Fundamentals of Electrochemistry (original) (raw)

Che tn L 3 Electrochemistry 16 numericals

1.♦A♦1♦B♦1 2♦A♦2♦B♦2♦◙11╩N(i)♠10od♠ 3♦A♦3♦4ACWS♠10od♠. Given that, the standard electrode potentials (E°) of metals are í µí°¾ + /í µí°¾ = − 2.93 í µí±‰; í µí° ¶í µí±¢ 2+ / í µí° ¶í µí±¢ = 0.34 í µí±‰, í µí° ¶í µí±Ÿ 3+ / í µí° ¶í µí±Ÿ = − 0.74í µí±‰, í µí°´í µí±” + /í µí°´í µí±” = 0.80 í µí±‰ ; í µí±€í µí±” 2+ /í µí±€í µí±” = − 2.37í µí±‰ ; í µí°¹í µí±’ 2+ / í µí°¹í µí±’ = − 0.44 í µí±‰ Arrange these metals in an increasing order of their reducing power. Ans3. Metals in an increasing order of their reducing power. í µí°´í µí±” + /í µí°´í µí±”; í µí° ¶í µí±¢ 2+ / í µí° ¶í µí±¢; í µí°¹í µí±’ 2+ / í µí°¹í µí±’, í µí° ¶í µí±Ÿ 3+ / í µí° ¶í µí±Ÿ; í µí±€í µí±” 2+ /í µí±€í µí±”, í µí°¾ + /í µí°¾ Ag < Cu < Fe < Cr < Mg < K (More negative E° means that the redox couple is a stronger reducing agent). 4♦A♦4♦7╩N♦The standard reduction potential for Zn 2+ (aq)/Zn(s) is – 0.76 V. Write the reactions occurring at the electrodes when coupled with NHE or SHE (standard hydrogen electrode). Ans4: Zn ⎯→ Zn 2+ + 2e – is reaction at anode when Zn is coupled with NHE or SHE (Standared Hydrogen Electrode).2H + + 2e – ⎯→ H 2 at cathode. 5♦A♦5♦♦8╩N♦E° (reduction potential) of Cu and Zn are + 0.34 V and – 0.76 V respectively. Which of them is stronger reducing agent? Ans5: Zn is stronger reducing agent because it has lower standard reduction potential than that of Cu. 6♦A♦6♦10╩♦. If E° for the reaction Fe 3+ (aq) + e – →Fe 2+ (aq) is + 0.77 V, what will be E°value for the reaction 2Fe 3+ (aq) + 2e –→ 2Fe 2+ (aq)? Ans6: E° = 0.77 V, i.e. e.m.f. of cell will remain the same for reaction 7♦A♦7♦☼PrOH10☼. Iron may be protected from rusting by coating with zinc or tin. By ref ring to the data given below, explain why zinc protects iron more effectively than tin once the protection coating has been scratched. í µí±í µí±› 2+ + 2í µí±’ − ⟶ í µí±í µí±› − 0.76 í µí±‰ ; í µí°¹í µí±’ 2+ + 2í µí±’ − ⟶ í µí°¹í µí±’; −.044; í µí±†í µí±› 2+ + 2í µí±’ − ⟶ í µí±†í µí±› −0.14 í µí±‰ Ans7. Oxidation potentials of zinc, iron and tin will be + 0 76 V, + 0 44 V and + 0 14 V respectively. Thus, oxidation potential of iron is greater than that of tin but less than that of zinc. Thus, out of zinc and i on, zinc is more easily oxidized whereas out of tin and iron, iron is more easily oxidized. Hence, zinc protects more effectively than tin once the iron is exposed (i.e., coating is scratched). DEPICTION OF CELL 'While writing a cell, the anode is written on the left and the cathode on the right. A vertical line separates the metal from the metal ion (electrolyte solution) and a double vertical line indicates a salt bridge which is written between the two half-cells (two electrolytes). The state of the metal and the solution is written with the concentration of the electrolyte in parenthesis. 8♦C♦1♦15╩N♦. Write the correct representation of cell: 2Cr(s) + 3Cd 2+ (aq) ⎯→ 2Cr 3+ (aq) + 3Cd(s) Ans1: Cr(s)|Cr 3+ (aq) ||Cd 2+ |(aq)Cd(s) 9♦C♦2♦1╩N♠13d♦. Represent the galvanic cell in which the reaction is Zn(s) + Cu 2+ (aq) ⎯→ Zn2 + (aq) + Cu(s) Ans2: ♦1╩N♠13d♦ Zn | ZnSO 4 (1M) || CuSO 4 (1M)| Cu(s) 10♦C♦3♦EP♦33♦.Depict the galvanic cell in which cell reaction is Cu + 2Ag + → 2Ag + Cu 2+ Ans3: ♦EP♦33♦Cu|Cu 2+ || Ag + |Ag 11♦C♦4♦B♦3♠8d,8od♠ 12♦C♦5♦25acws♠11dc♠. (I) Write the formulation for the galvanic cell in which the reaction Cu (s) + 2Ag + (aq)⟶ Cu 2+ (aq) + 2Ag (s) takes place. Identify the cathode and the anode reactions in it. Ans5: (I) Cu(s) ⟶ Cu2(aq)+2í µí±’ − [At anode] 2Ag (aq) +2e — 2Ag(s) [At cathode] Cu(s)+2Ag + ⟶(aq) Cu 2+ (aq)+2Ag(s) Cu is acting as anode whereas Ag is acting as cathode. 13♦C♦6♦PROE2♦.A cell is prepared by dipping a copper rod in 1 M CuSO 4 solution and a nickel rod in 1 M NiSO 4 solution. The standard reduction potentials of copper electrode and nickel electrode are 0-34 volt and −0-25 volt respectively.