Important questions of Electro Chemistry for IIT – JEE mains & advance

Electro Chemistry is one a very  scoring  chapter for IIT – JEE Main and Advance. So, go through these questions and prepare yourself!

 

Q.1 Calculate the no. of electrons lost or gained during electrolysis of

(a) 3.55 gm of Cl ions         (b) 1 gm Cu2+ ions         (c) 2.7 gm of Al3+ ions

Q.2 How many faradays of electricity are involved in each of the case

(a) 0.25 mole Al3+ is converted to Al.

(b) 27.6 gm of SO3 is convered to SO2− 3

(c) The Cu2+ in 1100 ml of 0.5 M Cu2+ is converted to Cu.

Q.3 0.5 mole of electron is passed through two electrolytic cells in series. One contains silver ions, and the other zinc ions. Assume that only cathode reaction in each cell is the reduction of the ion to the metal. How many gm of each metals will be deposited.

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Q.4 The electrosynthesis of MnO2 is carried out from a solution of MnSO4 in H2 SO4 (aq). If a current of 25.5 ampere is used with a current efficiency of 85%, how long would it take to produce 1 kg of MnO2 ?

Q.5 A constant current of 30 A is passed through an aqueous solution of NaCl for a time of 1.0 hr. How many grams of NaOH are produced? What is volume of Cl2 gas at S.T.P. produced?

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Q.6 If 0.224 litre of H2 gas is formed at the cathode, how much O2 gas is formed at the anode under identical conditions?

Q.7 If 0.224 litre of H2 gas is formed at the cathode of one cell at S.T.P., how much of Mg is formed at the cathode of the other electrolytic cell.

Q.8 Assume 96500 C as one unit of electricity. If cost of electricity of producing x gm Al is Rs x, what is the cost of electricity of producing x gm Mg?

Q.9 Calculate the quantity of electricity that would be required to reduce 12.3 g of nitrobenzene to aniline, if the current efficiency for the process is 50 percent. If the potential drop across the cell is 3.0 volts, how much energy will be consumed?

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Q.10 How long a current of 2A has to be passed through a solution of AgNO3 to coat a metal surface of 80cm2 with 5µm thick layer? Density of silver = 10.8g/cm3

Q.11 A metal is known to form fluoride MF2 . When 10A of electricity is passed through a molten salt for 330 sec., 1.95g of metal is deposited. Find the atomic weight of M. What will be the quantity of electricity required to deposit the same mass of Cu from CuSO4 ?

Q.12 10g fairly concentrated solution of CuSO4 is electrolyzed using 0.01F of electricity. Calculate:

(a)The weight of resulting solution                (b)Equivalents of acid or alkali in the solution.

Q.13 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 was deposited in the copper voltameter in series with the electrolytic cell. Calculate the percentage yield of NaOH obtained.

Q.14 Three electrolytic cells A, B, C containing solution of ZnSO4 , AgNO3 and CuSO4 , respectively are connected in series. A steady current of 2 ampere was passed through them until 1.08 g of silver deposited at the cathode of cell B. How long did the current flow? What mass of copper and of zinc were deposited?

Q.15 Copper sulphate solution (250 mL) was electrolysed using a platinum anode and a copper cathode. A constant current of 2 mA was passed for 16 minutes. It was found that after electrolysis the concentration of the solution was reduced to 50% of its original value. Calculate the concentration of copper sulphate in the original solution.

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Q.16 A solution of Ni(NO3 ) 2 is electrolysed between platinum electrodes using a current of 5 ampere for 20 mintue. What mass of Ni is deposited at the cathode?

Q.17 A current of 3.7A is passed for 6hrs. between Ni electrodes in 0.5L of 2M solution of Ni(NO3 ) 2 . What will be the molarity of solution at the end of electrolysis?

Q.18 Is 1.0 M H+ solution under H2 SO4 at 1.0 atm capable of oxidising silver metal in the presence of 1.0 M Ag+ ion?

