Chapter 3 Electrochemistry

Question 1. Which cell will measure standard electrode potential of copper electrode?

(i) Pt (s) | H$_{2}$ (g,0.1 bar) | H$^{+}$ (aq.,1 M) || Cu$^{2+}$(aq.,1M) | Cu

(ii) Pt(s) | H$_{2}$ (g, 1 bar) | H$^{+}$ (aq.,1 M) || Cu$^{2+}$ (aq.,2 M) | Cu

(iii) Pt(s) | H$_{2}$ (g, 1 bar) | H$^{+}$ (aq.,1 M) || Cu$^{2+}$ (aq.,1 M) | Cu

(iv) Pt(s) | H$_{2}$ (g, 1 bar) | H$^{+}$ (aq.,0.1 M) || Cu$^{2+}$ (aq.,1 M) | Cu

Question 2. Electrode potential for Mg electrode varies according to the equation $E_{Mg^{2+} | Mg} = E_{Mg^{2+} | Mg}^{\ominus} - \frac{0.059}{2} \log \frac{1}{[Mg^{2+}]}$. The graph of $E_{Mg^{2+} | Mg}$ vs log [Mg$^{2+}$] is

(i)

(ii)

(iii)

(iv)

Question 3. Which of the following statement is correct?

(i) $E_{Cell}$ and $\Delta_rG$ of cell reaction both are extensive properties.

(ii) $E_{Cell}$ and $\Delta_rG$ of cell reaction both are intensive properties.

(iii) $E_{Cell}$ is an intensive property while $\Delta_rG$ of cell reaction is an extensive property.

(iv) $E_{Cell}$ is an extensive property while $\Delta_rG$ of cell reaction is an intensive property.

Question 4. The difference between the electrode potentials of two electrodes when no current is drawn through the cell is called __________.

(i) Cell potential

(ii) Cell emf

(iii) Potential difference

(iv) Cell voltage

Question 5. Which of the following statement is not correct about an inert electrode in a cell?

(i) It does not participate in the cell reaction.

(ii) It provides surface either for oxidation or for reduction reaction.

(iii) It provides surface for conduction of electrons.

(iv) It provides surface for redox reaction.

Question 6. An electrochemical cell can behave like an electrolytic cell when ____________.

(i) $E_{cell} = 0$

(ii) $E_{cell} > E_{ext}$

(iii) $E_{ext} > E_{cell}$

(iv) $E_{cell} = E_{ext}$

Question 7. Which of the statements about solutions of electrolytes is not correct?

(i) Conductivity of solution depends upon size of ions.

(ii) Conductivity depends upon viscosiy of solution.

(iii) Conductivity does not depend upon solvation of ions present in solution.

(iv) Conductivity of solution increases with temperature.

Question 8. Using the data given below find out the strongest reducing agent.

$E_{Cr_2O_7^{2-}/Cr^{3+}}^{\ominus} = 1.33 \text{ V}$

$E_{Cl_2/Cl^{-}}^{\ominus} = 1.36 \text{ V}$

$E_{MnO_4^{-}/Mn^{2+}}^{\ominus} = 1.51 \text{ V}$

$E_{Cr^{3+}/Cr}^{\ominus} = – 0.74 \text{ V}$

(i) $Cl^{-}$

(ii) Cr

(iii) $Cr^{3+}$

(iv) $Mn^{2+}$

Question 9. Use the data given in Q.8 and find out which of the following is the strongest oxidising agent.

(i) $Cl^{-}$

(ii) $Mn^{2+}$

(iii) $MnO_4^{-}$

(iv) $Cr^{3+}$

Question 10. Using the data given in Q.8 find out in which option the order of reducing power is correct.

(i) $Cr^{3+} < Cl^{-} < Mn^{2+} < Cr$

(ii) $Mn^{2+} < Cl^{-} < Cr^{3+} < Cr$

(iii) $Cr^{3+} < Cl^{-} < Cr_2O_7^{2-} < MnO_4^{-}$

(iv) $Mn^{2+} < Cr^{3+} < Cl^{-} < Cr$

Question 11. Use the data given in Q.8 and find out the most stable ion in its reduced form.

(i) $Cl^{-}$

(ii) $Cr^{3+}$

(iii) Cr

(iv) $Mn^{2+}$

Question 12. Use the data of Q.8 and find out the most stable oxidised species.

