1 8 . Identify (A) to (F) in the followig: FeSO (A) (B) + (C) + (D) 4 (C) and (D) are gases, (B) is red-brown solid, (C) can be oxidised to (D). (C) also turns C r2 O 2 /H+ solution 7 green. (B) dissolves in HCl forming deep yellow solution (E). (E) gives blue colour (F) with K [Fe(CN) ]. (D) 46 dissolves in H2O forming a well knows mineral acid called \"king of acids\". 1 9 . 2.78 g of FeSO . xH O is treated with excess of BaCl then 2.33 g of white precipitate are obtained. 42 2 Calculate the value of x. (Ba = 137, S = 32, Fe = 56, H = 1, O = 16). 2 0 . Suggest a series of reactions, using common chemicals, by which each of the following synthesis can be performed: (a) Fe(OH) from FeS 3 (b) BaCrO from BaCO and K Cr O 4 3 2 27 (c) CrCl from (NH ) Cr O 3 42 2 7 (d) MnCO from MnO 32 2 1 . A white amorphous powder (A) on heating yields a colourless, non combustible gas (B) and a solid (C). The later compound assumes a yellow colour on heating and changes to white on cooling. (C) dissolves in dilute acid and the resulting solution gives a white ppt. on adding K [Fe(CN) ] solution. (A) dissolves in 46 dilute HCl with evolution of gas, which is identical in all respect to (B). The gas (B) turns lime water milky, but the milkiness disappears with the continuous passage of gas. The solution of (A) as obtained above gives a white precipitate (D) on the addition of excess NH OH and passing H S. Another portion of the 42 solution initially gives a white precipitate (E) on the addition of NaOH solution, but dissolves on further addition of the base. Identify (A) to (E). 2 2 . A compound (A) is greenish crystalliner salt which gave the following results: (i) Adition of BaCl solution to solution of (A) results in the formation of a white ppt. (B), which is insoluble 2 in dil. HCl. (ii) On heating (A), water vapours and two oxides of sulphur, (C) and (D) are liberated leaving a red brown residue (E). (iii) (E) dissolves in warm conc. HCl to give a yellow solution (F). (iv) With H S, the solution (F) yields a pale yellow ppt. (G), which when filtered, leaves a greenish filtrate (H). 2 (v) Solution (F) on treatment with thiocyanate ions gives blood red coloured compound (I). Identify the substances from (A) to (I)
CONCEPTUAL SUBJECTIVE EXERCISE ANSWER KEY EXERCISE -4(B) 1. Ag S + 4NaCN 2Na[Ag(C N) ] + Na S 2 2 2 2 . Na[Ag(CN) ] 2 3. CuSO + KCN Cu(CN) 4 2 2Cu(CN ) 2CuCN + NC–CN (Cyanogen) 2 CuCN + KCN K [Cu(CN) ] 34 K [Cu(CN) ] 3K+ [Cu(CN) ]–3 H2S no ppt 34 4 4 . Due to presence of unpaired electron and d-d transition 5 . KMnO4 oxidizes HCl to Cl2 6 . Na Cr O is deliquescent in nature 2 27 7 . Pt+4 is thermo dynamically more stable than Ni+4. 8 . TiCl4 + H2O Ti(OH)4 + 4HCl 1 0 . Due to strong metallic bond strength 1 1 . (a) Ag+ = 5d10 n=0 Ti+4 = 3s2 3p6 n=0 Co+2 = [Ar] 3d7 n=3 (b) Co+2 attracted by a magnetic field due to presence of unpaired electron. 12. (i) Cr O –2 + 6Fe+2 14H 2Cr+3 + 6Fe+3 27 + 7H O 2 (ii) Cr O –2 + 6I– + 14H+ 2Cr+3 + 3I 27 2 + 7H O 2 1 3 . (a) 2MnO – + 16H + 10Fe+2 4 2Mn+2 + 8H O + 10 Fe+3 2 (b) 2MnO – + 5SO + 2H O 4 2 2 5SO –2 + 2Mn+2 + 4H 4 (c) 2MnO – + 16H +5C O –2 4 24 2Mn+2 + 8H O + 10CO 22 14. (a) AgCl + 2NH OH [Ag(NH ) ] +2H O 4 32 2 (b) Hg Cl + NH Hg + HgNH Cl+NH Cl 22 3 24 (c) HgCl + 2NH aq. Hg(NH )Cl + NH Cl 2 3 2 4 Mercury aminochlordie 1 5 . In acidic medium 90 Equivalent weight of oxalic acid = = 45 2
158 Equivalent weight of KMnO = = 31.6 45 1 6 . (i) MnO + KOH+O 2K MnO + 4H O (ii) 2 2 2 4 2 pot manganate Cr 2 O 2 +3H S + 8H+ 2Cr3+ 7H O +3S 7 2 2 (iii) 2Mn O +I– + HO 2MnO +2OH– + IO 1 4 2 2 3 1 7 . Solution changes to light green due to reduction of Fe3+ to Fe2+ FeCl + H S 2FeCl +2HCl + S 32 2 1 8 . (A) : FeSO (B) : Fe O (C) : SO (D) : SO (E) : FeCl (F) : KFeIII [FeII(CN) , Prussian blue. 4 23 2 3 3 6 19. x = 7 2 0 . (a) FeS H2SO4 FeSO4 H2S NaOH + H2O2 Fe(OH)3 CO2 HCl (b) BaCO3 BaCl2 BaCrO4 KOH (c) H2O, N2 Conc. HCl CrCl3 ,conc. HCl Cl2 (d) Na2CO3 MnCO3 2 1 . (A) : ZnCO (B) : CO (C) : ZnO (D) : Zn(OH) (E) : Na ZnO 32 2 22 2 2 . (A) : FeSO · 7H O (B) : BaSO (C) : SO (D) : SO (E) : Fe O (F) : FeCl (G) : S (H) : FeCl (I) : Fe(CNS) 42 4 2 3 23 3 23
REMARK : Q. 1, 3, 6, 7, 8, 9 10, 12, 13 (THESE ARE F-BLOCK) EXERCISE–05 [A] PREVIOUS YEARS QUESTIONS 1 . The radius of La3+ is 1.06Å, which of the following given values will be closest to the radius of Lu3+ (At no. of Lu = 71, La = 57)- [AIEEE-2003] (1) 1.6 Å (2) 1.4 Å (3) 1.06 Å (4) 0.85 Å 2 . What would happen when a solution of potassium chromate is treated with an excess of dilute nitric acid - (1) Cr3+ and C r O 2 – are formed [AIEEE-2003] 7 2 (2) C r2 O 2 – and H2O are formed 7 (3) Cr O 2 – is reduced to +3 state of Cr 7 2 (4) Cr2 O72– is oxidised to +7 state of Cr 3 . Cerium (Z = 58) is an important member of the lanthanoids. Which of the following statements about cerium is incorrect - [AIEEE-2004] (1) Cerium (IV) acts as an oxidising agent (2) The +3 oxidation state of cerium is more stable than the +4 oxidation state (3) The +4 oxidation state of cerium is not known in solutions (4) The common oxidation states of cerium are +3 and +4 4 . Excess of KI reacts with CuSO4 solution and then Na2S2O3 solution is added to it. Which of the statements is incorrect for this reaction : [AIEEE-2004] (1) Evolved I2 is reduced (2) CuI2 is formed (3) Na2S2O3 is oxidised (4) Cu2I2 is formed 5 . Calomel on reaction with NH4OH gives [AIEEE-2004] [AIEEE-2005] (1) HgNH2Cl (2) NH2–Hg–Hg–Cl (3) Hg2O (4) HgO 6 . The lanthanoid contraction is responsible for the fact that - (1) Zr and Y have about the same radius (2) Zr and Nb have similar oxidation state (3) Zr and Hf have about the same radius (4) Zr and Zn have similar oxidation state 7 . Lanthanoid contraction is caused due to [AIEEE-2006] (1) the same effective nuclear charge from Ce to Lu (2) the imperfect shielding on outer electrons by 4f electrons from the nuclear charge (3) the appreciable shielding on outer electrons by 4f electrons from the nuclear charge (4) the appreciable shielding on outer electrons by 5d electrons from the nuclear charge 8 . Identify the incorrect statement among the following- [AIEEE-2007] (1) d-block elements show irregular and erratic chemical properties among themselves (2) La and Lu have partially filled d-orbitals and no other partially filled orbitals (3) The chemistry of various lanthanoids is very similar (4) 4f and 5f-orbitals are equally shielded 9 . The actinoids exhibits more number of oxidation states in general than the lanthanoids. This is because - (1) The 5f-orbitals are more buried than the 4f-orbitals [AIEEE-2007] (2) There is a similarly between 4f-and-5f in the their angular part of the wave function (3) The actinoids are more reactive than the lanthanoids (4) The 5f-orbitals extend further from the nucleus than the 4f-orbitals 1 0 . Larger number of oxidation states are exhibited by the actinides than those by the lanthanides, the main reason being [AIEEE-2008] (1) 4f orbitals more diffused than the 5f orbitals (2) lesser energy difference between 5f and 6d than between 4f and 5d orbitals (3) more energy difference between 5f and 6d than between 4f and 5d orbitals (4) more reactive nature of the actinides than the lanthanides
1 1 . In context with the transition elements, which of the following statements is incorrect ? [AIEEE-2009] (1) In the highest oxidation states of the first five transition elements (Sc to Mn), all the 4s and 3d electrons are used for bonding. (2) Once the d5 configuration is exceeded, the tendency to involve all the 3d electrons in bonding decreases. (3) In addition to the normal oxidation states, the zero oxidation state is also shown by these elements in complexes. (4) In the highest oxidation states, the transition metal show basic character and form cationic complexes. 1 2 . Knowing that the chemistry of lanthanoids (Ln) is dominated by its +3 oxidation state, which of the following statements is incorrect ? [AIEEE-2009] (1) Ln(III) compounds are generally colourless (2) Ln(III) hydroxides are mainly basic in character (3) Because of the large size of the Ln(III) ions the bonding in its compounds is predominently ionic in character (4) The ionic sizes of Ln(III) decrease in general with increasing atomic number 1 3 . In context of the lanthanoids, which of the following statements is not correct ? [AIEEE-2011] (1) Because of similar properties the separation of langhanoids is not easy (2) Availability of 4f electrons results in the formation of compounds in +4 state for all the members of the series (3) There is a gradual decrease in the radii of the members with increasing atomic number in the series (4) All the members exhibit +3 oxidation state 1 4 . Iron exhibits +2 and +3 oxidation states. Which of the following statements about iron is incorrect ? [AIEEE-2012] (1) Ferrous compounds are more easily hydrolysed than the corresponding ferric compounds. (2) Ferrous oxide is more basic in nature than the ferric oxide. (3) Ferrous compounds are relatively more ionic than the corresponding ferric compounds. (4) Ferrous compounds are less volatile than the corresponding ferric compounds. 1 5 . Which of the following arrangements does not represent the correct order of the property stated against it ? (1) V2+ < Cr2+ < Mn2+ < Fe2+ : paramagnetic behaviour [JEE MAINS-2013] (2) Ni2+ < Co2+ < Fe2+ < Mn2+ : ionic size (3) Co3+ < Fe3+ < Cr3+ < Sc3+ : stability in aqueous solution (4) Sc < Ti < Cr < Mn : number of oxidation states 1 6 . Four successive members of the first row transition elements are listed below with atomic numbers. Which one of them is expected to have the highest E0 value ? [JEE MAINS-2013] M3 / M2 (1) Cr(Z = 24) (2) Mn(Z = 25) (3) Fe (Z = 26) (4) Co(Z = 27) 1 7 . Expermentally it was found that a metal oxide has formula M0.98O. Metal M, is present as M2+ and M3+ in its oxide. Fraction of the metal which exists as M3+ would be :- [JEE MAINS-2013] (1) 7.01% (2) 4.08% (3) 6.05% (4) 5.08 PREVIOUS YEARS QUESTIONS ANSWER KEY EXERCISE -5 [A] Que. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Ans 4 2 3 2 1 3 2 4 4 2 4 1 2 1 1 4 2
EXERCISE–05 [B] PREVIOUS YEARS QUESTIONS 1 . Anhydrous ferric chloride is prepared by – [IIT 2002] (A) Heating hydrated ferric chloride at a high temperature in a steam of air (B) Heating metallic iron in a steam of dry chlorine gas (C) Reaction of ferric oxide with HCl (D) Reaction of metallic iron with HCl 2 . When MnO is fused with KOH and KNO , a coloured compound is formed, the product and its colour is – 22 [IIT 2003] (A) K MnO , green (B) KMnO , purple (C) Mn O , brown (D) Mn O , black 24 4 23 34 3 . (NH ) Cr O on heating gives a gas, which is also given by – [IIT- 2004] 42 2 7 (A) Heating NH NO (B) Heating NH NO (C) Mg N + H O (D) Na + H O 42 43 32 2 22 4 . The pair of compounds having metals in their highest oxidation state is – [IIT-2004] (A) MnO2, FeCl3 (B) [MnO4]–, CrO2Cl2 (C) [Fe(CN)6]3–, [Co(CN)3] (D) [NiCl4]2–, [CoCl4]– 5 . The compound having tetrahedral geometry is – [IIT- 2004] (A) [Ni(CN)4]2– (B) [Pd(CN)4]2– (C) [PdCl4]2– (D) [NiCl4]2– [IIT- 2004] 6 . Spin only magnetic moment of the compound Hg[Co(SCN)4] is – (A) 3 (B) 15 (C) 24 (D) 8 7 . Which pair of compounds is expected to show similar colour in aqueous medium? [IIT- 2004] (A) FeCl3 and CuCl2 (B) VOCl2 and CuCl2 (C) VOCl2 and FeCl2 (D) FeCl2 and MnCl2 8 . NiCl2 in the presence of dimethyl glyoxime (DMG) gives a complex which precipitates in the presence of NH4OH, giving a bright red colour. [IIT- 2004] (a) Draw its structure and show H-bonding (b) Give oxidation state of Ni and its hybridisation (c) Predict whether it is paramagnetic or diamagnetic. 9 . A solution of a metal ion when treated with KI gives a red precipitate which dissolves in excess KI to give a colourless solution. Moreover, the solution of metal ion on treatment with a solution of cobalt(II) thiocyanate gives rise to a deep blue crystalline precipitate. The metal ion is – [IIT- 2005] (A) Pb2+ (B) Hg2+ (C) Cu2+ (D) Co2+ 1 0 . Write balanced chemical equation for developing a black and white photographic film. Also give reason why the solution of sodium thiosulphate on acidification turns milky white and give balance equation of this reaction – [IIT- 2005] 1 1 . Fe3+ SNC –(excess) A F – (excess) B [IIT- 2005] Blood red Colourless Identify A and B. (i) Write IUPAC name of A and B. (ii) Find out spin only magnetic moment of B 1 2 . Consider a titration of potassium dichromate solution with acidified Mohr's salt solution using diphenylamine as indicator. The number of moles of Mohr's salt required per mole of dichromate is – [IIT- 2007] (A) 3 (B) 4 (C) 5 (D) 6