Eo Ag+|Ag = 0.80 V, Eo H+|H2 (Pt )  = 0.0 V

Q.19 Calculate the EMF of a Daniel cell when the concentration of ZnSO4 and CuSO4 are 0.001 M and 0.1M respectively. The standard potential of the cell is 1.1V.

Q.20 For a cell Mg(s) | Mg2+(aq) || Ag+ (aq) | Ag, Calculate the equilibrium constant at 25 0C. Also find the maximum work that can be obtained by operating the cell. E 0 (Mg2+/Mg) = −2.37V, E0 (Ag+ /Ag) = 0.8 V.

Q.21 If Eo Fe2+|Fe  = – 0.44 V, Eo  Fe3+|  Fe2+  = 0.77 V. Calculate EoFe3+|Fe .

Q.22 Equinormal Solutions of two weak acids, HA (pKa = 3) and HB (pKa = 5) are each placed in contact with standard hydrogen electrode at 250C. When a cell is constructed by interconnecting them through a salt bridge, find the emf of the cell.

Q.23 In two vessels each containing 500ml water, 0.5m mol of aniline (Kb = 10−9 ) and 25mmol of HCl are added separately. Two hydrogen electrodes are constructed using these solutions. Calculate the emf of cell made by connecting them appropriately.

Q.24 Calculate E0 and E for the cell Sn | Sn2+ (1M) || Pb2+ | Pb(10−3M), E0 (Sn2+| Sn) = −0.14V, E0 (Pb2+| Pb) = −0.13V. Is cell representation is correct?

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Q.25 At what concentration of Cu2+ in a solution of CuSO4 will the electrode potential be zero at 250C? Given : E0 (Cu | Cu2+) = −0.34 V.

Q.26 A zinc electrode is placed in a 0.1M solution at 250C. Assuming that the salt is 20% dissociated at this dilutions calculate the electrode potential. E0 (Zn2+| Zn) = −0.76V.

Q.27 Calculate the EMF of the cell,
Zn – Hg(c1M) | Zn2+ (aq)| Hg – Zn(c2M) at 25°C, if the concentrations of the zinc amalgam are: c1 = 10g per 100g of mercury and c2 = 1g per100 g of mercury

Q.28 The resistance of a conductivity cell filled with 0.01N solution of NaCl is 210 ohm a t 1 8 o C . Calculate the equivalent conductivity of the solution. The cell constant of the conductivity cell is 0.88 cm−1 .

Q.29 The molar conductivity of 0.1 M CH3 COOH solution is 4.6 S cm2 mole−1 . What is the specific conductivity and resistivity of the solution ?

Q.30 The conductivity of pure water in a conductivity cell with electrodes of cross sectional area 4 cm2 and 2 cm apart is 8 x 10−7 S cm−1 . (i) What is resistance of conductivity cell ? (ii) What current would flow through the cell under an applied potential difference of 1 volt?

Q.31 Resistivity of 0.1M KCl solution is 213 ohm cm in a conductivity cell. Calculate the cell constant if its resistance is 330 ohm.

Q.32 Resistance of a 0.1M KCl solution in a conductance cell is 300 ohm and specific conductance of 0.1M KCl is 1.29 x 10-2 ohm-1 cm-1. The resistance of 0.1M NaCl solution in the same cell is 380 ohm. Calculate the equivalent conductance of the 0.1M NaCl solution.

Q.33 For 0.01N KCl, the resistivity 709.22 mho cm. Calculate the conductivity and equivalent conductance.

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Q.34 A solution containing 2.08 g of anhydrous barium chloride is 400 CC of water has a specific conductivity 0.0058 ohm–1cm–1. What are molar and equivalent conductivities of this solution.

Q.35 Same quantity of electricity is being used to liberate iodine (at anode) and a metal x (at cathode). The mass of x deposited is 0.617g and the iodine is completely reduced by 46.3 cc of 0.124M sodium thiosulphate. Find the equivalent mass of x.

