Free NEET Chemistry multiple-choice questions on Electrochemical Cells. Attempt each question and reveal the answer with a full explanation.
Which of the following is NOT a function of a salt bridge? To increase the EMF of the cell To maintain electrical neutrality To complete the circuit To prevent liquid-liquid junction potential Which of the following is the correct cell representation for the reaction Mg(s) + 2Ag +(aq) Mg 2+ (aq) + 2Ag(s) ? Mg | Mg 2+ || Ag + | Ag Ag | Ag + || Mg 2+ | Mg Mg | Ag + || Mg 2+ | Ag Mg 2+ | Mg || Ag | Ag + The standard reduction potentials for Mg 2+ /Mg is -2.37 V and Cl 2/Cl - is +1.36 V . The standard EMF of the cell Mg | Mg 2+ || Cl 2 | Cl - is: 3.73 V 1.01 V -3.73 V -1.01 V The amount of energy expended to decompose 1 mol of H 2O into H 2 and 1/2 O 2 under standard conditions is related to the cell potential by: G = -nFE H = nFE S = nFE W = V I If E Fe 2+ /Fe = -0.441 V and E Fe 3+ /Fe 2+ = 0.771 V , the standard EMF of the reaction : Fe + 2Fe 3+ -> 3Fe 2+ will be: 0.330 V 1.653 V 1.212 V 0.111 V A button cell used in watches functions as following Zn(s) + Ag2O(s) + H2O(l) <=> 2Ag(s) + Zn 2+ (aq) + 2OH - (aq) If half cell potentials are Zn 2+ (aq) + 2e - -> Zn(s) ; E = -0.76 V Ag2O(s) + H2O(l) + 2e - -> 2Ag(s) + 2OH - (aq) , E = 0.34 V The cell potential will be 1.10 V 0.42 V 0.84 V 1.34 V The electrode potentials for Cu 2+ (aq) + e - Cu +(aq) and Cu +(aq) + e - Cu(s) are +0.15V and +0.50V respectively. The value of E Cu 2+ /Cu will be: 0.325V 0.650V 0.150V 0.500V Calculate the standard free energy change G for the reaction Zn(s) + Cu 2+ (aq) Zn 2+ (aq) + Cu(s) , given E cell = 1.1V . -212.3 kJ -106.1 kJ +212.3 kJ -21.23 kJ The standard reduction potential for the half-reactions are: Zn 2+ + 2e - Zn ( E = -0.76 V ) and Fe 2+ + 2e - Fe ( E = -0.44 V ). Which of the following is correct? Zn can reduce Fe 2+ Fe can reduce Zn 2+ Zn 2+ can reduce Fe Fe 2+ can reduce Zn In a H 2-O 2 fuel cell, the reaction occurring at the cathode is: O 2(g) + 2H 2O(l) + 4e - 4OH -(aq) 2H 2(g) + 4OH -(aq) 4H 2O(l) + 4e - H 2(g) + 2OH -(aq) 2H 2O(l) + 2e - O 2(g) + 4H +(aq) + 4e - 2H 2O(l) In the Leclanché cell (dry cell), the reduction of manganese occurs in the cathode. The oxidation state of manganese changes from: +4 to +3 +7 to +2 +4 to +2 +6 to +4 The relationship between standard free energy change and standard cell potential is given by G = -nFE cell . Here n represents: Number of moles of electrons exchanged in the balanced equation Number of moles of product formed Number of moles of reactant consumed Valency of the metal electrode The reaction 1/2 H 2(g) + AgCl(s) H +(aq) + Cl -(aq) + Ag(s) occurs in a galvanic cell. The correct cell notation is: Pt(s) | H 2(g, 1 atm) | H +(aq) || Cl -(aq) | AgCl(s) | Ag(s) Pt(s) | H 2(g, 1 atm) | H +(aq) || Ag +(aq) | Ag(s) Pt(s) | H 2(g, 1 atm) | Cl -(aq) || Ag +(aq) | Ag(s) Ag(s) | AgCl(s) | Cl -(aq) || H +(aq) | H 2(g, 1 atm) | Pt(s) When E cell < 0 , which of the following is true for the reaction at standard conditions? G > 0 ; the reaction is non-spontaneous G < 0 ; the reaction is spontaneous G = 0 ; the reaction is at equilibrium K eq > 1 In a fuel cell, the efficiency is given by the expression: G / H H / G G / S S / G The standard electrode potential for Sn 4+ /Sn 2+ is +0.15 V and for Cr 3+ /Cr is -0.74 V . The standard cell potential for the cell Cr | Cr 3+ || Sn 4+ | Sn 2+ is: 0.89 V 0.59 V 1.19 V -0.59 V The standard reduction potentials of Zn 2+ /Zn , Cu 2+ /Cu , and Ag +/Ag are -0.76 V, +0.34 V , and +0.80 V respectively. Which of the following reactions is NOT spontaneous? 