13. Match the column [IIT- 2007] Column-I Column-II (A) O – O2 + O 2 – (p) redox reaction 2 2 (B) CrO 2 – + H+ (q) one of the products has trigonal planar structure 4 (C) M nO – + N O 2– + H+ (r) dimeric bridged tetrahedral metal ion 4 (D) N O – + H2SO4 + Fe2+ (s) disproportionation 3 1 4 . Upon treatment with ammonical H2S , the metal ion that precipitates as a sulphide is - [IIT-2013] (A) Fe(III) (B) Al(III) (C) Mg(II) (D) Zn (II) PREVIOUS YEARS QUESTIONS ANSWER KEY EXERCISE -5 [B] 7. B 1. B 2. A 3. A 4. B 5. D 6. B 8 . (a) Structure of the complex is Hydrogen bonding O–............. H—O H3C–C=N N = C–CH3 Ni H3C–C=N N = C–CH3 O—H ............ O– Hydrogen bonding (b) The oxidation state of Ni in this compouind is +2 and it shows dsp2 hybridisation. (c) Since the coordination number of Ni in this complex is 4. According to crystal field theory it is diamagnetic in nature 9. (B) 1 0 . (i) The following reactions are used in developing the photographic film. OH O 2AgBr + 2Ag + 2HBr + OH O Quinone Hydroquinone (developer) AgBr + 2Na S O Na [Ag(S O ) ] + NaBr 22 3 3 2 32 hypo solution soluble (ii) Aqueous solution of sodium thiosulphate (Na S O ) on acidification gives milky white turbidity of collodial 22 3 sulphur. Na S O + 2 H ). 2Na+ + H SO + S (colloidal sulphur) 22 3 (aq 23 1 1 . (a) A : [Fe(SCN)(H O) ]2+ (Pentaaquathiocyanatoferrate(III)ion) B : [FeF ]3– (Hexafluoroferrate(III) ion) 25 6 (b) 5.92 BM 12. D 13. (A) p,s ; (B) r ; (C) p,q ; (D) p 14. (D)
EXERCISE-01 CHECK YOUR GRASP SELECT THE CORRECT ALTERNATIVE (ONLY ONE CORRECT ANSWER) 1 . If a spoon of copper metal is placed in a solution of ferrous sulphate :- (A) Cu will precipitate out (B) iron will precipitate (C) Cu and Fe will precipitate (D) no reaction will take place 2 . During discharge of a lead storage cell the density of sulphuric acid in the cell :- (A) increasing (B) decreasing (C) remains unchanged (D) initially increases but decreases subsequently 3 . Which of the following represents the reduction potential of silver wire dipped into 0.1 M AgNO3 solution at 25°C :- (A) E°red (B) (E°red + 0.059) (C) (E°ox – 0.059) (D) (E°red – 0.059) 4 . If the solution of the CuSO4 in which copper rod is immersed is diluted to 10 times, the electrode reduction potential. (T = 298 K) :- (A) increases by 0.030 volt (B) decreases by 0.030 volt (C) increases by 0.059 volt (D) decreases by 0.0059 volt 5 . The oxidation potential of a hydrogen electrode at pH = 1 is (T = 298 K) :- (A) 0.059 volt (B) 0 volt (C) –0.059 volt (D) 0.59 volt 6 . The electrode potential becomes equal to standard electrode potential when reactants and products concen- tration ratio is :- (A) equal to 1 (B) greater than 1 (C) less than 1 (D) none of the above 7 . The reduction potential values are given below Al3+ / Al = – 1.67 volt, Mg2+ / Mg = –2.34 volt Cu2+ / Cu = + 0.34 volt I2 / 2l– = + 0.53 volt. Which one is the best reducing agent ? (A) Al (B) Mg (C) Cu (D) I2 8 . When iron is rusted, it is :- (A) reduced (B) oxidised (C) evaporated (D) decomposed 9 . The reference electrode is made from which of the following :- (A) ZnCl2 (B) CuSO4 (C) Hg2Cl2 (D) HgCl2 1 0 . Given standard electrode potentials : Fe3+ + 3e– Fe ; E° = –0.036 volt Fe2+ + 2e– Fe ; E° = –0.440 volt The standard electrode potential E° for Fe3+ + e– Fe2+ is :- (A) –0.476 volt (B) –0.404 volt (C) 0.440 volt (D) 0.772 volt 1 1 . The reduction potential of a hydrogen electrode at pH 10 at 298 K is : (p = 1 atm) (A) 0.51 volt (B) 0 volt (C) –0.591 volt (D) 0.059 volt 1 2 . The emf of the cell, Ni|Ni2+ (1.0 M)||Ag+ (1.0 M)|Ag[E° for Ni2+/Ni = – 0.25 volt, E° for Ag+/Ag = 0.80 volt] is given by : [E° for Ag+ / Ag = 0.80 volt] (A) –0.25 + 0.80 = 0.55 volt (B) –0.25 – (+0.80) = –1.05 volt (C) 0 + 0.80 – (–0.25) = + 1.05 volt (D) –0.80 – (+0.25) = –0.55 volt 1 3 . 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 aluminium and copper nitrate (C) The solution becomes blue (D) There is no reaction 1 4 . E° (Ni2+ / Ni) = – 0.25 volt, E° (Au3+ / Au) = 1.50 volt. The emf of the voltaic cell Ni|Ni2+ (1.0 M)||Au3+ (1.0 M)| Au is :- (A) 1.25 volt (B) –1.75 volt (C) 1.75 volt (D) 4.0 volt
1 5 . When the electric current is passed through a cell having an electrolyte, the positive ions move towards cathode and negative ions towards the anode. If the cathode is pulled out of the solution :- (A) the positive and negative ions will move towards anode (B) the positive ions will start moving towards the anode while negative ions will stop moving (C) the negative ions will continue to move towards anode while positive ions will stop moving (D) the positive and negative ions will start moving randomly 1 6 . The oxidation potentials of Zn, Cu, Ag, H2 and Ni are 0.76, –0.34, –0.80, 0.00, 0.25 volt respectively. Which of the following reactions will provide maximum voltage :- (A) Zn + Cu2+ Cu + Zn2+ (B) Zn + 2Ag+ 2Ag + Zn2+ (C) H2 + Cu2+ 2H+ + Cu (D) H2 + Ni2+ 2H+ + Ni 1 7 . Which one of the following will increase the voltage of the cell : (T = 298 K) Sn + 2 Ag+ Sn2+ + 2 Ag (A) increase in the size of silver rod (B) increase in the concentration of Sn+2 ions (C) increase in the concentration of Ag+ ions (D) none of the above 1 8 . A chemist wants to produce Cl2 (g) from molten NaCl. How many grams could be produced if he uses a steady current of 2 ampere for 2.5 minutes :- (A) 3.55 g (B) 1.775 g (C) 0.110 g (D) 0.1775 g 1 9 . Consider the reaction : (T = 298 K) Cl2 (g) + 2Br– (aq) 2Cl– (aq) + Br2 (aq.) The emf of the cell, when [Cl–] = [Br2] = [Br–] = 0.01 M and Cl2 gas is 1 atm pressure, will be (E° for the above reaction is = 0.29 volt) :- (A) 0.54 volt (B) 0.35 volt (C) 0.24 volt (D) –0.29 volt 2 0 . Three faradays of electricity was passed through an aqueous solution of iron (II) bromide. The mass of iron metal (at. mass 56) deposited at the cathode is :- (A) 56 g (B) 84 g (C) 112 g (D) 168 g 2 1 . The standard emf for the cell reaction Zn + Cu2+ Zn2+ + Cu is 1.10 volt at 25°C. The emf for the cell reaction when 0.1 M Cu2+ and 0.1 Zn2+ solutions are used at 25°C is :- (A) 1.10 volt (B) 0.110 volt (C) –1.10 volt (D) –0.110 volt 2 2 . Three moles of electrons are passed through three solutions in succession containing AgNO3, CuSO4 and AuCl3 respectively. The molar ratio of amounts of cations reduced at cathode will be :- (A) 1 : 2 : 3 (B) 2 : 1 : 3 (C) 3 : 2 : 1 (D) 6 : 3 : 2 2 3 . The emf of the cell involving the following reaction, 2 Ag+ + H2 2 Ag + 2H+ is 0.80 volt. The standard oxidation potential of silver electrode is :- (A) –0.80 volt (B) 0.80 volt (C) 0.40 volt (D) –0.40 volt 2 4 . For the electrochemical cell, M|M+||X–|X, E°M+/M = 0.44 V and E°X/X– = 0.33 V. From this data we can deduce that :- (A) M + X M+ + X– is the spontaneous reaction (B) M+ + X– M + X is the spontaneous reaction (C) Ecell = 0.77 V (D) Ecell = –0.77 V 2 5 . For the net cell reaction of the cell Zn(s)|Zn2+||Cd2+|Cd(s) G° in kilojules at 25°C is (E°cell = 0.360 V):- (A) 112.5 (B) 69.47 (C) –34.73 (D) –69.47 2 6 . How many faradays are required to reduce one mol of MnO4– to Mn2+:- (A) 1 (B) 2 (C) 3 (D) 5 2 7 . Cu+ + e– Cu, E° = x1 volt ; Cu2+ + 2e– Cu, E° = x2 volt, then for Cu2+ + e– Cu+, E° (volt) will be : (A) x1 – 2x2 (B) x1 + 2x2 (C) x1 – x2 (D) 2x2 – x1
2 8 . Zn|Zn2+ (C1)||Zn2+ (C2)|Zn. for this cell G is negative if :- (A) C1 = C2 (B) C1 > C2 (C) C2 > C1 (D) None 29. Pt H2 H H H2 Pt (where p1 and p2 are pressure) cell reaction will be spontaneous if :- (p1 ) (1M ) (1M ) (p2 ) (A) p1 = p2 (B) p1 > p2 (C) p2 > p1 (D) p1 = 1 atm 3 0 . Pt (H2 ) pH 2|| pH 3 (H2 ) Pt . The cell reaction for the given cell is :- 1 atm 1 atm (A) spontaneous (B) non-spontaneous (C) equilibrium (D) none is correct 3 1 . M2+ + 2e M. 0.275 g of metal M is deposited at the cathode due to passage of 1A of current for 965 s. Hence atomic weight of the metal M is :- (A) 27.5 (B) 55.0 (C) 110.0 (D) 13.75 3 2 . In an electrochemical cell that function as a voltaic cell :- (A) electrons move from the cathode to the anode (B) electrons move through a salt-bridge (C) electrons can move either from the cathode to the anode or from the anode to the cathode (D) reduction occurs at the cathode 3 3 . A certain metal salt solution is electrolysed in series with a silver coulometer. The weight of silver and the metal deposited are 0.5094 g and 0.2653 g. Calculate the valency of the metal if its atomic weight is nearly that of silver. (A) .1 (B) 2 (C) 3 (D) 4 3 4 . The cell Pt (H2) (1 atm) |H+ (pH = ?), I– (a = 1) AgI(s), Ag has emf, E298 K = 0. The electrode potential for the reaction AgI + e– Ag + I is –0.151 volt. Calculate the pH value :- (A) 3.37 (B) 5.26 (C) 2.56 (D) 4.62 3 5 . Using the information in the preceding problem, calculate the solubility product of AgI in water at 25°C [E°(Ag+,Ag) = +0.799 volt] :- (A) 1.97 × 10–17 (B) 7.91 × 10–17 (C) 1.79 × 10–17 (D) 9.17 × 10–17 3 6 . If same quantity of electricity is passed through CuCl and CuSO4, the ratio of the weights of Cu deposited from CuSO4 and CuCl is :- (A) 2 : 1 (B) 1 : 2 (C) 1 : 1 (D) 4 : 1 3 7 . For Zn2+/ Zn, E° = –0.76 V, for Ag+ / Ag, E° = 0.799 V. The correct statement is :- (A) the reaction Zn getting reduced Ag getting oxidized is spontaneous (B) Zn undergoes reduction and Ag is oxidized (C) Zn undergoes oxidation and Ag+ gets reduced (D) No suitable answer 3 8 . The oxidation potential of a hydrogen electrode at pH = 10 and PH2 = 1 is :- (A) 0.51 V (B) 0.00 V (C) + 0.59 V (D) 0.059 V CHECK YOUR GRASP ANSWER KEY EXERCISE -1 Que. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Ans . D B D B A A B B C D C C D C D Que. 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Ans . B C C B B A D A B D D D C B B Que. 31 32 33 34 35 36 37 38 Ans . B D B C B B C C
EXERCISE–02 BRAIN TEASERS SELECT THE CORRECT ALTERNATIVES (ONE OR MORE THEN ONE CORRECT ANSWERS) 1 . What a lead storage is discharged :- (A) PbSO4 is formed (B) Pb is formed (C) SO2 is consumed (D) H2SO4 is consumed 2 . The standard emf of the cell, Cd (s)|CdCl2 (aq) (0.1 M)||AgCl (s)|Ag (s) in which the cell reaction is, Cd (s) + 2 AgCl (s) 2 Ag (s) + Cd+2 (aq) + 2Cl– (aq) is 0.6915 V at 0°C and 0.6753 V at 25°C. The H of the reaction at 25°C is :- (A) –176 kJ (B) –234.7 kJ (C) +123.5 kJ (D) –167.26 kJ 3 . A current of 2.68 A is passed for one hour through an aqueous solution of CuSO4 using copper electrodes. Select the correct statement (s) from the following :- (A) increase in mass of cathode = 3.174 g (B) decrease in mass of anode = 3.174 g (C) no change in masses of electrodes (D) the ratio between the change of masses of cathode and anode is 1 : 2 4 . Any redox reaction would occur spontaneously, if :- (A) the free energy change (G) is negative (B) the (G) is positive (C) the cell e.m.f. (E°) is negative (D) the cell e.m.f. is positive 5 . Fe is reacted with 1.0 M HCl. E° for Fe/Fe2+ = +0.34 volt. The correct observation (s) regarding this reaction is / are :- (A) Fe will be oxidised to Fe2+ (B) Fe2+ will be reduced to Fe (C) since e.m.f. is positive, the reaction shall occur (D) since e.m.f. is positive, the reaction shall not occur 6 . An acidic solution of copper (II) sulphate containing some contaminations of zinc and iron (II) ions was electrolysed till all the copper is deposited. If electrolysis is further continued for sometime, the product liberated at cathode is :- (A) Fe (B) Zn (C) H2 (D) Alloy of Zn and Fe 7 . A current of 9.65 ampere is passed through the aqueous solution NaCl using suitable electrodes for 1000 s. The amount of NaOH formed during electrolysis is :- (A) 2.0 g (B) 4.0 g (C) 6.0 g (D) 8.0 g 8. The potential of the Daniel cell, Zn ZnSO4 CuSO4 Cu was reported by Buckbee, Surdzial and Metz as (1M ) (1M ) E°= 1.1028 – 0.641 × 10–3 T + 0.72 × 10–5 T2 , where T is the celsius temperature. Calculate S° for the cell reaction at 25°C :- (A) –45.32 EU (B) –34.52 EU (C) –25.43 EU (D) –54.23 EU 9 . Using the data in the preceding problem, calculate the equilibrium constant of the reaction at 25°C. Zn + Cu++ Zn++ + Cu, K [Zn2 ] = [Cu2 ] (A) 8.314 × 1024 (B) 4.831 × 1031 (C) 8.314 × 1036 (D) 4.831 × 1044 1 0 . The standard electrode potential (reduction) of Ag+|Ag is 0.800 V at 25°C. Its electrode potential in a solution containing 10–3 M ion of Ag+ ions is :- (A) 0.623 V (B) –0.977 V (C) 0.892 V (D) 1.246 V
