At 25C, the molar conductance of 0.007 M hydrofluoric acid is 150

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 Multiple Choice QuestionsMultiple Choice Questions

41.

The two half-cell reactions of an electrochemical cell is given as

Ag+ + e-  Ag;                   E°Ag+/Ag=-0.3995 V        Fe2+ Fe3+ + e- ;     E°Fe3+ /Fe2+= -0.7120 V 

The value of cell EMF will be

  • -0.3125 V

  • 0.3125 V

  • 1.114 V

  • -1.114V


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42.

At 25C, the molar conductance of 0.007 M hydrofluoric acid is 150 mho cm2mol-1and its λ°m = 500 mho cm2mol-1. The value of the dissociation constant of the acid at the given concentration at 25°C is

  • 7 X 10-4 M

  • 7 X 10-5 M

  • 9 X 10-3 M

  • 9 X 10-4 M


D.

9 X 10-4 M

 Degree of dissociation, α =λ°cλ°m= 150500= 0.3Given, C = 0.007 M Hydrofluoric acid dissociates in the following mannerHF       H+ +    F-C              0         0    initially C-               at time tDissociation constant, Ka= [H+] [F-][HF]=·C( 1-α)= 2(1-α)On substituting values, we get Ka= 0.007 × (0.3)2(1-0.3)= 63 ×10-3×10-20.7      =  9×10-4 M


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43.

The formal potential of Fe3+ /Fe4+ in a sulphuric acid and phosphoric acid mixture (E° = + 0.61 V) is much lower than the standard potential (E° = + 0. 77 V). This is due to

  • formation of the species [FeHPO4]+

  • lowering of potential upon complexation

  • formation of the species [FeSO4]+

  • high acidity of the medium


44.

A conductivity cell has been calibrated with a 0.01 M 1 : 1 electrolyte solution (specific conductance, k = 1.25 × 10-3S cm-1) in the cell and the measured resistance was 800 Ω at 25°C. The cell constant will be

  • 1.02 cm-1

  • 0.102 cm-1

  • 1.00 cm-1

  • 0.5 cm-1


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45.

Equivalent conductivity at infinite dilution for sodium-potassium oxalate [(COO-)2 Na+K+] will be [given molar conductivities of oxalate, K+ and Na+ ions at infinite dilution are 148.2, 50.1, 73.5 S cm mol' respectively]

  • 271.8 S cm2 eq-1

  • 67.95 S cm2 eq-1

  • 543.6 S cm2 eq-1

  • 135.9 S cm2 eq-1


46.

The standard reduction potential E° for half-reaction are

Zn → Zn2+ + 2e- ; E° = + 0.76 V

 Fe → Fe2+ + 2e- ; E° = + 0.41 V

The EMF of the cell reaction

Fe2+ + Zn → Zn2+ + Fe is

  • -0.35 V

  • +0.35 V

  • +1.17 V

  • -1.17 V


47.

On passing 'C ampere of current for time 't' sec through 1 L of 2 (M) CuSO4 solution (atomic weight of Cu= 63. 5), the amount 'm' of Cu (in gram) deposited on cathode will be

  • m = Ct / (63.5 x 96500)

  • m = Ct / (31.25 x 96500)

  • m = (C x 96500) / (31.25xt)

  • m = (31.25 X C x t) / 96500


48.

When 96.5 C of electricity is passed through a solution of silver nitrate (at wt. of Ag = 107. 8 7 which is approx. 108), the amount of silver deposted is

  • 5.8 mg

  • 10.8 mg

  • 15.8 mg

  • 20.8 mg


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49.

The standard reduction potentials at 298 K for the following half reactions are given against each

                          Zn2+(aq) + 2e-  Zn(s) -0.762 VCr3+(aq) + 2e-  Cr(s) - 0.740 V2H+(aq) + 2e-  H2(s)  0.000 VFe3+(aq) + 2e-  Fe2+(aq) 0.770 V

Which is the strongest reducing agent ?

  • Zn(s)

  • Cr(s)

  • H2(s)

  • Fe2+ (aq)


50.

On passing 3A of electricity for 50 min, 1.8 g metal is deposited, the equivalent mass of metal is

  • 9.3

  • 19.3

  • 38.3

  • 39.9


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