c) The xidizing pwer f the substances decrease frm the tp t the bttm in the electrchemical series. (d) A redx reactin is feasible when the substance having higher reductin ptential gets reduced and the ne having lwer reductin ptential gets xidized. 7. The electrde ptential f an electrde assembly depends upn the (a) nature f metal and its ins (b) cnc. f ins in slutin (c) temperature (d) nne f the abve three 8. Which f the fllwing aqueus slutin turn(s) alkaline after electrlysis? (a) NaCl (b) CuCl (c) CH 3COONa (d) K SO 4 9. When a nickel spatula is used t stir an aqueus cpper sulphate slutin (a) the slutin is stirred well withut any chemical change (b) nickel spatula gets partly xidized int Ni + ins (c) Cu + ins present in the slutin get partly reduced int Cu (d) cpper gets depsited n the spatula 1. The E.M.F. f the fllwing cell Fe(s) Fe + (.1M) Cu + (.1M) Cu is fund t be equal t.75v. The E.M.F. f the cell can be increased by (a) diluting can Fe + slutin (b) diluting Cu + slutin (c) increasing the cnc. f Fe + ins (d) increasing the cnc. f Cu Which f the fllwing reactins is (are) invlved in the rusting f irn? (a) Fe(s) Fe + (aq) + e (b) O(g) + 4H + (aq) + 4e HO(l) (c) Fe(s) + O(g) + 4H + (aq) Fe + (aq) + HO(l) (d) Fe + + e Fe(s) 1. During the recharging f a discharged lead strage battery (a) Pb changes int PbSO4 (b) PbSO4 changes int Pb and PbO (c) H SO 4 is cnsumed (d) H SO 4 is frmed 13. Which f the fllwing statements is (are) nt crrect? (a) Metallic cnductin is due t the mvement f electrns whereas the electrlytic cnductin is due t the mvement f ins. (b) Bth metallic and electrlytic cnductins invlve transfer f matter (c) Electrlytic cnductin decreases with rise in temperature

18 Chemistry: Electrchemistry-18 (d) Metallic cnductin invlves n chemical change 14. Which amng the fllwing statement(s) is/are crrect? (a) If E n is negative, H + will be reduced t H by the element A A /A (b) Cmpunds f (Zn, Na, Mg) are reduced by hydrgen (H) whereas thse f nble metals (Cu, Ag, Au) are nt reducible. (c) If E n is psitive, A n+ will be reduced t A by H A /A (d) M M n+ H + H (Pt) will be spntaneus if E n is negative M /M 15. When KCN is added t CuSO 4 slutin (a) KCN acts as a reducing agent (c) KCN acts as a cmplexing agent (b) KCN acts as n xidizing agent (d) K3[Cu(CN)4] is frmed 16. Electrlysis f water gives 11. L f hydrgen at STP at the cathde. The xygen evlved at the ande under similar cnditin is (a) 5.6 L (b).56 L (c).5 ml (d).5 ml 17. The passage f electricity thrugh certain electrlyte results in the liberatin f H gas at the cathde. The electrlyte culd be (a) CuCl(aq) (b) KCl (aq) (c) MgCl (aq) (d) AgNO 3 (aq) 18. Electrte ptential data are given belw 3 Fe (aq) e Fe (aq); E.77V 3 Al (aq) 3e Al(s); E 1.66 V Br (aq) e Br (aq); E 1.8V Based n the given data which statement/s is/are true? (a) Fe + is strnger reducing agent than Br (b) Fe + is strnger reducing agent than Al (c) Al is strnger reducing agent than Fe + (d) Br is strnger reducing agent than Al 19. The standard emf f the cell, Cd(s) CdCl (aq) AgCl(s) Ag(s) in which the cell.1m reactin is.6195 V at C and.6753 V at 5 C. The value f H f the reactin at 5 C is (a) kj/ml (b) kj/ml (c) 4 K/ml (d) 4 Kcal/ml. The standard electrde ptentials, E,E and E are respectively +.54 I /I Br /Br V, 1.9 V and.44v as the basis f given data which f fllwing is/are spntaneus Fe/ Fe