Q.36 The emf of the cells obtained by combining Zn and Cu electrode of a Daniel cell with N calomel electrode in two different arrangements are 1.083V and 0.018V respectively at 250C. If the standard reduction potential of N calomel electrode is −0.28V and that of Zn is −0.76 V, find the emf of Daniel cell.

Q.37 The normal potential of Zn referred to SHE is 0.76V and that of Cu is −0.34V at 250C. When excess of Zn is added to CuSO4 , Zn displaces Cu2+ till equilibrium is reached. What is the ratio of Zn2+ to Cu2+ ions at equilibrium?

Q.38 An acidic solution of Cu2+ salt containing 0.4 g 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.

Q.39 In the refining of silver by electrolytic method what will be the weight of 100 gm Ag anode if 5 ampere current is passed for 2 hours? Purity of silver is 95% by weight.

Q.40 Assume that impure copper contains only iron, silver and a gold as impurities. After passage of 140 A, for 482.5s of the mass of the anode decreased by 22.260g and the cathode increased in mass by 22.011 g. Estimate the % iron and % copper originally present.

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ANSWERS 

QUESTION ANSWER QUESTION ANSWER
Q.1 (a) 6.02 × 1022 electrons lost, (b) 1.89 × 1022 electrons gained, (c) (b) 1.80 × 1023 electrons gained Q.20 Kc = 1.864 x 10107 , ∆G0 = – 611.8 kJ
Q.2 (a) 0.75 F, (b) 0.69 F, (c)1.1 F Q.21 – 0.0367 V
Q.3 (i) 54 gm, (ii) 16.35 gm Q.22 E = 0.059
Q.4 1.023 × 105 sec Q.23 E = 0.395 V Q.41 E0 cell = +0.01V, Ecell = −0.0785V, correct representation is Pb|Pb2+ (10−3M)||Sn2+(1M)|Sn Q.42 [Cu2+] = 2.97 x 10−12M for E =0 Q.43 E = −0.81eV
 Q.5 1.12 mol, 12.535 litre Q.24 E0 cell = +0.01V, Ecell = −0.0785V, correct representation is Pb|Pb2+ (10−3M)||Sn2+(1M)|Sn
Q.6 0.112 litre Q.25 [Cu2+] = 2.97 x 10−12M for E =0
Q.7 0.24 gms Q.26 E = −0.81eV
Q.8 Rs. 0.75x Q.27 0.0295 V
Q.9 115800C, 347.4 kJ Q.28 419 S cm2 equivalent –1 1
Q.10 t = 193 sec Q.29 0.00046 S cm−1 ; 2174 ohm cm
Q.11 A = 114, Q = 5926.8C Q.30 (i) 6.25 x 105 ohm, (ii) 1.6 x 10−6 amp
Q.12 Final weight = 9.6g,0.01Eq of acid Q.31 1.549 cm–1
Q.13 60 % Q.32 101.8 ohm-1 cm2 / gm equivalent
Q.14 (i) 482.5 sec (ii) 0.3175 gm (iii) 0.327 gm Q.33 0.0141 mho g equiv-–1 m2 , 0.141 mho m-1
Q.15 7.958 ×10–5M Q.34 (i) 232 Mho cm2 mol–1 , (ii) 116 Mho cm2 equivalent–
Q.16 1.825 g Q.35 Eq. wt. = 107.3
Q.17 2M Q.36 E = 1.1 V
Q.18 – 0.80 V, NO Q.37 [Zn2+]/[Cu2+] = 1.941 x 1037
Q.19 E =1.159V Q.38 V(O2 ) = 99.68 mL, V(H2 ) = 58.46 mL, Total vol. = 158.1 mL

Q.39 0.179 V Q.40 Cu = 98.88%, Fe = 0.85%

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