1 1 . The number of faradays required to produce one mole of water from hydrogen - oxygen fuel cell containing aqueous alkali as electrolyte is :- (A) 1 (B) 3 (C) 2 (D) 4 1 2 . The solubility product of silver iodide is 8.3 × 10–17 and the standard potential (reduction) of Ag, Ag+ electrode is +0.800 volts at 25°C. The standard potential of Ag, AgI / I – electrode (reduction) from these data is :- (A) –0.30 V (B) +0.15 V (C) +0.10 V (D) –0.15 V 1 3 . The standard electrode potentials (reduction) of Pt/Fe3+, Fe+2 and Pt/Sn4+, Sn+2 are +0.77 V and 0.15 V respectively at 25°C. The standard EMF of the reaction Sn4+ + 2 Fe2+ Sn2+ + 2Fe3+ is :- (A) –0.62 V (B) –0.92 V (C) +0.31 V (D) +0.85 V 1 4 . The standard reduction potential E° of the following systems are :- System E°(volts) (i) MnO4– + 8H+ + 5e– Mn2+ + 4H2O 1.51 (ii) Sn4+ + 2e– Sn2+ 0.15 (iii) Cr2O72– + 14H+ + 6e– 2Cr3+ + 7H2O 1.33 (iv) Ce4+ + e– Ce3+ 1.61 The oxidising power of the various species decreases in the order : (A) Ce4+ > Cr2O72– > Sn4+ > MnO4– (B) Ce4+> MnO4– > Cr2O72– > Sn4+ (C) Cr2O72– > Sn4+ > Ce4+ > MnO4– (D) MnO4– > Ce4+ > Sn4+ > Cr2O72– 1 5 . The e.m.f. of the following cell Ni(s) / NiSO4 (1.0 M) || H+ (1.0 M)|H2 (1 atm), Pt at 25°C is 0.236 V. The electrical energy which can be produced is :- (A) 22.73 kJ (B) 45.55 kJ (C) 19.30 kJ (D) 23.60 kJ 1 6 . The reduction potential of a hydrogen electrode at pH = 10, at 25°C is :- (A) –0.59 V (B) –0.0591 V (C) zero (D) –0.591 V 1 7 . The reduction potential of a half-cell consisting of a Pt electrode immersed in 1.5 M Fe2+ and 0.015 M Fe3+ solution at 25°C is ( E0 = 0.770 V) : Fe3+/Fe2+ (A) 0.652 V (B) 0.88 V (C) 0.710 V (D) 0.850 V 18. Consider the cell H2 (Pt) H3O(aq) Ag Ag. The measured EMF of the cell is 1.023 V. What is the value of 1atm pH 5.5 xM x? E0Ag+, Ag = + 0.799 V. [T = 25°C] (A) 2 × 10–2 M (B) 2 × 10–3 M (C) 1.5 × 10–3 M (D) 1.5 × 10–2 M 1 9 . Hg2Cl2 is produced by the electrolytic reduction of Hg2+ ion in presence of Cl– ion is 2Hg2++ 2Cl– + 2e Hg2Cl2. Calculate the current required to have a rate production of 44 g per hour of Hg2Cl2 . [Atomic weight of Hg = 200.6] :- (A) 5 ampere (B) 4 ampere (C) 6.5 ampere (D) 3.5 ampere 2 0 . The ionization constant of a weak electrolyte is 25 × 10–6 while the equivalent conductance of its 0.01 M solution is 19.6 S cm2 eq–1. The equivalent conductance of the electrolyte at infinite dilution (in S cm2 eq–1) will be :- (A) 250 (B) 196 (C) 392 (D) 384
2 1 . Which of the following curve represents the variation of M with C for AgNO3 ? M M M M (A) (B) (C) (D) C C C C 2 2 . Four moles of electrons were transferred from anode to cathode in an experiment on electrolysis of water. The total volume of the two gases (dry and at STP) produced will be approximately (in litres) :- (A) 22.4 (B) 44.8 (C) 67.2 (D) 89.4 2 3 . Equivalent conductance of BaCl2, H2SO4 & HCl at infinite dilution are A1 , A2 & A3 respectively. Equivalent conductance of BaSO4 solution is : (A) A1 + A2 – 2 A3 (B) A1 + A2 + A3 (C) A1 + A2 – A3 (D) A1 – A2 + A3 2 4 . Salts of A (atomic weight = 7), B (atomic weight = 27) and C (atomic weight = 48) were electrolysed under identical conditions using the same quantity of electricity. It was found that when 2.1 g of A was deposited, the weights of B and C deposited were 2.7g and 7.2 g. The valencies of A, B and C respectively are :- (A) 3, 1 and 2 (B) 1, 3 and 2 (C) 3, 1 and 3 (D) 2, 3 and 2 2 5 . During electrolysis of an aqueous solution of CuSO4 using copper electrodes, if 2.5 g of Cu is deposited at cathod, then at anode :- (A) 890 mL of Cl2 at STP is liberated (B) 445 mL of O2 at STP is liberated (C) 2.5 g of copper is deposited (D) a decrease of 2.5 g of mass takes place 2 6 . The cost at 5 paise/KWH of operating an electric motor for 8 hours which takes 15 amp at 110 V is :- (A) Rs. 66 (B) 66 paise (C) 37 paise (D) Rs. 6.60 2 7 . When an aqueous solution of lithium chloride is electrolysed using graphite electrodes :- (A) Cl2 is liberated at the anode (B) Li is deposited at the cathode (C) as the current flows, pH of the solution around the cathode remains constant (D) as the current flows, pH of the solution around the cathode decreases 2 8 . A silver wire dipped in 0.1 M HCl solution saturated with AgCl develops a potential of –0.25 V. If E°Ag/Ag+ = –0.799 V, the Ksp of AgCl in pure water will be :- (A) 2.95 × 10–11 (B) 5.1 × 10–11 (C) 3.95 × 10–11 (D) 1.95 × 10–11 2 9 . Consider the reaction of extraction of gold from its ore Au + 2CN– (aq.) + 1 1 H2O Au(CN)2– + OH– 4 O2 (g) + 2 Use the following data to calculate G° for the reaction Kf {Au(CN)2–} = X : E° = + 0.41 volt O2 + 2H2O + 4e– 4OH– : E° = + 1.5 volt Au3+ + 3e– Au Au3+ + 2e– Au+ : E° = + 1.4 volt (A) –RT ln X + 1.29 F (B) –RT ln X – 2.11 F 1 (D) –RT ln X – 1.29 F (C) –RT ln + 2.11 F X
3 0 . Consider the following Galvanic cell :- H2(g) Voltmeter Cl2(g) K NO–3 Pt(s) HCl HCl Anode Cathode By what value the cell voltage when concentration of ions in anodic and cathodic compartments both in- creased by factor of 10 at 298 K. (A) +0.0591 (B) –0.0591 (C) –0.1182 (D) 0 3 1 . For the fuel cell reaction 2H2(g) + O2(g) 2H2O() ; fH°298(H2O, ) = – 285.5 kJ/mol What is S°298 for the given fuel cell reaction ? E° = 1.23 V Given : O2(g) + 4H+(aq) + 4e– 2H2O() (A) –0.322 J/K (B) –0.635 kJ/K (C) 3.51 kJ/K (D) –0.322 kJ/K 3 2 . The resistance of 0.5 M solution of an electrolyte in a cell was found to be 50 . If the electrodes in the cell are 2.2 cm apart and have an area of 4.4 cm2 then the molar conductivity (in S m2 mol–1) of the solution is :- (A) 0.2 (B) 0.02 (C) 0.002 (D) none of these 3 3 . The dissociation constant of n-butyric acid is 1.6 × 10–5 and the molar conductivity at infinite dilution is 380 × 10–4 Sm2mol–1. The specific conductance of the 0.01 M acid solution is :- (A) 1.52 × 10–5 Sm–1 (B) 1.52 × 10–2 Sm–1 (C) 1.52 × 10–3 Sm–1 (D) none BRAIN TEASERS ANSWER KEY EXERCISE -2 Que. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 An s . A,D D A,B A,D A,C C B D C A C D A B B Que. 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Ans . D A A A C A C C B D B A B A C Que. 31 32 33 Ans . D C B
EXERCISE–03 MISCELLANEOUS TYPE QUESTIONS TRUE / FALSE 1 . Compounds of active metals (Zn, Na, Mg) are reducible by H whereas those of noble metals (Cu, Ag, Au) 2 are not reducible. EIt 2 . The mass of a substance deposited on the cathode or anode during electrolysis is given by w = . F 3 . Faraday's second law of electrolysis is related to the equivalent mass of the electrolyte. 4 . Equivalent conductance at infinite dilution of salt AB is equal to the sum of equivalent conductances of ions, A+ and B– at infinite dilution. 5 . The standard reaction potential of Cl–|AgCl|Ag half-cell is related to that of Ag+|Ag half-cell through the RT expression E°Ag+|Ag = E°Cl–|AgCl|Ag + F InKSP(AgCl). 6 . The cell potential is given by Ecell = ERP(cathode) – ERP(anode) 7 . In a galvanic cell, the half-cell with higher reduction potential acts as a reducing agent. 8 . In an electrode concentration cell, the cell reaction Zn(c1) Zn(c2) will be spontaneous if c1 > c2. 9 . The redox reaction involved in galvanic cell is a non-spontaneous process. FILL IN THE BLANKS 1 . A dilute solution of sulphuric acid during electrolysis liberate .................... gas at anode. 2 . Among metals .................... is the strongest reducing agents in aqueous solutions. 3 . Lead is able to displace silver from AgNO3 solution because its standard oxidation potential is .................... than that of silver. 4 . Coulomb refers to .................... of electricity while ampere refers to .................... at which it flows. 5 . During electrolysis of aqueous solution of CuSO4 using Pt electrodes the product at anode is ................... . 6 . The quantity of electricity required for complete reduction of 0.5 mole of MnO4– to Mn2+ is ................... C. 7 . eq × normality = .................... . 8 . The presence of electrolytes .................... the rate of corrosion. 9 . The more negative the standard potential, the .................... is its ability to displace hydrogen from acids. 1 0 . In the calomel half-cell, the reduction reaction to be considered is .................... . MATCH THE COLUMN Match the items of column I to those of column I : 1. Column-I Column-II (A) Cell constant (p) E0 + E0 (B) Anode cathode anode (C) Conductance (q) /A (r) Mass of product deposited by 1 coulomb of electricity. (D) Electrochemical equivalent (s) (Resistance)–1 (E) E 0 ll (u) Involve oxidation ce 2. Column-I Column-II (A) Cathode (p) Primary cell (B) 1 Coulomb (q) Secondary cell (C) Dry cell (r) 6.24 × 1018 electrones (D) Lead strong cell (s) Concentration cell (E) Zn|Zn2+(0.01M)||Zn2+(0.1M)|Zn (u) Positive terminal of electrochemical cell
3. Column-I Column-II (p) –G° (A) Electrolytic cell (q) Concentration cell (B) nFE0 (r) 96500 Coulombs Cell (s) Device converting electrical energy into (C) Ecell = 0.059 log C cathode chemical energy n C anode (u) Salt bridge (D) Diffusion of ions (E) 1 Faraday 4. Column-I Column-II (A) Conductance (p) Cm–1 (B) Specific conductance (q) Ohm–1 cm2 mol–1 (C) Cell constant (r) Ohm–1 (D) Equivalent conductance (s) Ohm–1 cm–1 (E) Molar conductance (u) Ohm–1 cm2 equivalent–1 ASSERTION & REASON These questions contains, Statement I (assertion) and Statement II (reason). (A) Statement-I is true, Statement-II is true ; Statement-II is correct explanation for Statement-I. (B) Statement-I is true, Statement-II is true ; Statement-II is NOT a correct explanation for statement-I (C) Statement-I is true, Statement-II is false (D) Statement-I is false, Statement-II is true 1 . Statement-I : In electrolysis, the quantity of electricity needed for depositing 1 mole of silver is different from that required for 1 mole of copper. Because Statement-II : The molecular weights of silver and copper are different. 2 . Statement-I : Equivalent conductance of all electrolytes decreases with increasing concentration. Because Statement-II : Lesser number of ions are available per gram equivalent at higher concentration. 3 . Statement-I : If an aqueous solution of NaCl is electrolysed, the product obtained at the cathode is H2 gas and not Na. Because Statement-II : Gases are liberated faster than the metals. 4 . Statement-I : Molar conductivity of a weak electrolyte at infinite dilution cannot be determined experimen- tally. Because Statement-II : Kohlrausch law help to find the molar conductivity of a weak electrolyte at infinite dilution. 5 . Statement-I : Gold chloride (AuCl3) solution cannot be stored in a vessel made of copper, iron, nickel, chromium, zinc or tin. Because Statement-II : Gold is very precious metal.
