Electrochemistry Exercise # 2

Exercise # 2 Part # I [Multiple Correct Choice Type Questions] 1. Mark out the correct statement(s) (A) Copper metal cannot reduce iron (II) ions in acidic solutions. (B) Sodium can be obtained by the electrolysis of aqueous solution of NaCl using Pt electrodes. (C) The current carrying ions in an electrolytic cell are not necessarily discharged at the electrodes. (D) Cations having more negative oxidation potential than – 0.828 V are reduced in preference to water. 2. Mark out the correct statement(s) regarding electrolytic molar conductivity. (A) It increase as temperature increases. (B) It experiences resistance due to vibration of ion at the mean position. (C) Increase in concentration decreases the electrolytic molar conductivity of both the strong as well as the weak electrolyte. (D) Greater the polarity of solvent, greater is the electrolytic molar conduction. 3. If same quantity of electricity is passed through three electrolytic cells containing FeSO4, Fe2(SO4)3 and Fe(NO3)3, then (A) the amount of iron deposited in FeSO4 and Fe2(SO4)3 are equal (B) the amount of iron deposited in FeSO4 is 1.5 times of the amount of iron deposited in Fe(NO3)3. (C) the amount of iron deposited in Fe2(SO4)3 and Fe(NO3)3 are equal (D) the same amount of gas is evolved in all three cases at the anode. 4. When a cleaned strip of zinc metal is placed in a solution of CuSO4 , a spontaneous reaction occurs . Which of the following observation(s) is/are made ? (A) the mass of zinc metal decreases gradually (B) the copper metal starts depositing on either zinc plate or settles down to the vessel (C) the solution remains electrically neutral (D) the temperature of the solution decreases as it is an endothermic reaction. 5. In the electrolysis of aqueous CuBr2 using Pt electrodes : (A) Br2 gas is evolved at the anode (B) Cu (s) is deposited at the cathode (C) Br2 gas is evolved at anode and H2 gas at cathode (D) H2 gas is evolved at anode. 6. 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 . 7. Which of the following statements is / are correct ? (A) The conductance of one cm3 (or 1 unit3) of a solution is called conductivity. (B) Specific conductance increases while molar conductivity decreases on progressive dilution. (C) The limiting equivalent conductivity of weak electrolyte cannot be determine exactly by extrapolation of the plot of eq against c . (D) The conductance of metals is due to the movement of free electrons. ELECTROCHEMISTRY 8. When galvanic cell started, with passage of time (A) spontaneity of the cell reaction decreases; Ecell decreases (B) reaction quotient Q decreases; Ecell increases (C) reaction quotient Q increases; Ecell decreases (D) at equilibrium Q = Kc; Ecell = 0. 9. Stansdard electrode potential are Eº Fe 2  | Fe = – 0.44 V, Eº Fe 3  then (A) Fe3+ increases 10. 11. (B) Fe3+ decreases = 0.77 V. If Fe, Fe2+ and Fe3+ are kept together,, (C) Fe2+ increases (D) Fe2+ decreases In which of the following cell (s) : Ecell=Ecell0 ? (A) Cu(s) Cu 2+ (0.01M) Ag + (0.1M) Ag(s) (B) Pt(H ) pH = 1 Zn 2 + (0.01 M) Zn(s) 2 (C) Pt(H 2 ) pH = 1 Zn 2+ (1M) Zn(s) (D) Pt(H 2 ) H + = 0.1M Zn 2+ (0.01M) Zn(s) The reaction : 1/2H2(g) + AgCl(s)  H+(aq) + Cl–(aq) + Ag(s) occurs in the galvanic cell – (A) Ag | AgCl(s) | KCl (soln) | AgNO3 (soln) | Ag (C) Pt | H2(g) | HCl (soln) | AgCl(s) | Ag 12. | Fe 2  (B) Pt | H2(g) | HCl (soln) | AgNO3 (soln) | Ag (D) Pt | H2(g) | KCl (soln) | AgCl(s) | Ag Choose the correct statement(s). (A) At the anode, the species having minimum reduction potential is formed from the oxidation of corresponding oxidizable species. (B) In highly alkaline medium, the anodic process during the electrolytic process is 4OH–  O2 + 2H2O + 4e– . (C) The standard potential of Cl– |AgCl| Ag half-cell is related to that of Ag+ | Ag through the expression RT E oAg |Ag = E o  + ln Ksp(AgCl) Cl | AgCl|Ag F (D) Compounds of active metals (Zn, Na, Mg) are reducible by H2 whereas those of noble metals (Cu, Ag, Au) are not reducible. 