2Ag + Cu 2+ 2Ag + + Cu Zn + Cu 2+ Zn 2+ + Cu Cu + 2Ag + Cu 2+ + 2Ag Zn + 2Ag + Zn 2+ + 2Ag In the electrolysis of aqueous NaCl , the gas liberated at the cathode is H 2 rather than Na because: Standard reduction potential of H + is higher than Na + Standard reduction potential of Na + is higher than H + Na is highly reactive The overpotential of H 2 is very low Which of the following describes the cathodic protection of iron pipes buried underground? Connecting the iron pipe to a more reactive metal like Magnesium Coating the pipe with a layer of oil Painting the pipe with red lead Connecting the pipe to the positive terminal of a battery Given E Mg 2+ /Mg = -2.37 V and E Fe 2+ /Fe = -0.44 V , which of the following statements is correct? Mg can reduce Fe 2+ ions Fe can reduce Mg 2+ ions Mg is a weaker reducing agent than Fe Fe is more reactive than Mg For a cell Zn | Zn 2+ (1 M) || Cu 2+ (1 M) | Cu , the value of G is approximately (Given E cell = 1.1 V ): -212 kJ/mol +212 kJ/mol -110 kJ/mol +110 kJ/mol The E cell for the reaction 2H 2(g) + O 2(g) 2H 2O(l) is +1.23 V . The value of G for this process is: -474.8 kJ/mol +474.8 kJ/mol -237.4 kJ/mol +237.4 kJ/mol If the salt bridge is removed from a galvanic cell while it is operating, the voltage: Drops to zero Increases Remains constant Fluctuates In a salt bridge, KNO 3 is used because: The transport numbers of K + and NO 3 - are almost equal It is a strong electrolyte It is very soluble in water It does not react with the electrodes A galvanic cell consists of a Zn electrode in 1.0 M ZnSO 4 and a Ag electrode in 1.0 M AgNO 3 . The maximum work that can be obtained from this cell per mole of Zn is: (Given E Zn 2+ /Zn = -0.76 V, E Ag +/Ag = 0.80 V ) 301.1 kJ 150.5 kJ 212.3 kJ 76.5 kJ In a button cell used in watches, the following reaction occurs: Zn(s) + Ag 2O(s) + H 2O(l) Zn 2+ (aq) + 2Ag(s) + 2OH -(aq) . If standard potentials are E Zn 2+ /Zn = -0.76 V and E Ag +/Ag = 0.34 V (for the oxide half-cell, E Ag 2O/Ag = 0.344 V ), the cell potential E cell is: 1.104 V 0.42 V 0.84 V 1.34 V The calomel electrode, used as a reference electrode, consists of a mixture of: Hg and Hg 2Cl 2 in KCl solution Hg and HgCl 2 in KCl solution Pb and PbSO 4 in H 2SO 4 solution Pt and Hg 2Cl 2 in HCl solution Why is Lithium the strongest reducing agent in aqueous solution, despite having the highest ionization enthalpy among alkali metals? It has the highest hydration enthalpy. It has the lowest sublimation enthalpy. It has the smallest atomic size. It has the highest electron gain enthalpy. A salt bridge containing KCl cannot be used in a cell containing which of the following electrodes? Ag/AgNO 3 Zn/ZnSO 4 Cu/CuSO 4 Fe/FeSO 4 In a standard hydrogen electrode (SHE), the platinum foil is coated with 'platinum black' primarily to: Increase the surface area for the adsorption of hydrogen gas. Prevent the oxidation of the platinum metal. Act as a sacrificial anode. Ensure the solution remains at pH 0. Which of the following represents the temperature coefficient of the EMF of a cell? ( E / T) P ( G / T) P ( E / P) T S / nF In the Salt Bridge of a Galvanic cell, the ions of the electrolyte (like KCl ) must have: Nearly equal transport numbers High charge density Different velocities The ability to react with electrode solutions Galvanization is the process of protecting iron from rusting by coating it with zinc. This works because: Zinc has a more negative reduction potential than iron Zinc is less reactive than iron Zinc forms a hard alloy with iron Iron has a more negative reduction potential than zinc The potential of a standard hydrogen electrode (SHE) is zero only when: Pressure of H 2 is 1 bar and [H +] is 1 M at all temperatures Pressure of H 2 is 1 atm and temperature is 273 K [H +] is 10 -7 M Pressure of H 2 is 10 bar and [H +] is 1 M A hypothetical electrochemical cell is shown below: A | A+ (xM) || B+ (yM) | B The emf measured is +0.20V. The cell reaction is: A+ + B -> A + B+ A+ + e- -> A; B+ + e- -> B The cell reaction cannot be predicted A + B+ -> A+ + B Given : (i) Cu 