19 (a) Br I Br I (b) Fe Br Fe Br (c) Fe I Fe I (d) I Br I Br Chemistry: Electrchemistry cm 3 f.1 M AgNO3 and 5 cm 3 f a slutin that was bth.1 M in NaCl and.1m in NaBr were mixed. Which f the fllwing statements are crrect? Given that Ksp f AgCl and AgBr are and respectively. (a) Bth AgBr and AgCl are ppted ut. (b) The Ksp f AgBr is less than AgCl and s nly AgBr ppted ut (c) After mixing, the cncentratin f Cl is apprximately equal t.5 M. (d) The final cncentratin f Ag + and Br after mixing were and respectively.. The amunt f in discharged electrlysis is directly prprtinal t: (a) Resistance (b) Time (b) Current (d) Chemical equivalent f the in 3. Which are true fr a standard hydrgen electrde? (a) The hydrgen in cncentratin is 1 M (b) Temperature is 5 C (c) Pressure f hydrgen is 1 atmsphere (d) It cntains a metallic cnductr which des nt adsrb hydrgen 4. In a salt bridge, KCl fis used because (a) it is an electrlyte (b) KCl is fund in prue crystalline state in large depsits (c) it is a gd cnductr f electricity (d) if frms a gd jelly with agar-agar 5. The fllwing fur clurless salt slutins are placed in separate test tubes and strip f Cu is placed in each. Which slutin turns blue? (a) KNO3 (b) AgNO3 (c) Zn(NO 3) (d) ZnSO 4 SECTION III Cmprehensin Type Questins Write-up I A acidic slutin f Cu + salt cntaining.4gm f Cu + is electrlysed until all the cpper is depsited. The electrlysis is cntinued fr seven mre minutes with the vlumes f slutin kept at 1 ml and the current at 1. amp. 1. In the beginning f the electrlysis the substances evlved at cathde and ande are respectively (a) Cu and O (b) H and O (c) Cu and H (d) H and Cu

20 Chemistry: Electrchemistry-. During anther seven minutes f electrlysis the substances evlved at cathde and ande are respectively (a) Cu and O (b) H and O (c) Cu and H (d) Only O is evlved at cathde 3. The ttal vlume f gases evlved at STP at cathde during the entire electrlysis (a) 58.4 ml (b) 48.3 ml (c) 6.35 ml d) ml 4. The ttal vlume f gases evlved at STP at ande during the entire electrlysis (a) ml (b) 7.44 ml (c) 9.8 ml (d) 99.68ml Write-up II The standard ptential f the fllwing cell.3 V at and.1 V at Pt, H(g) HCl(aq) AgCl(s) Ag(s) 5. The cell reactin is 1 (a) H AgClAg Cl (b) H AgCl H Ag Cl (c) H AgCl Ag HCl (d) H Cl H Cl 6. The difference in the G between the tw temperature is (a) J (b) 193 J (c) 848 J (d) 369 J 7. In the abve questin the value f S is (a) 8.5 J (b) 9.5 J (c) 96.5 J (d) 1J 8. The value f H in the abve questin is (a) kj (c) kj (b) kj (d) kj Write-up III In Galvanic cell tw cells are cnnected externally thrugh a cpper wire internally thrugh a salt bridge. If salt bridge is remvel during the functining f the cell then ptential drps, with the result cell can t prduce current. 9. Salt bridge pssess (a) NH4Cl in Agar Agar (c) KNO 3 in Agar Agar (b) NH4NO3 in Agar Agar (d) All the abve 1. T increase the efficiency f the Galvanic cell fllwing shuld be charged.

21 (a) Vlume f ande shuld be increased (b) Cncentratin f electrlyte arund cathde shuld be increased (c) Cncentratin f salt in the salt bridge shuld be increased (d) All the abve 11. The salt in the salt bridge shuld have fllwing characteristics (a) Mre slubility (b) ins shuld have same transprt number (c) ins f salt shuld int interact with ins f reactin (d) All the abve 1. EMF f Galvanic cell can be calculated by.59 M.59 M (a) EE lg (b) EE lg n M n M (c).59 M.33R M EE lg (d) EE lg n M n M Chemistry: Electrchemistry-1 Write-up IV Nernest described the effect f cncentratin f electrlyte n electrde ptentials. The nernest equatin is given as E = E RT [reduced frm] in r E = E + RT [reduced frm] in nf [xidised frm] nf [xidised frm].33 RT [xidised frm] = E + lg nf [reduced frm] cmmn frm f nernst equatin at 5 C E = E +.59 [xidised frm] lg n [reduced frm] n Fr metal electrde reactin M ne M (aq) xidised frm reduced frm.59 n E = E + lg [M ] n Carefully g thrugh the abve relatinships and answer the fllwing equatins. 13. A Zn rd is dipped in a slutin f.1 M ZnSO4 slutin E fr Zn + /Zn is.76v. Its electrde ptential is (a).76v (b).8v (c) +.8V (d) +.76V 14. The hydrgen electrde is dipped in a slutin f ph 3 at 5 C the ptentialf the cell wuld be (a).177v (b).177v (c).87v (d).59v

