ELECTROCHEMISTRY QUIZ-6

Q1. 

•  -36.24
•  -19.65
•  -31.54
•  -48.25

Solution

Q2.The standard electrode potentials of Ag^+ / Ag is +0.80 V and Cu^+ /Cu is +0.34 V. These electrodes are connected through Asalt bridge and if

•  Copper electrode acts as Acathode then E_cell^° is +0.46 V
•  Copper electrode acts as anode then E_cell^° is +0.46 V
•  Silver electrode acts as anode then E_cell^° is -0.34 V
•  Silver electrode acts as Acathode then E_cell^° is -0.34 V

Solution

Q3.  KCl(aq) cannot be used as a salt bridge for the cell Cu(s)|CuSO_4 (aq)|| AgNO_3 (aq)|Ag(s) because :

•   CuCl_2 is precipitated
•  All of these
•  Cl_2 gas is given out
•  AgCl is precipitated

Solution
AgNO_3+KCl ⟶AgCl ↓ + KNO_3.

Q4. Quantity of charge is measured in :

•  amphere^(-1) sec.
•  ampere 〖sec^(-1).〗⁡
•  ampere
•  ampere-sec.

Solution
Quantity of current is charge, i.e., coulomb or ampere sec.

Q5.The standard reduction potentials at 298 K for the following half-cell reactions are given Zn^(2+) (aq) + 〖2e〗^- ⇌ Zn (s); -0.762 V Cr^(3+) (aq) + 〖3e〗^- ⇌ Cr (s); -0.74 V 〖2H〗^+ (aq)+ 〖2e〗^- ⇌ H_2 (g); +0.00 V Fe^(3+) (aq)+ e^- ⇌ Fe^(2+) (aq); +0.77 V Which one of the following is the strongest reducing agent?

•  Zn (s)
•  Cr(s)
•  H_2 (s)
•  Fe^(2+) (aq)

Solution
 The metals having higher negative value of standard reduction potential are placed above hydrogen in electrochemical series. The metals places above hydrogen has a great tendency to donate electrons or oxidising power. The metals having great oxidizing power are strongest reducing agent. Zn has higher negative value of standard reduction potential. Therefore, it is the strongest reducing agent.

Q6. The standard reduction potential E^° for half reactions are Zn = Zn^(2+) + Ze E^° = + 0.76 V Fe = Fe^(2+) + Ze E^° = + 0.41 V The emf of the cell reaction Fe^(2+) + Zn = Zn^(2+) + Fe is

•  - 0.35 V
•  +0.35
• +1.17 V
•  -1.`17 V

Solution

Q7.The atomic weight of Al is 27. When a current of 5 faraday is passed through a solution of Al^(3+) ions, the wt.of Al deposited is :

•  27 g
•  36 g
•  45 g
•  9 g

Solution
Eq. of Al deposited = 5 ∴ wt. of Al = 5×27/3=45 g .

Q8.The electroplating with chromium is undertaken because :

•  Of high reactivity of chromium metal
•  Chromium gives a protective and decorative coating to the base metal
•  Chromium can form alloys with other metals
•  Electrolysis of chromium is easier

Solution
A thin film of Cr_2 O_3 is formed on Cr Surface

Q9.The standard reduction potential at 290 K for the following half reactions are, (i) Zn^(2+) +2e ⟶Zn(s); E°= -0.762 V (ii) Cr^(3+) +3e ⟶Cr(s); E°= -0.740 V (iii)2H^+ +2e ⟶H_2 (g); E°= -0.000 V (iv) Fe^(3+) + e ⟶Fe^(2+); E°= +0.77 V Which is the strongest reducing agent?

•  H_2
•  Fe^(2+)
•  Cr
•  Zn

Solution
Zn has more +ve E_OP^° and thus possesses more tendency to get oxidise and act as reducing agent

Q10. Consider the reaction, M^(n+) (aq)+ne ⟶M^0 (s). The standard reduction potential values of the metals M_1,M_2 and M_3 are -0.34 V,-3.05 V and -1.66 V respectively. The order of their reducing power will be :

•  M_1>M_3>M_2
•  M_2>M_3>M_1
•  M_3>M_2>M_1
• M_1>M_2>M_3

Solution
More is E_OP^°, more is reducing power of metal.