6 . Statement-I : In the Daniel cell, if concentration of Cu2+ and Zn2+ ions are doubled, the emf of the cell will not change. Because Statement-II : If the concentration of ions in contact with the metals is doubled, the electrode potential is doubled. 7 . Statement-I : H2 + O2 fuel cell gives a constant voltage throughout its life. Because Statement-II : In this fuel cell, H2 reacts with OH– ions, yet the overall concentration of OH– ions does not change. 8 . Statement-I : Blocks of magnesium are often stapped to steel hulls of ocean going ships. Because Statement-II : Magnesium causes cathodic protection of iron. 9 . Statement-I : Absolute value of E0red of an electrode cannot be determined. Because Statement-II : Neither oxidation nor reduction can take place alone. COMPREHENSION BASED QUESTIONS Comprehension # 1 Copper reduces NO – into NO and NO depending upon conc. of HNO in solution. Assuming 32 3 [Cu2+] = 0.1 M, and P = P = 10–3 atm and using given data answer the following questions : NO NO2 E°Cu2+/Cu = +0.34 volt ; E = +0.96 volt N O 3 / NO E = +0.79 volt ; RT N O 3 / NO2 at 298 K (2.303) = 0.06 volt F 1 . ECell for reduction of NO3– NO by Cu(s), when [HNO3] = 1 M is [At T = 298] (A) ~0.61 (B) ~0.71 (C) ~0.51 (D) ~0.81 2 . At what HNO concentration thermodynamic tendency for reduction of NO – into NO and NO by copper 3 32 is same ? (A) 101.23 M (B) 100.56 M (C) 100.66 M (D) 100.12 M Comprehension # 2 Accidentally chewing on a stray fragment of aluminium foil can causes a sharp tooth pain if the aluminium comes in contact with an amalgam filling. The filling, an alloy of silver, tin and mercury, acts as the cathode of a tiny galvanic cell, the aluminium behaves as the anode, and saliva serves as the electrolyte. When the aluminium and the filling come in contact, an electric current passage from the aluminium to the filling which is sensed by a nerve in the tooth. Aluminium is oxidized at the anode, and O2 gas is reduced to water at the cathode. E = –1.66 V, E = 1.23 V Al3 / Al O2 ,H / H2O 1 . Net reaction taking place when amalgam is in contact with aluminium foil : (A) Al + O2 + OH– Al(OH–) + H2O (B) 4Al + 3O2 + 12H+ 4Al3+ + 6H2O (C) 4Al + 3O 4Al O 2 23 (D) 2H + O 2H O 2 2 2 2 . Standard E.M.F. experienced by the person with dental filling is : (A) +2.89 V (B) –2.89 V (C) –0.93 V (D) +0.43 V
3 . The standard reduction potential of the reaction, H2O + e– 1 H2 + OH– at 298 K is : 2 RT (B) E° = RT ln PH2 1/2 [OH ] (A) E° = 2F ln K w F PH2 1 / 2 RT [H ] (D) E° = F ln K w (C) E° = RT ln F MISCELLANEOUS TYPE QUESTION ANSWER KEY EXERCISE -3 True / False 1. F 2. T 3. T 4. T 5. F 6. T 7. F 8. T 9. F Fill in the Blanks 1. O 2. Lithium 3. Higher 4. Amount, rate 2 8. Increases 6. 2.5 × 96500 C 7. × 103 5. Oxygen 10. Hg2Cl2 (s) + 2e– 2Hg () + 2Cl– (aq) 9. Greater Match the Column 1. A - (q), B - (u), C - (s), D - (r), E - (p) 2. A - (u), B - (r), C - (p), D - (q), E - (s) 3. A - (s), B - (p), C - (q), D - (u), E - (r) 4. A - (r), B - (s), C - (p), D - (u), E - (r) Assertion - Reason Questions 1. B 2. C 3. C 4. B 5. B 6. C 7. A 8. A 9. A Comprehension Based Questions Comprehension # 1: 1. (B) 2. (C) Comprehension # 2: 1. (A) 2. (C) 3. (A) 3. (D) Comprehension # 3: 1. (B) 2. (A)
EXERCISE–04 [A] CONCEPTUAL SUBJECTIVE EXERCISE 1 . The resistance of a N/10 KCl solution is 245 ohms. Calculate the specific conductance and the equivalent conductance of the solution if the electrodes in the cell are 4 cm apart and each having an area of 7.0 sq. cm. 2 . 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 the resistance of the mixture using the same cell. (Assume that there is no increase in the degree of dissociation of A and B on mixing.) 3 . In a conductivity cell the two platinum electrodes, each of area 10 sq. cm. are fixed 1.5 cm apart. The cell contained 0.05 N solution of a salt. If the two electrodes are just half dipped into the solution which has a resistance of 50 ohms, find equivalent conductance of the salt solution. 4 . A big irregular shaped vessel contained water, the sp. conductance of which was 2.56 × 10–5 mho cm–1. 500g of NaCl was then added to the water and the specific conductance after the addition of NaCl, was found to be 3.10 × 10–5 mho cm–1. Find the capacity of the vessel if it is fulfilled with water. ( N aC l = 149.9) 5 . The equivalent conductance of 0.10 N solution of MgCl is 97.1 mho cm2 eq–1. A cell with electrodes that 2 are 1.50 cm2 in surface are and 0.50 cm apart is filled with 0.1N MgCl solution. How much current will 2 flow when the potential difference between the electrodes is 5 volts? 6 . At 18°C the mobilities of NH + and ClO – ions are 6.6 × 10–4 and 5.7 × 10–4 cm2 volt–1 sec–1 at infinite dilution. 44 Calculate equivalent conductance of ammonium chlorate solution. 7 . For H+ and Na+ the values of are 349.8 and 50.11. Calculate the mobilities of these ions and their velocities if they are in a cell in which the electrodes are 5 cm apart and to which a potential of 2 volts is applied. 8 . The equivalent conductance of an infinitely dilute solution NH Cl is 150 and the ionic conductances of OH– 4 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 0.01 N solution NH OH is 9.6, what will be its degree 4 of dissociation? 9 . Calculate the dissociation constant of water at 25°C from the following data. Specific conductance of HO = 5.8 × 10–8 mho cm–1 H+ = 350.0 and = 198.0 mho cm2 2 OH– 1 0 . Calculate K of acetic acid if its 0.05 N solution has equivalent conductance of 7.36 mho cm2 at 25°C. a ( = 390.70) CH3COOH 1 1 . The sp. cond. of a saturated solution of AgCl at 25°C after substracting the sp. conductance of conductivity of water is 2.28 × 10–6 mho cm–1. Find the solubility product of AgCl at 25°C. ( = 138.3 mho cm2) AgCl 1 2 . The specific conductance of a N/10 KCl solution at 18°C is 1.12 × 10–2 mho cm–1. The resistance of the solution contained in the cell is found to be 65 ohms. Calculate the cell constant. 1 3 . When a solution of conductance 1.342 mho m–1 was placed in a conductivity cell with parallel electrodes, the resistance was found to be 170.5 ohm. The area of the electrodes is 1.86 × 10–4 sq.meter. Calculate the distance between the two electrodes in meter.
1 4 . The resistance of two electrolytes X and Y were found to be 45 and 100 respectively when equal volumes of both the solutions were taken in the same cell in two different experiments. If equal volumes of these solutions are mixed in the same cell, what will be the conductance of the mixture? 1 5 . The resistance of an aqueous solution containing 0.624 g of CuSO4. 5H2O per 100 cm3 of the solution in a conductance cell of cell constant 153.7 per meter is 520 ohms at 298 K. Calculate the molar conductivity. (CuSO . 5H O = 249.5) 42 1 6 . Given the equivalent conductance of sodium butyrate, sodium chloride and hydrogen chloride as 83, 127 and 426 mho cm2 at 25°C respectively. Calculate the equivalent conductance of butyric acid at infinite dilution. 1 7 . For 0.0128 N solution of acetic acid at 25°C, equivalent conductance of the solution is 1.4 mho cm3 eq–1 and = 391 mho cm2 eq–1. Calculate dissociation constant (K ) of acetic acid. a 1 8 . The specific conductance at 25°C of a saturated solution of SrSO is 1.482 × 10–4 ohm–1 cm–1 while that 4 of water used is 1.5 × 10–6 mho cm–1. Determine at 25°C the solubility in g per litre of SrSO in water. Molar 4 ionic conductance of Sr2+ and SO 2– ions at infinite dilution are 59.46 and 79.8 ohm–1 cm2 mole–1 respectively. 4 [Sr = 87.6, S = 32, O = 16] 1 9 . Specific conductance of pure water at 25°C is 0.58 × 10–7 mho cm–1. Calculate ionic product of water (K ) W if ionic conductances of H+ and OH– ions at infinite dilution are 350 and 198 mho cm2 respectively at 25°C. 2 0 . How long a current of 3A has to be passed through a solution of AgNO , to coat a metal surface of 3 80 cm2 with 5µm thick layer? Density of silver = 10.8 g/cm3. 2 1 . 3A current was passed through an aqueous solution of an unknown salt of Pd for 1 hr. 2.977 g of Pd+n was deposited at cathode. Find n. 2 2 . 50 mL of 0.1 M CuSO solution is electrolysed with a current of 0.965 A for a period of 200 sec. The reactions 4 at electrodes are : Cathode : Cu2+ + 2e– Cu(s) Anode : 2H O O+ 4H+ + 4e. 2 2 Assuming no change in volume during electrolysis, calculate the molar concentration of Cu2+, H+ and SO 2– 4 at the end of electrolysis. 2 3 . A metal is known to form fluoride MF . When 10 A of electricity is passed through a molten salt for 2 330 sec., 1.95 g of metal is deposited. Find the atomic weight of M. What will be the quantity electricity required to deposit the same mass of Cu form CuSO ? 4 2 4 . An electric current is passed through electrolytic cells in series one containing Ag(NO3) (aq.) and other H2SO4 (aq.) What volume of O measured at 25°C and 750 mm Hg pressure would be liberated from H SO if 2 24 (a) one mole of Ag+ is deposited from AgNO solution 3 (b) 8 × 1022 ions of Ag+ are deposited from AgNO solution. 3 2 5 . Cd amalgam is prepared by electrolysis of a solution CdCl using a mercury cathode. How long should a 2 current of 5A be passed in order to prepare 12 % Cd-Hg amalgam on a cathode of 2g, Hg (atomic weight of Cd = 112.4) 2 6 . After electrolysis of NaCl solution with inert electrodes for a certain period of time, 600 mL of the solution was left. Which was found to be 1N in NaOH. During the same time, 31.75 g of Cu deposited in the copper voltameter in series with the electrolytic cell. Calculate the percentage yield of NaOH obtained. 27 . During the discharge of a lead storage battery, the density of sulphuric acid fell from 1.294 to 1.139 g.mL–1. H SO of density 1.294 gmL–1 is 39% and that of density 1.139 g.mL–1 is 20% by weight. 24