22 Chemistry: Electrchemistry- 15. A cell cntains tw hydrgen electrdes. The negative electrde is in cntact a slutin f 1 6 M hydrgen in. The EMF f the cell is.118v at 98k. The cncentratin f H + in at the psitive electrde is (a) 1 5 M (b) 1 6 M (c) 1 4 M (d) 1 3 M 16. Electrde ptential f cpper electrde where the cncentratin f Cu + I s5m is V if E Cu + /Cu is.34 V. (a).36v (b). 36V (c) +.45 V (d).45 V Write-up V The list f standard reductin ptential values arranged in the increasing rder is cmmnly called electrchemical series r activity series. The smaller the S.R.P. values f are element, the greater is its ability t act as an reducing agent in the slutin. The greater the S.R.P. value f are element, the greater is its ability t ut as an xidizing agent in slutin. An element can reduce all thse present under it and can xidize all thse present abve, it, in electrchemical series. Read the fllwing paragraph and answer the fllwing questins. 17. Standard reductin ptentials f metal electrdes X,Y and Z are +.34V.74V and.4v respectively. Which f the fllwing is the best reducing agent? (a) X (b) Y (c) Z (d) Nne f these 18. The crrect rder f the reductin ability f metals (a) X Y Z (b) Y Z X (c) Z X Y (d) Nne f these 19. When a cpper is placed in a slutin f silver nitrate the slutin acquires blue clur. This is due t the frmatin f (a) Cu + ins (b) Cu + ins (c) sluble cmplex f cpper with AgNO 3 (d) nne f these. The reactin f Zn + + e Zn has a standard ptential f.76v. This means (a) Zn cannt replace hydrgen frm acids (b) Zn is an xidizing agent (c) Zn is a reducing agent (d) Zn + is a reducing agent. SECTION IV Subjective Questins LEVEL I 1. In refining f silver by electrlytic methd, what will be the weight f 1 gm f Ag ande if 5A current is passed fr hur. The purity f silver ande is 95% by weight.

23 Chemistry: Electrchemistry-3. A current f 1.7Å is passed thrugh 3 ml f.16 M slutin f ZnSO4 fr 3- sec with current efficiency f 9%. Find the mlarity f Zn + after the depsitin f Zn. Assume the vlume f slutin remains cnstant during electrlysis. 3. Determine the standard ptential f a cell in which the reactin C 3+ (aq) + 3Cl (aq) + 3Ag(s) 3AgCl(s) + C(s) frm the standard ptentials f the cuples Ag/AgCl, Cl (+.V), C 3+ /C + (+1.81V) and C + /C(.8V). 4. A current f amperes is passed fr 11 hurs thrugh 5 ml f M slutin f Ni(NO3) using platinum electrdes. What will be the mlarity f the slutin at the end f the electrlysis? 5. A current f.193 amp is passed thrugh 1 ml f.m NaCl fr an hur. Calculate ph f slutin after electrlysis if current efficiency is 9%. Assume n vlume change. 6. Calculate the EMF f the cell Mg (s) Mg + (.1 M) Ag + (1 1 4 M) Ag E.8V, E + Ag / Ag Mg / Mg.37V What will be the effect n EMF if cncentratin f Ag + is increased t M? 7. If and K sp f AgCl is given, find the half cell ptential f Cl (x)/agcl/ag electrde. 8. Silver is electrdepsited n a metallic vessel f surface area 8 cm by passing a current f. ampere fr 3. hurs. Calculate the thickness f silver depsited, given its density is 1.47g/cc [Atmic weight f Ag = 17.9] 9. Hw many culmbs are required t reduce 9.48 g KMnO 4 t Mn ins? (At. Masses f K = 39, Mn = 55, O = 16 amu) 1. When a current f 1.5 A was passed fr 3 minutes thrugh a slutin f a salt f a trivalent metal, 1.71 g f the metal were depsited at the cathde. Calculate the atmic mass f the metal. LEVEL II 1. The Edisn strage cell is represented as Fe(s) FeO(s) KOH(aq) NiO3(s) Ni(s) The half cell reactins are NiO3(s) + HO(l) + e NiO(s) + OH (aq) E =.4 V FeO (s) + H O (l) + e Fe (s) Fe (s) + OH E =.87V i) What is the cell reactin? ii) What is emf f the cell? Hw des it depend n the cncentratin f KOH? iii) What is the maximum amunt f electrical energy that can be btained frm ne ml f NiO3.

