Electrochemistry-NCERT Exemplar Problems & Solution

MCQs Type-I

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

(i) Pt (s) |H₂ (g,0.1 bar)| H⁺ (aq.,1 M)|| Cu²⁺(aq.,1M)| Cu

(ii) Pt(s) |H₂ (g, 1 bar)| H⁺ (aq.,1 M) ||Cu²⁺ (aq.,2 M)| Cu

(iii) Pt(s) |H₂ (g, 1 bar)| H⁺ (aq.,1 M)|| Cu²⁺ (aq.,1 M)| Cu

(iv) Pt(s) |H₂ (g, 1 bar)| H⁺ (aq.,0.1 M)|| Cu²⁺ (aq.,1 M) | Cu

Answer:

(iii) Pt(s) |H₂ (g, 1 bar)| H⁺ (aq.,1 M)|| Cu²⁺ (aq.,1 M)| Cu

Question: 2. Electrode potential for Mg electrode varies according to the equation

`E_(mg^(2+)|Mg )= E_(Mg^(2+)|Mg)^(⊖) – (0.059)/2 log1/([Mg^(2+)])`

The graph of `E_(Mg^(2+)|Mg)` vs `log[Mg^(2+)]` isv

(i)

(ii)

(iii)

(iv)

Answer: (ii)

Question: 3. Which of the following statement is correct?

(i) E_Cell and `Delta r G` of cell reaction both are extensive properties.

(ii) E_Cell and `Delta r G` 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.

Answer:

(iii) E_Cell is an intensive property while `Delta rG` of cell reaction is an extensive 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

Answer: (ii) Cell emf

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.

Answer: (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

Answer: (iii) E_ext > E_cell

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.

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

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

`E_(Cr_2O_7^(2-)//Cr^(3+))^(⊖)=1.33V`

`E_(Cl_2//Cl^-)^(⊖) =1.36V`

`E_(MnO_4^-//Mn^(2+))^(⊖)=1.51V`

`E_(Cr^(3+)//Cr)^ (⊖) = -0.74V`

(i) `Cl^-`

(ii) `Cr`

(iii) `Cr^(3+)`

(iv) `Mn^(2+)`

Answer: (ii) `Cr`

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+)`

Answer: (iii) `MnO_4^-`

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`

Answer: (ii) `Mn^(2+)\ <\ Cl^– \<\ Cr^(3+)\ <\ 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+)`

Answer: (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+)`

Answer: (i) `Cr^(3+)`

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`

Answer: (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.

Answer: (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`.

Answer: (i) `PbSO_4` anode is reduced to `Pb`.

Question: 16. `Lamda_(m(NH_4OH))^0` is equal to ___________.

(i) `Lamda_(m(NH_4OH))^0` `+Lamda_(m(NH_4Cl))^0` `-Lamda_((HCl))^0`

(ii) `Lamda_(m(NH_4Cl))^0` `+Lamda_(m(NaOH))^0` `-Lamda_((NaCl))^0`

(iii) `Lamda_(m(NH_4Cl))^0` `+Lamda_(m(NaCl))^0` `-Lamda_((NaOH))^0`

(iv) `Lamda_(m(NaOH))^0` `+Lamda_(m(NaCl))^0` `-Lamda_((NH_4Cl))^0`

Answer: (ii) `Lamda_(m(NH_4Cl))^0` `+Lamda_(m(NaOH))^0` `-Lamda_((NaCl))^0`

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

(i) `Na^+ (aq) + e^- -> Na (s); E_(Cell)^ (⊖)= –2.71V`

(ii) `2H_2O (l) -> O_2 (g) + 4H^+(aq)+4e^-; E_(Cell)^ (⊖)= 1.23 V`

(iii) `H^+(aq) + e^- -> 1/2H_2(g); E_(Cell)^ (⊖)= 0.00V`

(iv) `Cl^-(aq) ->1/2Cl_2(g)+e^-; E_(Cell)^ (⊖)= 1.36V`

Answer: (iv) `Cl^-(aq) ->1/2Cl_2(g)+e^-; E_(Cell)^ (⊖)= 1.36V`

II. Multiple Choice Questions (Type-II)

Note : In the following questions two or more than two options may be correct.

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.

Answer:

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

And

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

Question: 19. `E_(Cell)^ (⊖)` for some half cell reactions are given below. On the basis of these mark the correct answer.

(a) `H^+ (aq) + e^- ->1/2H_2(g)`; `E_(Cell)^ (⊖)=0.00V`

(b) `2H_2O (l)-> O_2 (g) + 4H^+ (aq) + 4e^–` ; `E_(Cell)^ (⊖)=1.23V`

(c) `2SO_4(aq) -> S_2O_8^(2-)(aq)+2e-` ; `E_(Cell)^ (⊖)=1.96V`

(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.

Answer:

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

And

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

Question: 20. `E_(Cell)^ (⊖) = 1.1V` for Daniel cell. Which of the following expressions are correct description of state of equilibrium in this cell?

(i) `1.1 = K_c`

(ii) `(2.303RT)/(2F)logK_c=1.1`

(iii) `log K_c = (2.2)/(0.059)`

(iv) `log K_c = 1.1`

Answer:

(ii) `(2.303RT)/(2F)logK_c=1.1`

And

(iii) `log K_c = (2.2)/(0.059)`

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.

Answer:

(i) nature of electrolyte.

And

(ii) concentration of electrolyte.

Question: 22. `Lamda_m^0H_2O` is equal to _________.

(i) `Lamda_(m(HCl))^0 + Lamda_(m(NaOH))^0 – Lamda_(m(NaCl))^0`

(ii) `Lamda_(m(HNO_3))^0 + Lamda_(m(NaNO_3))^0 – Lamda_(m(NaOH))^0`

(iii) `Lamda_(m(HNO_3))^0 + Lamda_(m(NaOH))^0 – Lamda_(m(NaNO_3))^0`

(iv) `Lamda_(m(NH_4OH))^0 + Lamda_(m(HCl))^0 – Lamda_(m(NH_4Cl))^0`

Answer:

(i) `Lamda_(m(HCl))^0 + Lamda_(m(NaOH))^0 – Lamda_(m(NaCl))^0`

And

(iii) `Lamda_(m(HNO_3))^0 + Lamda_(m(NaOH))^0 – Lamda_(m(NaNO_3))^0`

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.

Answer:

(i) Copper will deposit at cathode.

And

(iii) Oxygen will be released 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.

Answer:

(i) Copper will deposit at cathode.

And

(ii) Copper will dissolve at anode.

Question: 25. Conductivity `k` , is equal to ____________.

(i) `(1l)/(RA)`

(ii) `(G**)/R`

(iii) `Lamda_m`

(iv) `l/A`

Answer:

(i) `(1l)/(RA)`

And

(ii) `(G**)/R`

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.

Answer:

(i) temperature.

And

(iii) concentration of electrolytes in solution.

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+)-> Mg^(2+) + Cu`

(iv) `Cu` is the oxidising agent

Answer:

(ii) Cu is cathode

And

(iii) The cell reaction is `Mg + Cu^(2+)-> Mg^(2+) + Cu`

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