The battery holds 3.5 L of acid and the volume practically remains constant during discharge. Calculate the number of ampere hours for which the battery must have been used. The discharging and charging reactions are. Pb + SO 2– PbSO + 2e– (charging) 4 4 PbO + 4H+ + SO 2– + 2e– PbSO + 2H O (discharging) 2 4 4 2 2 8 . The e.m.f. of the cell obtained by combining Zn and Cu electrode of a Daniel cell with N calomel electrode in two different arrangements are 1.083 V and 0.018 V respectively at 25°C. If the standard reduction potential of N calomel electrode is 0.28 V find the emf of Daniel cell. 2 9 . Same quantity of electricity is being used to liberate iodine (at anode) and a metal x (at cathode). The mass of x liberated is 0.617 g and the iodine liberated is completely reduced by 46.3 cc of 0.124 M sodium thiosulphate. Find the equivalent mass of metal x. 3 0 . 100 mL CuSO (aq) was electrolyzed using inert electrodes by passing 0.965 A till the pH of the resulting 4 solution was 1. The solution after electrolysis was neutralized, treated with excess KI and titrated with 0.04 M Na2S2O3. Volume of Na2S2O3 required was 35 mL. Assuming no volume change during electrolysis, calculate : (a) duration of electrolysis if current efficiency is 80 % (b) initial concentration (M) of CuSO . 4 3 1 . A current of 3.7 A is passed for 6 hrs between Pt electrodes in 0.5 L of 2M solution of Ni(NO ) . What 32 will be the molarity of solution at the end of electrolysis ? 3 2 . Calculate the EMF of a Daniel cell when the concentration of ZnSO and CuSO are 0.001 M and 44 0.1 M respectively. The standard potential of the cell is 1.1 V. 3 3 . EMF of the cell Zn|ZnSO (a = 0.2)||ZnSO (a )|Zn is –0.0088 V at 25°C. Calculate the value of a . 4 42 2 3 4 . The EMF of the cell M|Mn+ (0.02 M)||H+ (1 M)|H (g) (1 atm), Pt at 25°C is 0.81 V. Calculate the valency 2 of the metal if the standard oxidation potential of the metal is 0.76 V. 3 5 . Equinormal solution of two weak acids, HA (pKa = 3) and HB (pKa = 5) are each placed in contact with standard hydrogen electrode at 25°C. When a cell is constructed by interconnecting them through a salt bridge find the e.m.f. of the cell. 3 6 . In two vessels each containing 500 mL water, 0.5 m mol of aniline (K = 10–9) and 25 m mol of HCl are b added separately. Two hydrogen electrodes are constructed using these solutions. Calculate the emf of cell made by connecting them appropriately. 3 7 . The emf of the cell Ag|AgI|KI (0.05 M)||AgNO (0.05 M)|Ag is 0.788 V. Calculate the solubility product of AgI. 3 3 8 . The cell Pt, H (1 atm)|H+ (pH = x)|| Normal calomel Electrode has an EMF of 0.67 V at 25°C. 2 Calculate the pH of the solution. The oxidation potential of the calomel electrode on hydrogen scale is –0.28 V. 3 9 . Estimate the cell potential of a Daniel cell having 1.0 M Zn++ and originally having 1.0 M Cu++ after sufficient NH3 has been added to the cathode compartment to make NH3 concentration 2.0 M. Given Kf for [Cu(NH ) ]2+ = 1 × 1012, E° for the reaction, Zn + Cu2+ Zn2+ + Cu is 1.1 V. 34 4 0 . Consider the cell Ag|AgBr(s)|Br–||AgCl(s)|Cl–|Ag at 25°C. The solubility product constants of AgBr & AgCl are respectively 5 × 10–13 & 1 × 10–10. For what ratio of the concentration of Br– & Cl– ions would the em.f. of the cell be zero? 4 1 . The pK of AgI is 16.07. If the E° value for Ag+/Ag is 0.7991 V, find the E° for the half cell reaction sp AgI (s) + e– Ag + I–
4 2 . Voltage of the cell Pt, H (1 atm)|HOCN (1.3 × 10–3 M)||Ag+(0.8 M)|Ag(s) is 0.982 V. Calculate the K 2a for HOCN. Neglect [H+] because of oxidation of H (g). 2 Ag+ + e– Ag (s) = 0.8 V 4 3 . The standard oxidation potential of Zn referred to SHE is 0.76 V and that of Cu is –0.34 V at 25°C. When excess of Zn is added to CuSO , Zn displaces Cu2+ till equilibrium is reached. What is the ratio of Zn2+ to 4 Cu2+ ions at equilibrium? 4 4 . The standard reduction potential values, E° (Bi3+ /Bi) and E° (Cu2+ / Cu) are 0.226 V and 0.344 V respectively. A mixture of salts of bismuth and copper at unit concentration each is electrolysed at 25°C. To what value can [Cu2+] be brought down before bismuth starts to deposit, in electrolysis. 4 5 . Calculate the potential of an indicator electrode versus the standard hydrogen electrode, which originally contained 0.1 M MnO – and 0.8 M H+ and which was treated with Fe2+ necessary to reduce 90% of the MnO – 44 to Mn2+. MnO – + 8H+ + 5e Mn2+ + H O, E° = 1.51 V, 4 2 4 6 . K for dissociation of [Ag(NH ) ]+ into Ag+ and NH is 6 × 10–8. Calculate E° for the following half reaction; d 32 3 Ag (NH ) + + e– Ag + 2NH 32 3 Given Ag+ + e– Ag, E° = 0.799 V 4 7 . The overall formation constant for the reaction of 6 mole of CN– with cobalt (II) is 1 × 1019. The standard reduction potential for the reaction [Co(CN) ]3– + e– Co(CN) 4– is –0.83 V. Calculate the formation constant 6 6 of [Co(CN) ]3–. 6 Given Co3+ + e– Co2+ ; E° = 1.82 V 4 8 . Calculate the e.m.f. of the cell Pt|H |(1.0 atm)|CH COOH (0.1 M)||NH (aq, 0.01 M)|H (1.0 atm)|Pt 23 32 K (CH COOH) = 1.8 × 10–5, K , (NH ) = 1.8 × 10–5. a3 b3 49 . An external current source giving a current of 5.0 A was joined with Daniel cell arrangement opposing the normal current flow and was removed after 10 hrs. Before passing the current the LHE and RHE contained 1L each of 1M Zn2+ and Cu2+ respectively. Find the EMF supplied by the Daniel cell after removal of the external current source. E° of Zn2+/Zn and Cu2+/Cu at 25°C is –0.76 and +0.34 V respectively. 5 0 . Calculate the equilibrium constant for the reaction : 3Sn (s) + 2Cr O 2– + 28 H+ 3 Sn+4 + 4Cr3+ + 14H O 27 2 E° for Sn/Sn2+ = 0.136 V E° for Sn2+/Sn4+ = –0.154 V E° for Cr O 2–/Cr3+ = 1.33 V 27 5 1 . Calculate the voltage E, of the cell at 25°C Mn(s)|Mn(OH )(s)|Mn2+(x M), OH– (1.00 × 10–4 M)||Cu2+ (0.675 M)|Cu(s) 2 given that K = 1.9 × 10–13 for Mn(OH) (s) E° (Mn2+/Mn) = –1.18 V, E°(Cu+2/Cu) = +0.34 V sp 2 5 2 . Calculate the voltage E, of the cell Ag(s) AgIO (s)|Ag+ (x M), HIO (0.300 M)||Zn2+ (0.175 M)|Zn (s) 33
if K = 3.02 × 10–8 for AgIO (s) and K = 0.162 for HIO , E°(Zn+2/Zn) = –0.76 V, E° (Ag/Ag+) = –0.8 V) SP 3a 3 5 3 . The voltage of the cell Pb(s)|PbSO (s)|NaHSO (0.600 M)||Pb2+(2.50 × 10–5 M)|Pb (s) 44 is E = +0.061 V. Calculates K = [H+] [SO 2–]/[HSO –], the dissociation constant for HSO –. 2 44 4 Given Pb(s) + SO 2– PbSO + 2e– (E° = 0.356 V), E° (Pb2+ / Pb) = –0.126 V. 4 4 5 4 . The voltage of the cell Zn(s)|Zn(CN) 2– (0.450 M), CN– (2.65 × 10–3 M)||Zn2+(3.84 × 10–4 M)|Zn(s) is E = +0.099 V. 4 Calculate the constant Kf for Zn2+ + 4CN– Zn(CN)42–, the only Zn2+ + CN– complex reaction of importance. CONCEPTUAL SUBJECTIVE EXERCISE ANSWER KEY EXERCISE-4(A) 1 . 2.332 × 10–3mho cm–1, 23.32 mho cm2eq–1 2 . R = 66.67 ohms 3. 120 mho cm2 eq–1 4 . V = 2.34 × 108 cc 5 . 0.1456 amp 6. 118.67 mho cm2 eq–1 7 . µ°H+ = 3.62 × 10–3 cm2 volt–1 sec–1, µ° = 5.20 × 10–4 cm2 volt–1 sec–1 Na velocity of H+ = 1.45 × 10–3 cm sec–1 , velocity of Na+ = 2.08 × 10–4 cm sec–1 8 . 272, 0.0353 9 . 1.8×10–16mole/litre 10. 1.76×10–5 mole/litre 1 1 . 2.70×10–10(mole/litre)2 1 2 . 0.728 cm–1 13. 4.25×10–2metres 1 4 . 0.016 mho 1 5 . 118.2 mho cm2mol–1 16. 382 mho cm2 eq–1 1 7 . 1.6 × 10–7 1 8 . 0.1934 g/L 19. 1 × 10–14 (mole/litre)2 2 0 . t = 128.66 sec 21. n = 4 26. = 60% 22. Cu2+ = 0.08M, H+ = 0.04M, SO 2– = 0.1M 23 . A=114, Q=5926.8C 29. Eq.wt = 107.468 2 5 . t = 93.65 sec 4 2 8 . E = 1.1 V 2 4 . (a) V(O )=6.2 L, (b) V(O )=0.824L 22 2 7 . 265 Amp. hr. 30. 1250 S, 0.064 M 3 1 . 1.172 M 32. E = 1.159 V 3 3 . a = 0.1006 M 34. n = 2 35. E = 0.059 V 2 3 7 . K = 1.16 × 10–16 38. pH = 6.61 3 6 . E = 0.395 V SP 41. E° = –0.149 V 3 9 . E° = 0.71 V 4 2 . Ka = 6.74 × 10–4 4 0 . [Br–] : [Cl–] = 1 : 200 4 5 . 1.39 V 4 8 . –0.46 V 4 3 . [Zn2+]/[Cu2+]=1.941×1037 44. [Cu2+] = 10–4 M 5 1 . 1.66 V 5 4 . 5.4 × 1016 4 6 . 0.373 V 47. K = 8.28 × 1063 4 9 . 1.143 V f 50. K = 10268 5 2 . –1.188 V 53. 1.06 × 10–2
EXERCISE–04 [B] BRAIN STORMING SUBJECTIVE EXERCISE 1 . The e.m.f. of cell : H2(g)|Buffer||Normal calomal electrode is 0.6885 V at 40°C when the barometric pressure is 725 mm of Hg. What is the pH of the solution. E°calomal = 0.28. 2 . A direct current of 1.25 A was passed through 200 mL of 0.25 M Fe2(SO4)3 solution for a period of 1.1 hour. The resulting solution in cathode chamber was analyzed by titrating against acidic KMnO4 solution. 25 mL permaganate solution was required to reach the end point. Determine molarity of KMnO4 solution. 3 . An electrochemical cell is constructed with an open switch as shown below : V Sn X Salt Bridge 0.5 M Sn2+ 0.1 M Xn+ When the switch is closed, mass of tin-electrode increases. If E° (Sn2+ / Sn) = –0.14 V and for E° (Xn+ / X) = – 0.78 V and initial emf of the cell is 0.65 V, determine n and indicate the direction of electron flow in the external circuit. 4 . 10 g fairly concentrated solution of CuSO is electrolyzed using 0.01 F of electricity. Calculate : 4 (a) The weight of resulting solution (b) Equivalents of acid or alkali in the solution. 5 . One of the methods of preparation of per disulphuric acid, H2S2O8, involve electrolytic oxidation of H2SO4 at anode (2H2SO4 H2S2O8 + 2H+ + 2e–) with oxygen and hydrogen as by - products. In such an electrolysis, 9.722 L of H2 and 2.35 L of O2 were generated at STP. W hat is the weight of H2S2O8 formed? 6 . Assume that impure copper contains only iron, silver and a gold as impurities. After passage of 140 A, for 482.5 sec, of the mass of the anode decreased by 22.260 g and the cathode increased in mass by 22.011 g. Estimate the % iron and % copper originally present. 7 . For the galvanic cell : Ag|AgCl(s)|KCl(0.2 M)||KBr(0.001 M)|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 25°C. [K = 2.8 × 10–10 ; K = 3.3 × 10–13] sp(AgCl) sp(AgBr) 8 . An aqueous solution of NaCl on electrolysis gives H2(g), Cl2(g) and NaOH according to the reaction : 2Cl–(aq) + 2H2O 2 OH – + H2(g) + Cl2(g) (aq) A direct current of 25 amperes with a current efficiency of 62% is passed through 20 liters 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).
9 . An acidic solution of Cu2+ salt containing 0.4 of Cu2+ is electrolyzed until all the copper is deposited. The electrolysis is continued for seven more minutes with the volume of solution kept at 100 mL and the current at 1.2 amp. Calculate the volume of gases evolved at NTP during the entire electrolysis. 1 0 . In the refining of silver by electrolytic method what will be the weight of 100 g Ag anode if 5 ampere current is passed for 2 hours? Purity of silver is 95% by weight. 1 1 . Hydrogen peroxide can be prepared by successive reactions : 2NH HSO H + (NH ) S O 44 2 42 2 8 (NH4)2S2O8 + 2H2O 2NH4HSO4 + H2O2 The first reaction is an electrolytic reaction the second is steam distillation. What amount of current would have to be used in first reaction to produce enough intermediate to yield 100 g pure H O per hour? Assume 22 50% anode current efficiency. 1 2 . Dal lake has water 8.2 × 1012 litre approximately. A power reactor produces electricity at the rate of 1.5 × 106 coulomb per second at an appropriate voltage. How many years would it take to electrolyse the lake? 1 3 . Determine the degree of hydrolysis and hydrolysis constant of aniline hydrochloride in M/32 solution of salt at 298 K from the following cell data at 298 K. Pt|H2(1 atm)|H+(1 M)|| M/32 C6H5NH3Cl|H2(1 atm)|Pt ; Ecell = –0.188 V. 1 4 . The emf of the cell, Pt|H (1 atm)|H+(0.1 M, 30 mL)|| Ag+ (0.8 M) Ag is 0.9 V. Calculate the emf when 2 40 mL of 0.05 M NaOH is added. 1 5 . A dilute aqueous solution of KCl was placed between two electrodes 10 cm apart, across which a potential of 6 volt was applied. How far would the K+ ion move in 2 hours at 25°C? Ionic conductance of K+ ion at infinite dilution at 25°C is 73.52 ohm–1 cm2 mole–1? 1 6 . 100 mL CuSO (aq) was electrolyzed using inert electrodes by passing 0.965 A till the pH of the resulting solution 4 was 1. The solution after electrolysis was neutralized, treated with excess KI and titrated with 0.04 M Na S O . Volume of Na S O required was 35 mL. Assuming no volume change during electrolysis, 22 3 22 3 calculate : (a) duration of electrolysis if current efficiency is 80% (b) initial concentration (M) of CuSO4 1 7 . Calculate the equilibrium concentration of all ions in an ideal solution prepared by mixing 25.00 mL of 0.100 M Tl+ with 25.00 mL of 0.200 M Co3+. E° (Tl+/Tl3+) = – 1.25 V, E° (Co3+/Co2+) = 1.84 V 1 8 . Determine at 298 for cell : Pt|Q, QH2 , H+||1M KCl|Hg2Cl2|Hg(l)|Pt (a) it's emf when pH = 5.0 (b) the pH when Ecell = 0 (c) the positive electrode when pH = 7.5 given E°RP(RHS) = 0.28, E°RP(LHS) = 0.699