(i) $Cr^{3+}$

(ii) $MnO_4^{-}$

(iii) $Cr_2O_7^{2-}$

(iv) $Mn^{2+}$

Question 13. The quantity of charge required to obtain one mole of aluminium from $Al_2O_3$ is __________.

(i) 1F

(ii) 6F

(iii) 3F

(iv) 2F

Question 14. The cell constant of a conductivity cell _____________.

(i) changes with change of electrolyte.

(ii) changes with change of concentration of electrolyte.

(iii) changes with temperature of electrolyte.

(iv) remains constant for a cell.

Question 15. While charging the lead storage battery ______________.

(i) $PbSO_4$ anode is reduced to Pb.

(ii) $PbSO_4$ cathode is reduced to Pb.

(iii) $PbSO_4$ cathode is oxidised to Pb.

(iv) $PbSO_4$ anode is oxidised to $PbO_2$.

Question 16. $\Lambda_m^0(NH_4OH)$ is equal to ______________.

(i) $\Lambda_m^0(NH_4OH) + \Lambda_m^0(NH_4Cl) - \Lambda_m^0(HCl)$

(ii) $\Lambda_m^0(NH_4Cl) + \Lambda_m^0(NaOH) - \Lambda_m^0(NaCl)$

(iii) $\Lambda_m^0(NH_4Cl) + \Lambda_m^0(NaCl) - \Lambda_m^0(NaOH)$

(iv) $\Lambda_m^0(NaOH) + \Lambda_m^0(NaCl) - \Lambda_m^0(NH_4Cl)$

Question 17. In the electrolysis of aqueous sodium chloride solution which of the half cell reaction will occur at anode?

(i) $Na^+ (aq) + e^- \rightarrow Na (s); E_{Cell}^{\ominus} = –2.71 \text{ V}$

(ii) $2H_2O (l) \rightarrow O_2 (g) + 4H^+ (aq) + 4e^–; E_{Cell}^{\ominus} = 1.23 \text{ V}$

(iii) $H^+ (aq) + e^– \rightarrow \frac{1}{2} H_2 (g); E_{Cell}^{\ominus} = 0.00 \text{ V}$

(iv) $Cl^– (aq) \rightarrow \frac{1}{2} Cl_2 (g) + e^–; E_{Cell}^{\ominus} = 1.36 \text{ V}$

Question 18. The positive value of the standard electrode potential of $Cu^{2+}/Cu$ indicates that ____________.

(i) this redox couple is a stronger reducing agent than the $H^{+}/H_2$ couple.

(ii) this redox couple is a stronger oxidising agent than $H^{+}/H_2$.

(iii) Cu can displace $H_2$ from acid.

(iv) Cu cannot displace $H_2$ from acid.

Question 19. $E_{Cell}^{\ominus}$ for some half cell reactions are given below. On the basis of these mark the correct answer.

(a) $H^+ (aq) + e^– \rightarrow \frac{1}{2} H_2 (g) ; E_{Cell}^{\ominus} = 0.00 \text{V}$

(b) $2H_2O (l) \rightarrow O_2 (g) + 4H^+ (aq) + 4e^– ; E_{Cell}^{\ominus} = 1.23 \text{V}$

(c) $2SO_4^{2–} (aq) \rightarrow S_2O_8^{2–} (aq) + 2e^– ; E_{Cell}^{\ominus} = 1.96 \text{V}$

(i) In dilute sulphuric acid solution, hydrogen will be reduced at cathode.

(ii) In concentrated sulphuric acid solution, water will be oxidised at anode.

(iii) In dilute sulphuric acid solution, water will be oxidised at anode.

(iv) In dilute sulphuric acid solution, $SO_4^{2–}$ ion will be oxidised to tetrathionate ion at anode.

Question 20. $E_{Cell}^{\ominus} = 1.1 \text{V}$ for Daniel cell. Which of the following expressions are correct description of state of equilibrium in this cell?

(i) $1.1 = K_c$

(ii) $\frac{2.303RT}{2F} \log K_c = 1.1$

(iii) $\log K_c = \frac{2.2}{0.059}$

(iv) $\log K_c = 1.1$

Question 21. Conductivity of an electrolytic solution depends on ____________.