24 Chemistry: Electrchemistry-4. Calculate the equilibrium cnstant fr the reactin Fe + + 3I Fe + + I3. The standard reductin ptentials in acidic cnditins are.77 and.54 V respectively fr Fe 3+ /Fe + and I3 /I. 3. In a fuel cell H and O react t prduce electricity,. In the prcess H gas is xidised at the ande and O at cathde. If 67. litre f H at STP reacts in 15 minutes. What is the average current prduced? If the entire current is used fr electr depsitin f Cu frm Cu +, hw many grams f Cu are depsited Faraday is required t reduce an aqueus slutin cntaining. ml f a mixture f KMnO 4 and KCrO 7 t Mn 3 and Cr respectively. Calculate the amunt f each in the slutin. (At. Masses f K = 39, Mn = 55, Cr = 5) = 16) 5. Given the cell Cd Cd(OH)(s) NaOH (.1 ml kg -1 ) H(1 atm) Pt With E cell =. V at 98 K. If E Cd / Cd =.4 V, Calculate K sp fr Ca(OH) 6. The density f cpper is 6.94 g ml 1. Find the number f culmb needed t plate an area f 1 1 cm t a thickness f 1 cm using CuSO4 slutin as an electrlyte. Atmic weight f Cu is The standard xidatin ptential f Ni/Ni + electrde is.36 V. If this is cmbined with a hydrgen electrde in acid slutin, at what ph f the slutin will the measured e.m.f. be zer at 5 C? Assume [Ni + ] = 1M and P 1atm. 8. If we want the galvanic cell Cu(s) Cu (M 1) Cl (.1M) Pt(Cl ) 1 atm. t have an EMF f V at 5 C, what value shuld be used fr M 1, the cncentratin f Cu in? ( Ecell 1.18V) 9. a) Calculate the equilibrium cnstant fr the fllwing reactin at 5 C? Sn(s) Pb (aq) Sn (aq) Pb(s) b) If an excess f tin metal is added t 1. M Pb, what is the cncentratin f Pb at equilibrium? 1. Hw many grams f silver culd be plated ut n a serving tray by electrlysis f a slutin cntaining Ag(l) fr a perid f 8. hurs at a current f 8.46 amperes? What is the area f the tray if the thickness f the silver platting is.54 cm? Density f silver 3 is 1.5 g/ cm. LEVEL III (Judge yurself at JEE level) 1. Cpper sulphate slutin (5 ml) was electrlysed using a platinum ande and a cpper cathde. A cnstant current f ma was passed fr 16 minute. It was fund that after electrlysis, the absrbance f the slutin was reduced t 5% f its riginal value. Calculate the cncentratin f cpper sulphate in the slutin t begin with. [IIT ] H

25 Chemistry: Electrchemistry-5. Calculate the quantity f electricity that wuld be required t reduce 1.3g f nitrbenzene t aniline, if current efficiency is 5%. If the ptential drps acrss the cell is 3. vlt, hw much energy will be cnsumed? [IIT 199] 3. The fllwing electrchemical cell has been set up Pt (I) Fe, Fe (a 1) Ce, Ce (a 1)Pt (II) E 3.77B and E V Fe / Fe Ce / Ce If an ammeter is cnnected between the tw platinum electrde, predict the directin f flw f current. Will the current increase r decrease with time? [IIT ] 5. The standard reductin ptential fr Cu + /Cu is +.34V. Calculate the reductin ptential at ph = 14 fr the abve cuple. Ksp f Cu(OH) is [IIT 1996] 6. Find the slubility prduct f a saturated slutin f AgCrO4 in water at 98K if the e.m.f. f the cell Ag + Ag + (saturated AgCrO4 slutin) Ag + (.1M) Ag is.164v at 98K. [IIT 1998] 7. Fr the galvanic cell Ag AgCl(s), KCl KBr, AgBr(s) Ag.M.1M Calculate the e.m.f. generated and assign crrect plarity t each electrde fr a spntaneus prcess after taking n accunt f cell reactin at 5 C Given: K.81 ; K [IIT 199] sp spagbr 8. The standard reductin ptential f Ag + /Ag electrde at 98 K is.799v. Given that fr AgI, Ksp = , evaluate the ptential f Ag + /Ag electrde in a saturated slutin f AgI. Als calculate the standard reductin ptential f the I /AgI/Ag electrde. [IIT 1994] 9. A cell Ag Ag + Cu + Cu initially cntains 1M Ag + and 1M Cu + ins. Calculate the change in the cell ptential after the passage f 9.65 ampere f current fr 1 hur. [IIT 1999] 1. Cu + + In + Cu + + In 3+ Calculate the equilibrium cnstant. Given that E.15V Cu /Cu 3 In / In In / In E.4V E.4V [IIT 4] SECTION V Miscellaneus Questins The fllwing questins (t 5) cnsists f tw statements, ne labelled as ASSERTION (A) and REASON (R). Use the fllwing key t chse the crrect apprpriate answer. (a) (A) and (R) bth are crrect and (R) is the crrect explanatin f (A) (b) (A) and (R) bth are crrect but (R) is nt the crrect explanatin f (A)