1 9 . At 25°C, Hf(H2O, l) = –56700 J/mol and energy of ionization of H2O(l) = 19050 J/mol. What will be the reversible EMF at 25°C of the cell, Pt|H2(g)(1 atm)|H+|| OH–|O2 (g)(1 atm)|Pt, if at 26°C the emf increase by 0.001158 V. 2 0 . Calculate the cell potential of a cell having reaction Ag2S + 2e– 2 Ag + S2– in a solution buffered at pH = 3 and which is also saturated with 0.1 M H2S. For H2S : K1 = 10–8 and K2 = 1.1 × 10–13, Ksp(Ag2S) = 2 × 10–49, E°Ag+/Ag = 0.8. 2 1 . Calculate the solubility and solubility product of Co2[Fe(CN)6] in water at 25°C from the following data : Conductivity of a saturated solution of Co2[Fe(CN)6] is 2.06 × 10–6–1cm–1 and that of water used 4.1 × 10–7 –1cm–1. The ionic molar conductivities of Co2+ and Fe(CN)64– are 86.0 –1cm2mol–1 and 444.0 –1cm–1mol–1. 2 2 . A sample of water from a large swimming pool has a resistance of 9200 at 25°C when placed in a certain conductance cell. When filled with 0.02 M KCl solution, the cell has a resistance of 85 at 25°C. 500 g of NaCl were dissolved in the pool, which was throughly stirred. A sample of this solution gave a resistance of 7600 . Calculate the volume of water in the pool. Given : Molar conductance of NaCl at that concentrations is 126.5 –1cm2mol–1 and molar conductivity of KCl at 0.02 M is 138 –1cm2 mol–1. BRAIN STORMING SUBJECTIVE EXERCISE ANSWER KEY EXERCISE-4(B) 1. 6.6 2 . 0.41 M 3 . n = 3 & X-electrode to Sn-electrode 4 . final weight = 9.6 g, 0.01 eq. of acid 5 . 43.45 g 6 . Cu = 98.88%, Fe = 0.85% 7 . – 0.037 V 8 . 48.71 hour, [OH–] = 1.41 M 9 . V(O2) = 99.68 mL, V(H2) = 58.46 mL, Total vol. = 158.1 mL 1 0 . 57.5894 g 1 1 . 315.36 A 1 2 . 1.9 million year 1 3 . h = 2.12 × 10–2, Kh = 1.43 × 10–5 M 1 4 . 0.95 V 1 5 . 3.29 cm 1 6 . 1250 s, 0.064 M 1 7 . Tl+ = 10–8 , Co+3 = 2 × 10–8 1 8 . (a) –0.124V (b) 7.1 (c) calomel electrode 1 9 . 0.4414 V 2 0 . –0.167 V 2 1 . Ksp = 7.682 × 10–17 2 2 . 2 × 105 dm3
EXERCISE - 05 [A] JEE-[MAINS] : PREVIOUS YEAR QUESTIONS 1 . For a cell reaction involving a two-electron change, the standard e.m.f. of the cell is found to be 0.295V at 25° C. The equilibrium constant of the reaction at 25°C will be : [AIEEE-2003] (A) 10 (B) 1 × 1010 (C) 1 × 10–10 (D) 29.5 × 10–2 2 . Standard reduction electrode potentials of three metals A, B and C are re spect ively + 0.5V, – 3.0V and –1.2 V. The reducing powers of these metals are : [AIEEE-2003] (A) C > B > A (B) A > C > B (C) B > C > A (D) A > B > C 3 . For the redox reaction : Zn(s) + Cu2+ (0.1M) Zn2+ (1M) + Cu(s) taking place in a cell, E° is 1.10 volt. E for the cell will be 2 .30 3 RT 0.0591 [AIEEE-2003] Cell Cell F (D) 1.80 volt (A) 1.07 volt (B) 0.82 volt (C) 2.14 volt 4 . When during electrolysis of a solution of AgNO 9650 coulombs of charge pass through the electroplating 3 bath, the mass of silver deposited on the cathode will be : [AIEEE-2003] (A) 21.6g (B) 108g (C) 1.08g (D) 10.8g 5 . Consider the following E0 values [AIEEE-2004] E0 Fe2 = + 0.77V E0 = – 0.14V (D) 0.63V Fe3 Sn2 Sn Under standard conditions the potential for the reaction Sn(s) + 2Fe3+ (aq) 2Fe2+(aq) + Sn2+(aq) is (A) 0.91V (B) 1.40V (C) 1.68V 6 . The standard e.m.f. of a cell, involving one electron change is found to be 0.591 V at 25°C. The equilibrium constant of the reaction is (F = 96,500C mol–1 ; R = 8.314 JK–1 mol–1) [AIEEE-2004] (A) 1.0 × 1010 (B) 1.0 × 105 (C) 1.0 × 101 (D) 1.0 × 1030 7 . The limiting molar conductivities for NaCl, KBr and KCl are 126,152 and 150Scm2 mol–1 respectively. The for NaBr is : [AIEEE-2004] (A) 278 S cm2 mol–1 (B) 176 S cm2 mol–1 (C) 128 S cm2 mol–1 (D) 302 S cm2 mol–1 8 . In a cell that utilises the reaction Zn(s) + 2H+(aq.) Zn2+(aq) + H (g) addition of H SO to cathode compartment, will [AIEEE-2004] 2 24 (A) increase the E and shift equilibrium to the right (B) lower the E and shift equilibrium to the right (C) lower the E and shift equilibrium to the left (D) increase the E and shift equilibrium to the left 9. The E0 values for Cr, Mn, Fe and Co are –0.41, + 1.57, +0.77 and + 1.97V respectively. For which M3 M2 one of these metals the change in oxidation state from +2 to +3 is easiest ? [AIEEE-2004] (A) Fe (B) Mn (C) Cr (D) Co
10. For a spontaneous reaction the G, equilibrium constant (K) and E 0 will be respectively [AIEEE-2005] Cell (A) –ve, < 1, –ve (B) –ve, >1, –ve (C) –ve, >1, +ve (D) +ve, >1, –ve 1 1 . Aluminium oxide may be electrolysed at 1000°C to furnish aluminium metal (At. Mass = 27 amu; 1 Faraday = 96500 Coulombs).The cathode reaction is [AIEEE-2005] A3+ + 3e– A0 To prepare 5.12 kg of aluminium metal by this method would require. (A) 5.49 × 104 C of electric charge (B) 5.49 × 101 C of electric charge (C) 5.49 × 107 C of electric charge (D) 1.83 × 107 C of electric charge 1 2 . The highest electrical conducitivity of the following aqueous solution is of [AIEEE-2005] (A) 0.1 M fluoroacetic acid (B) 0.1 M difluoroacetic acid (C) 0.1 M acetic acid (D) 0.1 M chloroacetic acid 1 3 . Electrolyte (S cm2 mol–1) KCl 149.9 KNO 145.0 3 426.2 HCl NaOAC 91.0 NaCl 126.5 Calculate using appropriate molar conductances of the electrolytes listed above at infinite dilution in HOAc H O at 25°C [AIEEE-2005] 2 (B) 217.5 (C) 517.2 (D) 552.7 (A) 390.7 1 4 . Given the data at 25°C, Ag + I– AgI + e–, E° = 0.152V Ag Ag+ + e–, E° = – 0.800 V What is the value of log Ksp for AgI ? 2 .3 0 3 RT 0.059 V [AIEEE 2006] F (A) –8.12 (B) +8.612 (C) –37.83 (D) –16.13 1 5 . Resistance of a conductivity cell filled with a solution of an electrolyte of concentration 0.1M is 100 The conductivity of this solution is 1.29 Sm–1. Resistance of the same cell when filled with 0.02M of the same solution is 520. The molar conductivity of 0.02M solution of the electrolyte will be. [AIEEE-2006] (A) 124 × 10—4 Sm2 mol–1 (B) 1240 × 10–4 Sm2 mol–1 (C) 1.24 × 104 Sm2 mol–1 (D) 12.4 × 10–4 Sm2 mol–1 16. The molar conductivities 0N aO A c and 0 C l at infinite dilution in water at 25°C are 91.0 and H 426.2 S cm2/mol respectively. To calculate 0HOAc the additional value required is : [AIEEE-2006] (A) KCl (B) NaOH (C) NaCl (D) H2O 17. Given E0 = – 0.72 V, E0 = – 0.42 V. The potential for the cell [AIEEE-2008] Cr3 / Cr Fe2 / Fe Cr | Cr3+ (0.1 M) || Fe2+ (0.01 M)|Fe is (A) 0.26 V (B) 0.339 V (C) – 0.339 V (D) –0.26 V
18. Given : [AIEEE-2009] E0 –0.036 V, E0 –0 .4 3 9 V, Fe3 / Fe Fe2 / Fe Thevalue of standard electrode potential for the change, F e 3 e Fe2 (aq ) will be :- aq (A) 0.770 V (B) –0.270 V (C) –0.072 V (D) 0.385 V 1 9 . The Gibbs energy for the decomposition of Al2O3 at 500 °C is as follows : [AIEEE-2010] 24 3 Al2O3 3 Al + O2, rG = +966 KJ mol–1 The potential difference needed for electrolytic reduction of Al2O3 at 500 °C is at least :- (A) 5.0 V (B) 4.5 V (C) 3.0 V (D) 2.5 V 20. The correct order of E values with negative sign for the four successive elements Cr, Mn, Fe and Co M2 / M is :- [AIEEE-2010] (A) Cr > Mn > Fe > Co (C) Cr > Fe > Mn > Co (B) Mn > Cr > Fe > Co (D) Fe > Mn > Cr > Co 2 1 . The reduction potential of hydrogen half-cell will be negative if :- [AIEEE-2011] (A) p(H2) = 2 atm [H+] = 1.0 M (B) p(H2) = 2 atm and [H+] = 2.0 M (C) p(H2) = 1 atm and [H+] = 2.0 M (D) p(H2) = 1 atm and [H+] = 1.0 M 2 2 . Resistance of 0.2 M solution of an electrolyte is 50 . The specific conductance of the solution is 1.3 S m–1. If resistance of the 0.4M solution of the same electrolyte is 260 , its molar conductivity is :- [AIEEE-2011] (A) 6250 S m2 mol–1 (B) 6.25 × 10–4 S m2 mol–1 (C) 625 × 10–4 S m2 mol–1 (D) 62.5 S m2 mol–1 2 3 . The standard reduction potentials for Zn2+ / Zn, Ni2+ / Ni and Fe2+ / Fe are – 0.76, – 0.23 and – 0.44 V respectively. The reaction X + Y+2 X2+ + Y will be spontaneous when [AIEEE-2012] (A) X = Zn, Y = Ni (B) X = Ni, Y = Fe (C) X = Ni, Y = Zn (D) X = Fe, Y = Zn JEE-[MAIN] : PREVIOUS YEAR QUESTIONS ANSWER KEY EXERCISE -5[A] Que. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Ans B C A D A A C A C CCBADA Que. 16 17 18 19 20 21 22 23 Ans C A A D B A B A
EXERCISE - 05 [B] JEE-[ADVANCED] : PREVIOUS YEAR QUESTIONS 1 . The standard reduction potentials of Cu2+ / Cu and Cu2+ / Cu+ are 0.337 and 0.153 V respectively. The standard electrode potential of Cu+ / Cu half cell is :- [JEE 1997] (A) 0.184 V (B) 0.827 V (C) 0.521 V (D) 0.490 V 2 . A standard hydrogen electrode has zero electrode potential because :- [JEE 1997] (A) hydrogen is easier to oxidise (B) this electrode potential is assumed to be zero (C) hydrogen atom has only one electron (D) hydrogen is the lowest element 3 . The standard reduction potential values of the three metallic cations X, Y, Z are 0.52, –3.03, and –1.18V respectively. The order of reducing power of the corresponding metals is :- [JEE 1998] (A) Y > Z > X (B) X > Y > Z (C) Z > Y > X (D) Z > X > Y 4 . A gas X at 1 atm is bubbled through a solution containing a mixture of 1M Y and 1M Z at 25°C. If the reduction potential of Z > Y > X, then :- [JEE 1999] (A) Y will oxidise X and not Z (B) Y will oxidise Z and not X (C) Y will oxidise both X and Z (D) Y will reduce both X and Z 5 . For the electrochemical cell, M|M+||X–|X,E° (M+/M) = 0.44 V and E° (X/X–) = 0.33 V. From this data, one can deduce that :- [JEE 2000] (A) M + X M+ + X– is the spontaneous reaction (B) M+ + X– M + X is the spontaneous reaction (C) Ecell = 0.77 V (D) Ecell = –0.77 V 6 . The reaction, 3 ClO– (aq) ClO – (aq) + 2 Cl– (aq) 3 is an example of :- [JEE 2001] (A) Oxidation reaction (B) Reduction reaction (C) Disproportionation reaction (D) Decomposition reaction 7 . The correct order of equivalent conductance at infinite dilution of LiCl, NaCl and KCl is:-[JEE 2001] (A) LiCl > NaCl > KCl (B) KCl > NaCl > LiCl (C) NaCl > KCl > LiCl (D) LiCl > KCl > NaCl 8 . Saturated solution of KNO is used to make salt bridge because :- [JEE 2001] 3 (A) velocity of K+ is greater than that of NO–3 (B) velocity of NO3– is greater than that of K+ (C) velocities of both K+ and NO–3 are nearly the same (D) KNO3 is highly soluble in water 9 . 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 :- [JEE 2002] MnO – (aq) + 8H+ (aq) + 5e– Mn2+ (aq) + 4H O (l) ; E° = 1.51 V 4 2 CrO – (aq) + 14H+ (aq) + 6e– 2Cr3+ (aq) + 7H O (l) ; E° = 1.38 V 7 2 Fe3+ (aq) + e– Fe2+ (aq) ; E° = 0.77 V Cl (g) + 2e– 2Cl– (aq) ; E° = 1.40 V 2 Identify the only incorrect statement regarding quantitative estimation of aqueous Fe(NO3)2. (A) MnO4– can be used in aqueous HCl (B) Cr2O72– can be used in aqueous HCl (C) MnO4– can be used in aqueous H2SO4 (D) Cr2O72– can be used in aqueous H2SO4
