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141. Three electrolytic cells A, B and C containing solutions of ZnSO₄(zinc sulphate), AgNO₃(silver nitrate) and CuSO₄ (copper sulphate), respectively are connected in series. A steady current of 1.5 ampere was passed through them until 1.45 g of silver is deposited at the cathode of cell B. How long did the current flow? What mass of copper and zinc were deposited? (Atomic masses: Ag = 108, Zn = 65.4, Cu = 63.5, all in amu).

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Short Answer Type

142. Calculate the standard cell potentials of galvanic cell in which the following reactions take place:
2Cr(s) + 3Cd²⁺ (aq) → 2Cr³⁺ (aq) + 3Cd
(Calculate the Δ_rG° and equilibrium constant of the reaction.)

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143. Calculate the standard cell potentials of galvanic cell in which the following reactions take place:
Fe²⁺ (aq) + Ag⁺ (aq) → Fe³⁺(aq) + Ag(s)
Calculate the Δ_rG° and equilibrium constant of the reaction.

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Long Answer Type

144. In the button cell widely used in watches and other devices the following reaction takes place:
Zn(s) + Ag₂O(s) + H₂O(l) → Zn²⁺(aq) + 2Ag(s) + 2OH^– (aq)
Determine Δ_rG° and E° for the reaction.

The formula of standard cell potential is

E^o_cell = E^o_right – E^o_left

E^o_cell = 0.344 – ( – 0.76)

E^o_cell = 0.344+0.076 V

E^o_cell = +1.104 V

In balanced reaction there are 2 electron are transferring so that n = 2

Faraday constant, F = 96500 C mol⁻¹

E^o_cell = + 1.104 V

Use formula

∆_rG^θ = – nFE^o_cell

Plug the value we get

Then, = −2 × 96500 C mol⁻¹ × 1.104 V

= −212304 CV mol⁻¹

= −212304J mol⁻¹

= −212.304kJ mol⁻¹

= −213.04 kJ

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Short Answer Type

145. The resistance of a conductivity cell containing 0.001 M KCl solution at 298 K is 1500Ω. What is the cell constant if conductivity of 0.001 M KCl solution at 298 K is 0.146 x 10^–3 s cm^–1.

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Long Answer Type

146. Conductivity of 0.00241 M acetic acid solution is 7.896 x 10^–5 S cm^-1. Calculate its molar conductivity in this solution. If Λ°_m for acetic acid be 390.5 S cm² mol^–1, what would be its dissociation constant?

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Short Answer Type

147. Calculate the emf of the cell Zn/Zn²⁺(0.1 M) || Cd²⁺ (0.01 M) | Cd at 298 k. (given)
E°_Zn²⁺/Zn = – 0.76 V and E°_Cd²⁺/Cd = – 0.40 V).

1204 Views

Long Answer Type

148.

Cu²⁺ + 2e^– → Cu E° = + 0.34 V
Ag⁺ + 1e^– → Ag E° = + 0.80 V
(i) Construct a galvanic cell using the above data.
(ii) For what concentration of Ag⁺ ions will the emf of the cell be zero at 25°C, if the concentration of Cu²⁺ is 0.01 M ? [log 3.919 = 0.593]

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149. Silver is electrodeposited on a metallic vessel of total surface area 900 cm² by passing a current of 0.5 amp for two hours. Calculate the thickness of silver deposited. [Given : Density of silver = 10.5 g cm^–3, Atomic mass of silver = 108 amu, F = 96,500 C mol^–1]

603 Views

Short Answer Type

150. Calculate the number of coulombs required for the oxidation of 1 mole of water to oxygen as per equation:
2H₂O → 4H⁺ + O₂ + 4e^–
[Given: 1 F = 96,500 C mol^–1]

190 Views