26 Chemistry: Electrchemistry-6 (c) (A) is crrect but (R) is incrrect. (d) (A) is incrrect but (R) is crrect ASSERTION (A) 1. On increasing dilutin, the specific cnductance keep n decreasing. The standard reductin ptential values f three metallic catin A, B, C are.5.3 and 1.18 vlt respectively, s the rder f reducing pwer f metal is A C B 3. We can nt add the electrde ptential in rder t get the cell ptential if number f mles f electrns exchanged are nt same. 4. On increasing dilutin, the mlar cnductance and equivalent cnductance increases and it gets maximum value at infinite dilutin. 5. When the slpe f cell ptential with respect t temperature is zer at cnstant pressure, then S is 6. Fr the cncentratin cell, Zn(s) Zn + (aq) Zn + (aq) (C )/Zn, fr spntaneus cell reactin C1 C. REASONING (R) Because the effective number f ins per c.c. f slutin decreases. Because lwer the reductin pwer, higher will be its reducing pwer. Because the ptentials are nn-thermdynamic prperties. Because n dilutin, the number f ins f electrlyte and as well as its velcity increases. de cell Because Sp nf dt RT C Fr cncentratin cell, Ecell ln nf C1 Fr spntaneus reactin, P 7. Any cell having E cell = 5.91 vlt, will have equilibrium cnstant 1 3 at 98 K. 8. A saturated slutin f KCl is used t make salt bridge in cncentratin cells. 9. Fr the reactins, Zn Ag Zn Ag and 1 1 Zn Ag Zn Ag the cell ptential are different E cell = + ve C C 1 E Since at 98 K, Keqn = 1 cell.591 Mbility r velcities f K + and Cl are nearly same. Fr the cell reactins, Zn Ag Zn Ag and 1 1 Zn Ag Zn Ag, the free energies are different.

27 Chemistry: Electrchemistry-7 decell 1. If, then H nf Ecell d T de cell H nft Ecell d Answers t Assignments SECTION - I 1. (b). (d) 3. (d) 4. (c) 5. (c) 6. (a) 7. (b) 8. (b) 9. (b) 1. (a) 11. (a) 1. (c) 13. (b) 14. (d) 15. (c) 16. (c) 17. (b) 18. (b) 19. (a). (a) 1. (a). (d) 3. (b) 4. (d) 5. (d) SECTION - II 1. (a), (c). (b), (c) 3. (b), (c)

28 Chemistry: Electrchemistry- 4. (c), (d) 5. (b), (c) 6. (a), (d) 7. (a), (b), (c) 8. (a), (c) 9. (b), (c), (d) 1. (a), (d) 11. (a), (b), (c) 1. (b), (d) 13. (b), (c) 14. (a), (c), (d) 15. (a), (c), (d) 16. (a), (c) 17. (b), (c) 18. (a), (c) SECTION - III 19. (b), (d). (a), (b), (c) 1. (a), (c), (d). (b), (c), (d) 3. (a), (c), (d) 4. (a), (c), (d) 5. (b), (c), (d) 1. (a). (b) 3. (a) 4. (d) 5. (b) 6. (b) 7. (c) 8. (a) 9. (d) 1. (d) 11. (d) 1. (a) 13. (b) 14. (b) 15. (c) 16. (a) 17. (b) 18. (b) 19. (a). (c) SECTION - IV LEVEL I gm..154m 3..V V, increases t 3.V 7. x E.591lg Ag / Ag K sp cm C LEVEL II kj/ml g gm,.94gm M clumb M 9. (a).18, (b).315m 1. 7.g, cm LEVEL III M culmb, kj 3. decrease with time 5..5V ml 3 litre 3 7. Plarity f the cell shuld be reversed.3% 8..3V,.149V 9..1V 1. k 1 1. c SECTION - V

29 Chemistry: Electrchemistry-6 1. (a). (a) 3. (a) 4. (a) 5. (a) 6. (a) 7. (a) 8 (a) 9. (d) 1. (a)