1 0 . In the electrolytic cell, flow of electrons is from :- [JEE 2003] (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 1 1 . Zn|Zn2+(a = 0.1 M)||Fe2+ (a = 0.01 M)|Fe. The emf of the above cell is 0.2905 V. Equilibrium constant for the cell reaction is :- [JEE 2004] (A) 100.32/0.591 (B) 100.32/0.0295 (C) 100.26/0.0295 (D) e0.32/0.295 1 2 . The half cell reactions for rusting of iron are : [JEE 2000] 2H+ + 1 + 2e– H2O ; E° = + 1.23 V, Fe2+ + 2e– Fe ; E° = – 0.44 V 2 O2 G° (in kJ) for the reaction is : (A) –76 (B) –322 (C) –122 (D) –176 Question No. 13 to 15 (3 question) Tollen's reagent is used for the detection of aldehyde when a solution of AgNO is added to glucose with 3 NH OH then gluconic acid is formed. 4 Ag+ + e– Ag ; E° = 0.8 V red CH O + HO CH O (Gluconic acid) + 2H+ + 2e– ; E° = –0.05 V 6 12 6 2 6 12 7 red Ag(NH ) + + e– Ag(s) + 2NH ; E° = – 0.337 V 32 3 [Use 2.303 × RT F = 38.92 at 298 K] [JEE 2006] = 0.0592 and F RT 13. 2Ag+ + CH O + HO 2Ag(s) + CH O + 2H+ 6 12 6 2 6 12 7 Find n K of this reaction (A) 66.13 (B) 58.38 (C) 28.30 (D) 46.29 1 4 . 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) Eoxd will increase by a factor of 0.65 from E°oxd (B) Eoxd will decrease by a factor of 0.65 from E°oxd (C) Ered will increase by a factor of 0.65 from E°red (D) Ered will decrease by a factor of 0.65 from E°red 1 5 . Ammonia is always is added in this reaction. Which of the following must be incorrect? (A) NH3 combines with Ag+ to form a complex (B) Ag(NH3)2+ is a weaker oxidising reagent than Ag+ (C) In absence of NH3 silver salt of gluconic acid is formed (D) NH3 has affected the standard reduction potential of glucose / gluconic acid electrode 1 6 . Electrolysis of a solution of MnSO in aqueous sulphuric acid is a method for the preparation of MnO as 42 per the reaction, Mn2+ + 2H O MnO (s) + 2H+ + H (g) aq 2 2 aq 2 Passing a current of 27 A for 24 hours gives one kg of MnO . What is the value of current efficiency? 2 Write the reaction taking place at the cathode and at the anode. [JEE 1997]
1 7 . 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 is the area of the tray if the thickness of the silver plating is 0.00254 cm? Density of silver is 10.5 g/cm3 :- [JEE 1997] 1 8 . Calculate the equilibrium constant for the reaction Fe2+ + Ce4+ Fe3+ + Ce3+, [given : E 0 / Ce3 1.44 V ; E 0 / F e 2 0.68 V] [JEE 1997] Ce4 Fe3 19. Calculate the equilibrium constant for the reaction, 2Fe3+ + 3I – 2Fe2+ + I –. The standard reduction potentials 3 in acidic condition are 0.77 and 0.54 V respectively for Fe3+/Fe2+ and I –/I– couples :- [JEE 1998] 3 2 0 . Find the solubility product of a saturated solution of Ag CrO in water at 298 K if the emf of the cell 24 Ag|Ag+ (satd. Ag CrO soln) ||Ag+ (0.1 M) | Ag is 0.164 V at 298 K :- [JEE 1998] 24 2 1 . 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 minute it was found that after electrolysis, the concentration of the solution was reduced to 50% of its original value. Calculate the concentration of copper sulphate in the solution to begin with. [JEE 2000] 2 2 . The following electrochemical cell has been set up :- [JEE 2000] Pt |Fe3+, Fe2+ (a = 1)||Ce4+, Ce3+ (a = 1)|Pt (I) (II) E°Fe3+/Fe2+ = 0.77 V and E°Ce4+/Ce3+ = 1.61 V 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? 2 3 . The standard potential of the following cell is 0.23 V at 15°C C & 0.21 V at 35°C. Pt|H (g)|HCl (aq)|AgCl (s)|Ag(s) 2 (i) Write the cell reaction. (ii) Calculate H0, S0 for the cell reaction by assuming that these quantities remain unchanged in the range 15°C to 35°C. (iii) Calculate the solubility of AgCl in water at 25°C. Given standard reduction potential of the Ag+/Ag couples is 0.80 V at 25°C. [JEE 2001] 2 4 . Two students use same stock solution of ZnSO4 and a solution of CuSO4. The e.m.f of one cell is 0.03 V higher than the other. The conc. of CuSO in the cell with higher e.m.f value is 0.5 M. Find out the 4 conc. of CuSO in the other cell 2.303RT 0.06 :- [JEE 2003] 4 F 2 5 . Find the equilibrium constant at 298 K for the reaction, Cu2+(aq) + In2+(aq) Cu+(aq) + In3+(aq) c Given that : E = 0.15 V, E = –0.42 V, E = –0.40 V [JEE 2000] C u 2 |C u In3|In In 2 | In 26. (a) Calculate G 0 of the following reaction f Ag+(aq) + Cl– (aq) AgCl (s) Given : G0f (AgCl) = – 109 kJ/mole, G0f (Cl–) = – 129 kJ/mole, G0f (Ag+) = 77 kJ/mole Represent the above reaction in form of a cell Calculate E0 of the cell. Find log K of AgCl 10 SP
(b) 6.593 × 10–2 g of metallic Zn (amu = 65.39) was added to 100 mL of saturated solution of AgCl. Calculate log Zn2 , given that 10 Ag 2 Ag+ + e– Ag E0 = 0.80 V Zn2+ + 2e– Zn E0 = –0.76 V Also find how many moles of Ag will be formed ? [JEE 2005] 2 7 . We have taken a saturated solution of AgBr,K of AgBr is 12 × 10–14. If 10–7 mole of AgNO are added to sp 3 1 litre of this solution find conductivity (specific conductance) of this solution in terms of 10–7 S m–1 mol–1. Given : 0 = 6 × 10–3 S m2 mol–1 ; 0 = 8 × 10–3 S m2 mol–1 ; 0( NO ) 7 × 10–3 S m2 mol–1 :-[JEE 2006] (Ag+) (Br–) 3 Question No. 28 to 30 (3 questions) Tollen’s 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 0 = 0.8 V red C6H12O6 + H2O C6H12O7 (Gluconic acid) + 2H+ + 2e– ; E 0 = – 0.05 V red Ag( NH 3 ) + e– Ag(s) + 2NH3 ; E0 = – 0.337 V 2 RT F [JEE 2006] [Use 2.303 × F = 0.0592 and RT = 38.92 at 298 K] (D) 46.29 2 8 . 2Ag+ + C6H12O6 + H2O 2Ag(s) + C6H12O7 + 2H+ Find ln K of this reaction (A) 66.13 (B) 58.38 (C) 28.30 2 9 . 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) Eoxd will increase by a factor of 0.65 from Eo0xd (B) Eoxd will decrease by a factor of 0.65 from E0oxd (C) Ered will increase by a factor of 0.65 from E 0 red (D) Ered will decrease by a factor of 0.65 from E 0 red 3 0 . Ammonia is always is added in this reaction. Which of the following must be incorrect? (A) NH3 combines with Ag+ to form a complex. (B) Ag(NH3 )2 is a weaker oxidising reagent than Ag+. (C) In absence of NH3 silver salt of gluconic acid is formed. (D) NH3 has affected the standard reduction potential of glucose/gluconic acid electrode.
Paragraph for Question Nos. 31 to 33 (3 questions) Chemical reactions involve interaction of atoms and molecules. A large number of atoms/molecules (approximately 6.023 × 1023) are present in a few grams of any chemical compound varying with their atomic/molecular masses. To handle such large numbers conveniently, the mole concept was introduced. This concept has implications in diverse areas such as analytical chemistry, biochemistry, electrochemistry and radiochemistry. The following example illustrates a typical case, involving chemical/ electrochemical reaction, which requires a clear understanding of the mole concept. A 4.0 molar aqueous solution of NaCl is prepared and 500 mL of this solution is electrolysed. This leads to the evolution of chlorine gas at one of the electrodes (atomic mass : Na = 23, Hg = 200; 1 Faraday = 96500 coulombs) [JEE 2007] 3 1 . The total number of moles of chlorine gas evolved is (A) 0.5 (B) 1.0 (C) 2.0 (D) 3.0 3 2 . If the cathode is a Hg electrode, the maximum weight (g) of amalgam formed from this solution is (A) 200 (B) 225 (C) 400 (D) 446 3 3 . The total charge (coulombs) required for complete electrolysis is (A) 24125 (B) 48250 (C) 96500 (D) 193000 Paragraph for Question Nos. 34 & 35 (2 questions) Redox reactions play a pivoted role in chemistry and biology. The values of standard redox potential (E°) of two half-cell reactions decide which way the reaction is expected to proceed. A simple example is a Daniel cell in which zinc goes into solution and copper gets deposited. Given below are a set of half-cell reactions (acidic medium) along with their E° (V with respect to normal hydrogen electrode) values. Using this data obtain the correct explanations to Questions 14-16. I2 + 2e– 2I– E° = 0.54 Cl2 + 2e– 2Cl– E° = 1.36 Mn3+ + e– Mn2+ E° = 1.50 Fe3+ + e– Fe2+ E° = 0.77 O2 + 4H+ + 4e– 2H2O E° = 1.23 [JEE 2007] 3 4 . Among the following, identify the correct statement. (A) Chloride ion is oxidised by O2 (B) Fe2+ is oxidised by iodine (C) Iodine ion is oxidised by chlorine (D) Mn2+ is oxidised by chlorine 3 5 . While Fe3+ is stable, Mn3+ is not stable in acid solution because (A) O2 oxidises Mn2+ to Mn3+ (B) O2 oxidises both Mn2+ to Mn3+ and Fe2+ to Fe3+ (C) Fe3+ oxidises H2O to O2 (D) Mn3+ oxidises H2O to O2 3 6 . Electrolysis of dilute aqueous NaCl solution was carried out by passing 10 milli ampere current. The time required to liberate 0.01 mol of H2 gas at the cathode is (1 Faraday = 96500 C mol–1) (A) 9.65 × 104 sec (B) 19.3 × 104 sec (C) 28.95 × 104 sec (D) 38.6 × 104 sec [JEE 2008] 3 7 . For the reaction of NO3¯ ion in an aqueous solution, E° is +0.96 V. Values of E° for some metal ions are given below V2+ (aq) + 2e¯ V E° = – 1.19 V Fe3+ (aq) + 3e¯ Fe E° = – 0.04 V
Au3+ (aq) + 3e¯ Au E° = + 1.40 V Hg2+ (aq) + 2e¯ Hg E° = + 0.86 V The pair(s) of metal that is(are) oxidised by NO3¯ in aqueous solution is(are) [JEE 2009] (D) Fe and V (A) V and Hg (B) Hg and Fe (C) Fe and Au Paragraph for Questions 38 to 39 The concentration of potassium ions inside a biological cell is at least twenty times higher than the outside. The resulting potential difference across the cell is important in several processes such as transmission of nerve impulses and maintaining the ion balance. A simple model for such a concentration cell involving a metal M is : [JEE 2010] M(s) |M+(aq ; 0.05 molar) || M+(aq ; 1 molar) | M(s) For the above electroly tic cell the magnitude of the cell potential |Ecell| = 70 mV. 3 8 . For the above cell :- (B) Ecell > 0 ; G < 0 (D) Ecell > 0 ; G0 < 0 (A) Ecell < 0 ; G > 0 (C) Ecell < 0 ; G0 > 0 3 9 . If the 0.05 molar solution of M+ is replaced by a 0.0025 molar M+ solution, then the magnitude of the cell potential would be :- (A) 35 mV (B) 70 mV (C) 140 mV (D) 700 mV 4 0 . AgNO3 (aq.) was added to an aqueous KCl solution gradually and the conductivity of the solution was measured. the plot of conductance () versus the volume of AgNO3 is - [JEE 2011] volume volume volume volume (P) (Q) (R) (S) (A) (P) (B) (Q) (C) (R) (D) (S) 4 1 . Consider the following cell reaction : [JEE 2011] 2 F e (s )+ O 2(g )+ 4 H + 2 F e +2+ 2H 2O ( ) E° = 1.67 V (aq) (aq.) At[Fe2+] = 10–3 M, P(O ) = 0.1 atm and pH = 3, the cell potential at 25°C is - 2 (A) 1.47 V (B) 1.77 V (C) 1.87 V (D) 1.57 V Paragraph for Question 42 & 43 The electrochemical cell shown below is a concentration cell. [JEE 2012] M | M2+ (saturated solution of a sparingly soluble salt, MX ) | | M2+ (0.001 mol dm–3) | M 2 The emf of the cell depends on the difference in concentrations of M2+ ions at the two electrodes. The emf of the cell at 298 K is 0.059V.
