# MCQ | Electrochemistry

Practice Test – I

Q:1. Which  are true for a standard hydrogen electrode

(A) The hydrogen ion concentration is 1 M

(B) Temperature is 25°C.

(C) Pressure of hydrogen is 1 atmosphere.

(D) It contains a metallic conductor which does not adsorb hydrogen.

Ans: (A) , (B) (C)

Q:2. For the cell Tl | Tl+ (.001 M) || Cu2+ (.1M) | Cu. ECell at 25°C is. 83V which can be increased

(A) by increasing [Cu2+]

(B) by increasing [TI+]

(C) by decreasing [Cu2+]

(D) by decreasing [TI+]

Ans: (A) , (D)

Q:3.Which represents disproportionation

(A) 2Cu+  → Cu+2 + Cu

(B) 3I2  → 5I + I +5

(C) Cu+2 + Zn  → Zn+2 +  Cu

(D) None

Ans: (A) , (B)

Q:4.The standard potentials at 25 °C for the following half reactions are given against then

Zn2+ + 2e → Zn, E0 = –0.762 V

Mg2+ + 2e → Mg, E0 = 2.37 V

When zinc dust is added to a solution of magnesium chloride

(A) No reaction will take place

(B) Zinc chloride is formed

(C) Zinc dissolve in solution

(D) Magnesium is precipitated

Ans: (A)

Q:5.Emf of the cell
Ni | Ni2+ (0.1 M) || Au3+ (1.0 M) | Au will be

$E^o_{Ni/Ni^{2+}} = 0.25$ , $E^o_{Au/Au^{3+}} = 1.5 V$

(A) 1.75 V

(B) + 1.7795 V

(C) + 0.7795 V

(D) – 1.7795 V

Ans: (B)

Q:6.The quantity of electricity needed to electrolyse completely 1 M solution of
CuSO­4, Bi2(SO4)3, AlCl3 and AgNO3 each will be

(A) 2F, 6F, 3F, and 1F respectively

(B) 6F, 2F, 3F and 1F respectively

(C) 2F, 6F, 1F and 3F respectively

(D) 6F, 2F, 1F and 3F respectively

Ans: (A)

Q:7. If the pressure of H2 gas is increased from 1 atm to 100 atm. Keeping H+ concentration constant at 1 M, the voltage of Hydrogen half cell at 25° C will be

(A) 0.059 V

(B) 0.59 V

(C) 0.0295 V

(D) 0.118 V

Ans: (A)

Q:8. If aqueous solutions of AgNO3 is electrolysed using inert electrode the gas evolved at anode is

(A) NO2

(B) O2

(B) H2

(D) N2O

Ans: (B)

Q:9. The standard cell potential for the electrochemical cell

Ag/Ag+ || AgI/Ag ;     $E^o_{I^-/Agl(s)/Ag } = -0.151 V \; , E^o_{Ag^+/Ag} = 0.799 V$

(A) + 0.950 V

(B) – 0.950 V

(C) – 0.648 V

(D) + 0.648 V

Ans: (B)

Q:10. If equal quantities of electricity are passed through three voltmeter containing FeSO4, Fe2(SO4)3 and Fe(NO3)3 then

(A) The amount of iron deposited in FeSO4  and Fe2(SO4)3 is equal

(B) The amount of iron deposited in Fe(NO3)3 is 2/3 of the amount of iron deposited in FeSO4

(C) The amount of iron deposited is Fe2(SO4)3 and Fe(NO3)3 is equal

(d) Same gas will evolve in all three cases at anode.

Ans: (B) ,(C) , (D)

Q:11. Two platinum electrodes are dipped in a solution of HCl, and H2 & Cl2 gases are made to bubble through them at constant pressure. One half cell is
Pt, H2(g)|H3O+ (aq) with reaction ½ H2 + H2O → H3O+ + e.

The electrode at which this half cell reaction would occur is

(A) Cathode

(B) Anode

(C) May be anode or cathode

(D) Neither anode nor cathode

Ans: (B)

Q:12. A Chemist found that the standard electrode potential $E^o_{Zn^{+2}/Zn}$, of the zinc electrode is –0.763 Volt. Which cell will give this value of EMF.

(A) Pt, H2 (1 atm) | H+ (10M) || Zn+2 (10M) | Zn

(B) Pt, H2 (1 atm) | H+ (1M) || Zn+2 (1M) | Zn

(C) Zn | Zn+2 (1M) || H+ (1M) | H2 (1 atm), Pt

(D) Zn | Zn+2 (10M) || H+ (10M) | H2 (1 atm), Pt

Ans: (C)

Q:13. At the reduction-electrode, this reaction takes place

$A^{+Z} + Z e^- \rightleftharpoons A$

Which is/are correct relation(s) for electrode potential?

(A) $E = E^o + \frac{R T}{Z F} ln \frac{[A]}{[A^{+z}]}$

(B) $E = E^o – \frac{R T}{Z F} ln \frac{[A]}{[A^{+z}]}$

(C) $E = E^o + \frac{R T}{F} ln \frac{[A^{+z}]}{[A]}$

(D) $E = E^o – \frac{R T}{F} ln \frac{[A^{+z}]}{[A]}$

Ans: (B)

Q:14. Which of the following is/are function(s) of salt bridge.

(A) It completes the electric circuit with electrons flowing from one electrode to other through external wires and a flow of ions between the two compartments through salt bridge.

(B) It prevents the accumulation of the ions

(C) Both (A) and (B) are correct

(D) None of these

Ans: (C)

Q:15. Given:
$Fe^{+2} + 2e^– \rightleftharpoons Fe \; E^o = -0.44 V$

$Co^{+2} + 2e^– \rightleftharpoons Co \; E^o = -0.28 V$

$Ca^{+2} + 2e^– \rightleftharpoons Ca \; E^o = -2.87 V$

$Cu^{+2} + 2e^– \rightleftharpoons Cu \; E^o = + 0.337 V$

Which is the most electropositive metal ?

(A) Fe

(B) Co

(C) Ca

(D) Cu

Ans: (C)

Q:16. Which of the following graphs will correctly correlate Ecell as a function of concentrations for the cell (for different M and M’)

Zn(s) + Cu+2(M) → Zn+2(M’) + Cu(s),  = 1.10 V

$\large X-axis : log\frac{[Zn^{+2}]}{[Cu^{+2}]}$ , Y-axis: Ecell Ans: (B)

Q:17. The amount of ion discharged during electrolysis is directly proportional to :

(A) Resistance

(B) Time

(C) Current

(D) Chemical equivalent of the ion

Ans: (B), (C), (D)

Q:18. The reaction Cu+2 (aq) + 2Cl(aq) → Cu(s) + Cl2(g) has Ecell o = -1.02 V. This reaction

(A)can be made to produce electricity in a voltaic cell

(B)can be made to occur in an electrolytic cell

(C)occurs whenever Cu+2 and Cl are brought together in aqueous solution.

(D)can occur in acidic solution but not in basic solution.

Ans: (B)

Q:19. Cu+ + e ® Cu, E0 = x1 V, Cu+2 + 2e  →Cu, E0 = x2 V

For Cu+2 + e ® Cu+, E0 will be

(A) x1  – 2 x

(B) x1  + 2 x2

(C) x1  – x2

(D) 2x2  – x1

Ans: (D)

Q:20. Apollo-II was the spacecraft used by American astronauts during the moon explorations in 1969. Which of the following do you think would be best source of energy for the space craft ?

(A) Dry cell

(C) Fuel cell

(D) Alkaline battery