(i) nature of electrolyte.

(ii) concentration of electrolyte.

(iii) power of AC source.

(iv) distance between the electrodes.

Question 22. $\Lambda_m^0(H_2O)$ is equal to _______________.

(i) $\Lambda_m^0(HCl) + \Lambda_m^0(NaOH) - \Lambda_m^0(NaCl)$

(ii) $\Lambda_m^0(HNO_3) + \Lambda_m^0(NaNO_3) - \Lambda_m^0(NaOH)$

(iii) $\Lambda_m^0(HNO_3) + \Lambda_m^0(NaOH) - \Lambda_m^0(NaNO_3)$

(iv) $\Lambda_m^0(NH_4OH) + \Lambda_m^0(HCl) - \Lambda_m^0(NH_4Cl)$

Question 23. What will happen during the electrolysis of aqueous solution of $CuSO_4$ by using platinum electrodes?

(i) Copper will deposit at cathode.

(ii) Copper will deposit at anode.

(iii) Oxygen will be released at anode.

(iv) Copper will dissolve at anode.

Question 24. What will happen during the electrolysis of aqueous solution of $CuSO_4$ in the presence of Cu electrodes?

(i) Copper will deposit at cathode.

(ii) Copper will dissolve at anode.

(iii) Oxygen will be released at anode.

(iv) Copper will deposit at anode.

Question 25. Conductivity k, is equal to ____________.

(i) $\frac{1}{R} \frac{l}{A}$

(ii) $\frac{G^*}{R}$

(iii) $\Lambda_m$

(iv) $\frac{l}{A}$

Question 26. Molar conductivity of ionic solution depends on __________.

(i) temperature.

(ii) distance between electrodes.

(iii) concentration of electrolytes in solution.

(iv) surface area of electrodes.

Question 27. For the given cell, $Mg|Mg^{2+}|| Cu^{2+}|Cu$

(i) Mg is cathode

(ii) Cu is cathode

(iii) The cell reaction is $Mg + Cu^{2+} \rightarrow Mg^{2+} + Cu$

(iv) Cu is the oxidising agent

Question 28. Can absolute electrode potential of an electrode be measured?

Question 29. Can $E_{Cell}^{\ominus}$ or $\Delta_rG^{\ominus}$ for cell reaction ever be equal to zero?

Question 30. Under what condition is $E_{Cell} = 0$ or $\Delta_rG = 0$?

Question 31. What does the negative sign in the expression $E_{Zn^{2+}/Zn}^{\ominus} = -0.76 \text{ V}$ mean?

Question 32. Aqueous copper sulphate solution and aqueous silver nitrate solution are electrolysed by 1 ampere current for 10 minutes in separate electrolytic cells. Will the mass of copper and silver deposited on the cathode be same or different? Explain your answer.

Question 33. Depict the galvanic cell in which the cell reaction is $Cu + 2Ag^+ \rightarrow 2Ag + Cu^{2+}$

Question 34. Value of standard electrode potential for the oxidation of $Cl^–$ ions is more positive than that of water, even then in the electrolysis of aqueous sodium chloride, why is $Cl^–$ oxidised at anode instead of water?

Question 35. What is electrode potential?

Question 36. Consider the following diagram in which an electrochemical cell is coupled to an electrolytic cell. What will be the polarity of electrodes ‘A’ and ‘B’ in the electrolytic cell?

Question 37. Why is alternating current used for measuring resistance of an electrolytic solution?

Question 38. A galvanic cell has electrical potential of 1.1V. If an opposing potential of 1.1V is applied to this cell, what will happen to the cell reaction and current flowing through the cell?

Question 39. How will the pH of brine (aq. NaCl solution) be affected when it is electrolysed?

Question 40. Unlike dry cell, the mercury cell has a constant cell potential throughout its useful life. Why?

Question 41. Solutions of two electrolytes ‘A’ and ‘B’ are diluted. The $\Lambda_m$ of ‘B’ increases 1.5 times while that of A increases 25 times. Which of the two is a strong electrolyte? Justify your answer.

Question 42. When acidulated water (dil.$H_2SO_4$ solution) is electrolysed, will the pH of the solution be affected? Justify your answer.