4 2 . The value of G (kJ mol–1) for the given cell is (take If = 96500 C mol–1) (A) –5.7 (B) 5.7 (C) 11.4 (D) –11.4. 4 3 . The solubility product (Ksp ; mol3 dm–9) of MX2 at 298 K based on the information available for the given concentration cell is (take 2.303 × R × 298/F = 0.059 V) (A) 1 × 10–15 (B) 4 × 10–15 (C) 1 × 10–12 (D) 1 × 10–12 JEE-[MAIN] : PREVIOUS YEAR QUESTIONS ANSWER KEY EXERCISE -5[B] 10 11 12 13 14 15 Que. 1 2 3 4 5 6 7 8 9 Ans. C B A A B C B C A C B B B A D 1 6 . = 94.8% ; Cathode : 2H+ + 2e– H, Anode : Mn2+ Mn4+ + 2e– 2 1 7 . W = 272.2 g, area = 1.02 × 104 cm2 1 8 . K = 7.6 × 1012 1 9 . K = 6.26 × 107 Ag c C 2 0 . K = 2.287 × 10–12 M–3 2 1 . 7.95 × 10–5 M 2 2 . decrease with time sp 2 3 . H0 = –49987 J mol–1, S0 = – 96.5 J mol–1 K–1, s = 1.47 × 10–5 M 24. 0.05 2 5 . K = 1010 2 7 . 55 S m–1 C 2 6 . (a) E0 = 0.59 V, log K = – 10 10 SP (b) 52.8, 10–6 moles 28. A 29. A 30. D 31. B 32. D 33. D 34. C 35. D 36. B 37. A,B,D 38. B 39. C 40. D 41. D 42. D 43. B
EXERCISE-01 CHECK YOUR GRASP SELECT THE CORRECT ALTERNATIVE (ONLY ONE CORRECT ANSWER) 1 . The correct order of reactivity towards the electrophilic substitution of the compounds aniline (I), benzene (II) and nitrobenzene (III) is :- (A) III > II > I (B) II > III > I (C) I < II > III (D) I > II > III 2 . Which of the following order is correct for the decreasing reactivity to ring monobromination of the following compounds :- CH3 COOH NO2 I II III IV (A) I > II > III > IV (B) II > III > IV > I (C) I > III > II > IV (D) III > I > II > IV 3 . Electrophile N O2 attacks the following : CCl3 NO2 CHO O (A) (II) (III) (IV) in which cases N O2 will attack at meta position (A) II and IV (B) I, II and III (C) II and IV (D) I only (D) –CCl3 4 . The strongest deactivating effect on aromatic ring is (A) –CH2Cl (B) –OCH3 (C) –CH3 5 . Which of the following is maximum reactive for nitration is :- (A) (B) (C) (D) 6 . The order of decreasing rectivity towards electrophilic reagent for the following : (a) Benzene (b) Toluene (c) Chloro benzene (d) Anisole (A) b > d > a > c (B) d > c > b > a (C) d > b > a > c (D) a > b > c > d 7 . Increasing order of the following for electrophilic substitution reaction as – –CH3 –COOH ( I ) ( I I ) ( I II ) (A) I < II < III (B) III < II < I (C) II < III < I (D) I < III < II 8 . Among the compounds : CH3 OCH3 CF3 (I) (II) (III) (IV) (D) I > II > III > IV the order of decreasing reactivity towards electrophilic substition is : (A) II > I > III > IV (B) III > I > II > IV (C) IV > I > II > III
9 . Choose the most reactive among the following compound : (A) (B) (C) (D) 1 0 . The number of possible dichloronitrobenzene isomers is : (A) 3 (B) 4 (C) 6 (D) 8 1 1 . The major product formed on monobromination of phenylbenzoate is : Br (B) (A) O Br O O O Br O (D) O (C) O O Br 1 2 . The major product formed in the reaction is : —OCH3 + E+ (electrophile) (A) —OCH3 (B) E— —OCH3 E (C) —OCH3 (D) —OCH3 E E 1 3 . The electrophilic aromatic substitution of a compound C6H5Y produces mainly a meta-disubstituted product. Among the following which one could be the substituent Y ? (A) —NH2 (B) —COOH (C) —CH3 (D) —OCH3 1 4 . Which of the following is an o-, p-directing but deactivating substituent in an electrophilic aromatic substitution : (A) —CCl3 (B) —Cl (C) —NHCOCH3 (D) —OCH3 1 5 . The major product formed in the reaction is : OMe + (CH3)2 CHCH2Br AlCl3
OMe OMe (A) (B) CH2 CH(CH3)2 (CH3)2CHCH2 OMe OMe (C) (D) C(CH3)3 (CH3)3C 1 6 . The dipole moment of chlorobenzene is 1.6 D. The expected dipole moment of meta-dichlorobenzene is: (A) 1.6 D (B) 3.2 D (C) 1.6 2 D (D) 0.0 D 1 7 . In the nitration of benzene with a mixture of concentrated HNO3 and concentrated H2SO4, the active species involved is : (A) N O – (B) NO2 (C) N O – (D) NO 3 2 2 1 8 . Which of the following substituted benzene derivatives would produce three isomeric products when one more substituent is introduced ? Cl Cl Cl Cl Cl Cl Cl (I) (II) (III) (IV) (A) I, II and III (B) I and III (C) II and IV (D) I and IV 1 9 . In the sulphonation of benzene, the active electrophilic speices is : (A) SO2 (B) SO3 (C) S O 2 (D) H SO 4 4 2 0 . The Friedel-Crafts reaction of benzene with n-butyl chloride at 0°C produces : (A) C6H5—CH2CH2CH2CH3 CH3 (B) C6H5CH—CH2CH3 (C) C6H5—CH2—CH—CH3 (D) all of these CH3 2 1 . Sulfonation differs from most of electrophilic aromatic substitution reactions with the fact that the reaction- (A) is reversible (B) requires Lewis acid as catalyst (C) is explosive (D) takes place at high temperature 2 2 . Cumene on treatment with KMnO4 gives - H3C COOH COOH CHO COOH (A) (C) (D) (B)
2 3 . Benzene reacts with CH3COCl in the presece of anhyd. AlCl3 to give : (A) C6H5CH3 (B) C6H5Cl (C) C6H5O2Cl (D) C6H5COCH3 CH3 24. Br2 A (Major product), F e B r2 then the major product A is - CH3 CH3 CH3 CH3 CH3 (C) (D) + Br Br (B) (A) Br Br Br CH3 50% 50% 2 5 . Arrange the following in correct activating order towards EAS - —NHCOCH3 O —NH2 I + IV —O—C—CH3 —NR3 II III (A) III < I < II < IV (B) IV < I < II < III (C) III < II < I < IV (D) II < III < I < IV CHECK YOUR GRASP ANSWER KEY EXERCISE -1 Que. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Ans. D C B D B C B B B C D C B B D Que. 16 17 18 19 20 21 22 23 24 25 Ans. A D B B A A B D A C
EXERCISE–02 BRAIN TEASERS SELECT THE CORRECT ALTERNATIVES (ONE OR MORE THEN ONE CORRECT ANSWERS) 1 . Which of the following groups are m-directing : (A) —CHO (B) —OH (C) —OCOCH3 (D) —COOH 2 . Amongst the ions the aromatic species are : H H H H (A) (B) (D) (C) 3 . The following three isomeric tribromobenzenes are subjected to mononitriation, which is/are given two isomers : Br Br Br Br Br Br Br Br (I) (III) Br (II) Which of these would produce three possible mononitrotribromobenzenes : (A) II and III (B) I and II (C) II (D) III 4 . In the reaction the major product formed is : O N— Br2(1mole) Fe Br O O (A) N— N— (B) Br O O N— (D) N— Br (C) Br 5 . The major product formed in the reaction is : + HNO3 conc.H2SO4 NO2 NO2 (D) (A) (B) (C) NO2 NO2
6 . Nitrobenzene reacts with Br2 in the presence of FeBr3 to give m-bromonitrobenzene as the major product. Which of the following provides the best reason for the formation of m-bromonitrobenzene as the major product : (A) The electron density at the meta position is greater than those at the ortho and para positions (B) Aromaticity is lost in the -complexes formed by the attack of Br+ at the ortho and para positioins but not at the meta position. (C) The -complex formed by the attack of Br+ at the meta position is the least destabilized and the most stable among the three -complexes (D) In the final step of regeneration of benzene ring by the loss of H+ from the -complexes, the meta- oriented -complex loses H+ most readily 7 . Isopropylbenzene can be prepared by : (A) Benzene + CH3CH = CH2 H2SO4 (B) Benzene + CH3—CH—CH3 H2SO4 Cl (C) Benzene + CH3CH—CH3 AlCl3 (D) Benzene + CH3CH2CH2Cl AlCl3 Cl 8 . Which of the following characteristic does an aromatic compound exhibit : (A) It should have (4n +2) -electrons in the ring (B) It should be planar and conjugated (C) It should have 4n -electrons in the ring (D) It should possess high resonance energy 9 . Which of the following groups are meta-directing : (A) —NH2 (B) —OH (C) —NO2 (D) —CN 1 0 . Which of the following groups are ortho-and para-directing : (A) —OH (B) —CHO (C) —CN (D) —NHCOCH3 1 1 . Which of the following statements are correct : (A) An activating group is an electron-releasing group (B) An activating group activates all positions of the benzene ring (C) The effect of any group–whether activating or deactivating–is the strongest at the ortho-and para-positions in the benzene ring (D) An activating group activates only the ortho-and para-positions in the benzene ring 1 2 . The major products formed in the reaction of toluene with chlorine in the presence of ferric chloride are: (A) o-chlorotoluene (B) m-chlorotoluene (C) p-chlorotoluene (D) benzyl chloride 1 3 . Benzene can undergo : (A) substitution (B) addition (C) elimination (D) oxidation 1 4 . Which of the following statements about the nitration of aromatic compounds are correct : (A) The rate of nitration of toluene is greater than that of benzene (B) The rate of nitration of benzene is almost the same as that of hexadeutrobenzene (C) The rate of nitration of benzene is greater than that of hexadeutrobenzene (D) Nitration is an electrophilic substitution reaction
1 5 . Halogenation of benzene in presence of AlCl3 (anhy.) is : (A) nucleophilic substitution (B) nucleophilic addition (C) electrophilic substitution (D) free radical substitution 1 6 . Which of the following structures correspond to the product expected, when excess of C6H6 reacts with CH2Cl2 in presence of anhydrous AlCl3 ? C1 (B) —CHCl2 (A) —CH— Cl (D) —CH2— (C) —C— Cl 1 7 . Select the incorrect statement among the following : (A) benzene undergoes predominantly electrophilic substition reactions (B) toluene is more easily sulphonated than benzene (C) benzene reacts with CCl4 in the presence of anhydrous AlCl3 to give triphenyl methyl chloride (D) benzene reacts with chlorine (Cl2) in presence of light to give benzyl chloride 1 8 . Identify the correct order of reactivity in electrophilic substitution reactions of the following compounds: C2H5 Cl NO2 Cl NO2 (I) (II) (III) (IV) (A) I > II > III > IV (B) IV > III > II > I (C) II > I > III > IV (D) II > III > I > IV 1 9 . The structure of Wheland intermediate obtained after the attack of Br+ on anilinium ion is : H Br + + + H NH3 Br NH3 (A) + (B) H Br + + + H NH3 Br NH3 (C) + (D)
OO 2 0 . Conjugation of electron withdrawing groups, e.g., —CHO, —C—R, —C—OR,—CN, —NO2 activates nucleophilic attack in halobenzene. The order of reactivity of these groups is : O OO (A) —NO2 >—C N > —C—H > —C—R> —C—OR OOO (B) —C—H> —C—R> —C—OR > —C N >—NO2 OOO (C) —C N >—NO2 > —C—H> —C—R> —C—OR O OO (D) —C—H>—NO2 >—C N > —C—OR> —C—R BRAIN TEASERS ANSWER KEY 10 11 EXERCISE -2 A,D A ,B,C 12 13 14 15 Que. 1 2 3 4 5 6789 A A ,B,D A ,B,D C An s . A B,C D D B C A,C ,D A,B,D C,D Que. 16 17 18 19 20 An s . D C ,D C B A
EXERCISE–03 MISCELLANEOUS TYPE QUESTIONS TRUE OR FALSE : 1 . Substitution of benzene occurs through nucleophilic attack. 2 . AlCl3 (aq.) is used as catalyst in Friedel-Crafts reaction. 3 . Diphenyl methane is obtained when excess benzene is treated with dichloro methane in presence of anhy- drous AlCl3. 4 . —NH2 gives ortho-methyl aniline when treated with CH3Cl in presence of AlCl3 (anhydrous). 5 . —CCl3 and —Cl are the meta director. FILL IN THE BLANKS : 1 . Give the structure of the electrophile formed as per the major product : (i) FeBr3 + Br2 .................. (ii) HNO 3 H2SO 4 .................. conc. conc. (iii) SO3 H2SO4 .............. (iv) CH3Cl + AlCl3 .................. fu min gsulphuricacid (v) CH3—CHCH2Cl + AlCl3 .................. CH3 2 . Write the structure of -complex (carbocation) in the following SE reactions : (i) + SO3 .................. (ii) + NO2 .................. neutral Column-II Arenes and alkyl halides in 3 . Write hybridisation of carbon atoms as indicated : presence of anhydrous AlCl d (a) .................. 3 (b) .................. ab CH3 (c) .................. Aromatic compounds c (d) .................. Delocalization of -electrons Deactivates the ring towards MATCH THE COLUMN (p) electrophilic substition 1 . Match the column I with column II. (q) Column-I (r) ( A ) Cyclic conjugated polyenes with (s) (4n + 2) -electrons ( B ) Dichlorobenzene ( C ) Friedel crafts reaction ( D ) Meta directing group
2 . Match the column I with column II. Column-II Column-I (orientation of attacking electrophile) (Compounds) ( p ) Meta position with respect to –NO2 Me ( q ) ortho with respect to methyl group (A) ( r ) only one mono substituted product Me NO2 ( s ) meta with respect to –CH3 (B) NO2 NO2 (C) Me NO2 (D) ASSERTION & REASON QUESTION : These questions contains, Statement-I (assertion) and Statement-II (reason). (A) Statement-I is True, Statement-II is True ; Statement-II is a correct explanation for Statement-I (B) Statement-I is True, Statement-II is True ; Statement-II is NOT a correct explanation for Statement-I (C) Statement-I is True, Statement-II is False. (D) Statement-I is False, Statement-II is True. 1 . Statement-I : In nitration H2SO4 is used as sulphonating agent. Because Statement-II : Benzene has multicentre -bonding. 2 . Statement-I : C2H5 is a meta-directing group. Because Statement-II : The groups which direct the incoming group to meta position are called meta-directing groups. 3 . Statement-I : Tropylium cation is aromatic in anture. + Because Statement-II : The only property that determines its aromatic behavior is its planar structure. 4 . Statement-I : Benzene on heating with conc. H2SO4 gives benzene sulphonic acid which when heated with superheated steam under pressure gives benzene. Because Statement-II : Sulphonation is a reversible process.
5 . Statement-I : Chlorination of ethyl benzene with Cl2 in prescence of heat and light nearly yield 1-chloro- 1-phenyl ethane as major product. Because • Statement-II : The reaction occurs through intermediate formation of the radical C6H5 C H — CH3 . 6 . Statement-I : Nitration of toluene is easier than benzene. Because Statement-II : The methyl group in touene is electron-releasing. 7 . Statement-I : Benzene reacts with n-propyl chloride in presence of AlCl3/ to give isopropyl benzene. Because Statement-II : Benzene undergoes electrophilic substitution readily. 8 . Statement-I : Most o-, p -directing substitution are deactivating. Because Statement-II : o-, p-directors have at least one lone pair of non-bonding electrons. 9 . Statement-I : Nitrobenzene does not undergo Friedel-Craft's reaction. Because Statement-II : Nitrogroup is a deactivating group. 1 0 . Statement-I : The rate of nitration of benzene is less than hexa deutero benzene. Because Statement-II : Deuterium is an isotope of hydrogen. COMPREHENSION BASED QUESTIONS : Comprehension # 1 The typical reaction of benzene and other aromatic compounds are electrophilic substitution. Presence of electron donating group activates the ring towards electrophilic substitution, while presence of electron withdrawing group deactivates the ring towards electrophilic substitution but at the same time activates the ring towards nucleophilic substitution. Some groups are predominantly meta-directing and all of these are deactivating. Except halogen, most of the o-and p-directing groups are activating groups. 1 . C2H5Cl,AlCl3 (A) major. A is trisubstituted benzene. The structure of A is : C2H5 C2H5 C2H5 (B) C2H5 (A) H5C2 C2H5 C2H5 CH2CH2CH2CH3 (D) (C) H5C2 C2H5
O 2. + O AlCl3 (A) H2SO4 (B) + (C) (i) Zn –Hg/ HCl D + E D and E are : (A) (ii ) Se, O and (B) and (C) and (D) and 3 . Which of the following compound is not formed. CH2CH3 (i ) NBS,CCl4 ,hv (X) (ii ) Br2 / FeBr3 X represents mixture of organic compounds. The mixture does not contain. Br CH—CH3 Br C2H5 CH—CH3 (A) (B) Br (C) Br (D) all of them Br Br Comprehension # 2 It is not always easy to predict the position of attack on multiply substituted benzene. If the benzene ring bears different ortho/para directing group at the 1 and 4 positions, the position of further substitution is not immediately clear. Sometimes steric effects determine the outcome. In other cases, electronic factors determine the outcome, and further reaction will be at the position activated by the more strongly activating group. Some substituens are so strongly activating that no catalyst is needed, and it is often difficult to stop substitution after mono substitution. Mild conditions are needed to restrict the reaction to mono-substitution.
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