13. 14. M(s)  Mn+ (aq) + ne– Choose the correct statement(s). (A) E M | M n+ decreases with increase in [Mn+] (B) E M n+ | M increases on increasing temperature. (C) E M n+ | M increases on increasing [Mn+] (D) E M | M n+ increases on increasing temperature. Which is/are correct among the following ? Given, the half cell emf’s E 0 +2 = 0.337, E0 +1 = 0.521 Cu |Cu Cu |Cu (A) Cu+1 disproportionates (B) Cu and Cu2+ comproportionates. (C) E 0Cu | Cu +2 + E 0Cu +1 | Cu is positive (D) All of these Part # II [Assertion & Reason Type Questions] Each question has 5 choices (A), (B), (C), (D) and (E) out of which only one is correct. (A) Statement-1 is true, Statement-2 is true and Statement-2 is correct explanation for Statement-1 (B) Statement-1 is true, Statement-2 is true and Statement-2 is not correct explanation for Statement-1 (C) Statement-1 is true, Statement-2 is false (D) Statement-1 is false, Statement-2 is true (E) Both Statements are false 1.  dE cell  Statement-1 : If  dT  > 0 for a cell reaction then S is positive.  p  dE  Statement-2 : S = nFT  dT  .  p 2. Statement-1 : If an aqueous solution of NaCl is electrolysed, the product obtained at the cathode is H2 gas and not Na. Statement-2 : Gases are liberated faster than the metals during the electrolysis of an electrolyte. 3. Statement-1 : When 2 faraday of electricity is passed through 0.1 M H2SO4 (aq), 11.2 litre O2 evolved at STP. Statement-2 : Molecular weight of oxygen is 32. 4. Statement-1 : The electrode potential of SHE is zero only at 25° C and not on other temperature. Statement-2 : SHE is a standard reference electrodes. 5. Statement-1 : Absolute value of E0red of an electrode cannot be determined. Statement-2 : Neither oxidation nor reduction can take place alone. 6. Statement-1 : Eºcell = 0 for a chloride ion concentration cell. Statement-2 : For this concentration cell where Ecell = 7. [Cl – ]LHS RT ln [Cl – ]RHS nF Statement-1 : Molar conductivity increases with decreases in concentration for weak electrolytes. Statement-2 : No. of ions per unit volume decreased due to dilution. 8. Statement-1 : Conductivity always decreases with the decreased in concentration both the weak and strong electrolytes. Statement-2 : No. of ions per unit volume linearly decreases in both electrolytes. 9. Statement-1 : Gold chloride (AuCl3) solution cannot be stored in a vessel made of copper, iron, nickel chromium, zinc or tin. Statement-2 : Gold is very precious metal. 10. Statement-1 : Copper is dissolved at anode and deposited at cathode when Cu electrodes are used and electrolyte is 1 M CuSO4 (aq) solution. Statement-2 : SOP of Cu is less than SOP of water and SRP of Cu is greater than SRP of water. 11. Statement-1 : Molar conductivity of a weak electrolyte at infinite dilution cannot be determined experimentally. Statement-2 : Kohlrausch law help to find the molar conductivity of a weak electrolyte at infinite dilution. ANSWER KEY EXERCISE - 2 : PART # I 1. A, C,D 2. A, C, D 3. B, C, D 4. A, B, C 11. C, D 12. A, B 13. A, B, C 14. A, C 5. A, B 6. A,B 7. A, C, D 8. A, C, D PART # II 1. D 2. B 3. B 4. C 5. C 6. B 7. B 8. C 9. B 10. A 11. C 9. B, C 10. A, B, D