Question 43. In an aqueous solution how does specific conductivity of electrolytes change with addition of water?

Question 44. Which reference electrode is used to measure the electrode potential of other electrodes?

Question 45. Consider a cell given below

$Cu|Cu^{2+}|| Cl^{—}|Cl_2,Pt$

Write the reactions that occur at anode and cathode

Question 46. Write the Nernst equation for the cell reaction in the Daniel cell. How will the $E_{Cell}$ be affected when concentration of $Zn^{2+}$ ions is increased?

Question 47. What advantage do the fuel cells have over primary and secondary batteries?

Question 48. Write the cell reaction of a lead storage battery when it is discharged. How does the density of the electrolyte change when the battery is discharged?

Question 49. Why on dilution the $\Lambda_m$ of $CH_3COOH$ increases drastically, while that of $CH_3COONa$ increases gradually?

Question 50. Match the terms given in Column I with the units given in Column II.

Question 51. Match the terms given in Column I with the items given in Column II.

Question 52. Match the items of Column I and Column II.

Question 53. Match the items of Column I and Column II.

Question 54. Match the items of Column I and Column II.

Question 55. Match the items of Column I and Column II on the basis of data given below:

$E_{F_2/F^{-}}^{\ominus} = 2.87 \text{V}$, $E_{Li^+/Li}^{\ominus} = -3.5 \text{V}$, $E_{Au^{3+}/Au}^{\ominus} = 1.4 \text{V}$, $E_{Br_2/Br^{-}}^{\ominus} = 1.09 \text{V}$

Question 56. Assertion : Cu is less reactive than hydrogen.

Reason : $E_{Cu^{2+}/Cu}^{\ominus}$ is negative.

Question 57. Assertion : $E_{Cell}$ should have a positive value for the cell to function.

Reason : $E_{cathode} < E_{anode}$

Question 58. Assertion : Conductivity of all electrolytes decreases on dilution.

Reason : On dilution number of ions per unit volume decreases.

Question 59. Assertion : $\Lambda_m$ for weak electrolytes shows a sharp increase when the electrolytic solution is diluted.

Reason : For weak electrolytes degree of dissociation increases with dilution of solution.

Question 60. Assertion : Mercury cell does not give steady potential.

Reason : In the cell reaction, ions are not involved in solution.

Question 61. Assertion : Electrolysis of NaCl solution gives chlorine at anode instead of $O_2$.

Reason : Formation of oxygen at anode requires overvoltage.

Question 62. Assertion : For measuring resistance of an ionic solution an AC source is used.

Reason : Concentration of ionic solution will change if DC source is used.

Question 63. Assertion : Current stops flowing when $E_{Cell} = 0$.

Reason : Equilibrium of the cell reaction is attained.

Question 64. Assertion : $E_{Ag^{+}/Ag}$ increases with increase in concentration of $Ag^{+}$ ions.

Reason : $E_{Ag^{+}/Ag}$ has a positive value.

Question 65. Assertion : Copper sulphate can be stored in zinc vessel.

Reason : Zinc is less reactive than copper.

Question 66. Consider the Fig. 3.2 and answer the following questions.

(i) Cell ‘A’ has $E_{Cell}$ = 2V and Cell ‘B’ has $E_{Cell}$ = 1.1V which of the two cells ‘A’ or ‘B’ will act as an electrolytic cell. Which electrode reactions will occur in this cell?

(ii) If cell ‘A’ has $E_{Cell}$ = 0.5V and cell ‘B’ has $E_{Cell}$ = 1.1V then what will be the reactions at anode and cathode?

Question 67. Consider Fig. 3.2 and answer the questions (i) to (vi) given below.

(i) Redraw the diagram to show the direction of electron flow.

(ii) Is silver plate the anode or cathode?

(iii) What will happen if salt bridge is removed?

(iv) When will the cell stop functioning?

(v) How will concentration of $Zn^{2+}$ ions and $Ag^{+}$ ions be affected when the cell functions?

(vi) How will the concentration of $Zn^{2+}$ ions and $Ag^{+}$ ions be affected after the cell becomes ‘dead’?

Question 68. What is the relationship between Gibbs free energy of the cell reaction in a galvanic cell and the emf of the cell? When will the maximum work be obtained from a galvanic cell?