Engineering Chemistry S Datta

ELECTROCHEMICAL CELLS 265
41. Calculate the valency of mercurous ions with the help of the following cell:
Hg | HgNO 3
(0.001 N) in 0.1 N HNO 3
| HgNO 3
(0.01) | Hg + [Ans. 2]
42. Find the equilibrium constant of the reaction at 25°C.
2 Fe +3 + Sn +2 2 Fe +2 + Sn +4
from ∈° values given in the Table 10.2. [Ans. K = 10 21 ]
43. Calculate the equilibrium constant of the reaction at 25°C.
Fe +3 + I –
Fe +2 + 1 2 I(s)
from the ∈° (reduction) values
∈° + 2 /
⇒ 0.44 V, ∈° + 3 / ⇒ 0.036 V
Fe
Fe
∈° I( )/I
–
s
Fe
Fe
⇒ 0.5355 V. [Ans. K = 166]
44. Suggest a cell, to calculate ionic product of water. [Ans. H 2
-electrode || O 2
-electrode]
45. When calomel electrode is connected to H 2
-electrode at 18°C, gives e.m.f. value ⇒ 0.5622 V.
Calculate the pH of the solution. [Ans. 5.4]
46. E.m.f. of the cell, which is constructed by connnecting H 2
-electrode to normal calomel electrode,
at 25°C in 0.664 V. Calculate its (i) pH and (ii) H + concentration. [Ans. (i) 6.5, (ii) 3.16 × 10 –7 ]