2+ + 2e - -> Cu , E =0.337 V (i) Cu 2+ + e - -> Cu + , E =0.153 V Electrode potential E for the reaction, Cu + + e - -> Cu , will be : 0.38 V 0.52 V 0.90 V 0.30 V The zinc/silver oxide cell is used in electric watches. The reaction is as following, Zn 2+ + 2e - -> Zn ; E 0=-0.760 V Ag2O + H2O + 2e - -> 2Ag + 2OH - ; E 0=0.344 V If F is 96,500 C mol -1 , G 0 of the cell will be 413.021 kJ mol -1 113.072 kJ mol -1 213.072 kJ mol -1 313.082 kJ mol -1 Consider the change in oxidation state of Bromine corresponding to different emf values as shown in the diagram below : Then the species undergoing disproportionation is Br2 BrO4 - BrO3 - HBrO For the cell reaction 2Fe 3+ (aq) + 2I - (aq) -> 2Fe 2+ (aq) + I2(aq) E cell = 0.24 V at 298 K. The standard Gibbs energy ( r G ) of the cell reaction is : [Given that Faraday constant F = 96500 C mol -1 ] 23.16 kJ mol -1 - 46.32 kJ mol -1 - 23.16 kJ mol -1 46.32 kJ mol -1 Given below are half cell reactions: MnO4 - + 8H+ + 5e - -> Mn 2+ + 4H2O E Mn 2+/MnO4 - = -1.510 V 1/2 O2 + 2H+ + 2e - -> H2O E O2/H2O = +1.223 V Will the permanganate ion, MnO4 - liberate O2 from water in the presence of an acid? No, because E cell =-0.287 V Yes, because E cell =+2.733 V No, because E cell =-2.733 V Yes, because E cell =+0.287 V At 298 K, the standard electrode potentials of Cu 2+/Cu , Zn 2+/Zn , Fe 2+/Fe and Ag+/Ag are 0.34 V, -0.76 V, -0.44 V and 0.80 V, respectively. On the basis of standard electrode potential, predict which of the following reaction cannot occur? CuSO4(aq) + Fe(s) -> FeSO4(aq) + Cu(s) FeSO4(aq) + Zn(s) -> ZnSO4(aq) + Fe(s) 2CuSO4(aq) + 2Ag(s) -> 2Cu(s) + Ag2SO4(aq) CuSO4(aq) + Zn(s) -> ZnSO4(aq) + Cu(s) Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R Assertion A : In equation r G = -nFE cell , value of r G depends on n. Reasons R : E cell is an intensive property and r G is an extensive property. In the light of the above statements, choose the correct answer from the options given below. Both A and R are true and R is the correct explanation of A Both A and R are true and R is NOT the correct explanation of A A is true but R is false A is false but R is true Given E MnO 4 -/Mn 2+ = 1.51 V and E MnO 2/Mn 2+ = 1.23 V . The standard potential for the half-reaction MnO 4 - + 4H + + 3e - MnO 2 + 2H 2O is: 1.70 V 0.28 V 2.74 V 0.93 V Calculate the standard free energy change ( G ) for the disproportionation of Cu + in aqueous solution: 2Cu +(aq) Cu 2+ (aq) + Cu(s) . (Given E Cu +/Cu = 0.52 V and E Cu 2+ /Cu + = 0.16 V ) -34.74 kJ/mol -69.48 kJ/mol +34.74 kJ/mol -17.37 kJ/mol Which of the following processes is responsible for the corrosion of iron in the presence of water and air? Formation of an electrochemical cell on the surface of iron Direct reaction of iron with nitrogen Reduction of iron to its metallic form Absorption of water by the iron lattice The standard electrode potential (E°) for the half-cell reaction Fe 3+ + e- -> Fe 2+ at 298 K is (Given : E°( Fe 3+ /Fe) = –0.04 V and E°( Fe 2+ /Fe) = –0.44 V at 298 K) +0.40 V +0.76 V –0.48 V +0.92 V In a galvanic cell, electrons flow from: Anode to Cathode through the external circuit Cathode to Anode through the external circuit Anode to Cathode through the salt bridge Cathode to Anode through the salt bridge For a cell reaction to be spontaneous at constant temperature and pressure, which condition must be satisfied? G < 0 G > 0 E cell < 0 S total < 0 According to the IUPAC convention, the standard hydrogen electrode (SHE) is assigned a potential of: 0.00 V at all temperatures 0.00 V only at 298 K 1.00 V at all temperatures Dependent on the pressure of H 2 gas only A redox reaction is spontaneous if the standard cell potential ( E cell ) and the standard Gibbs free energy change ( G ) are respectively: Positive, Negative Negative, Positive Positive, Positive Negative, Negative