Q24 of 26 Page 1

(a) Calculate ∆G° and log Kc for the following reaction at 298 K:

2Cr(s) + 3Fe2+(aq) → 2Cr3+(aq) + 3Fe(s)


Given: E°cell = 0.30 V


(b) Using the E° values of A and B, predict which is better for coating the surface of iron [E° (Fe2+|Fe) = –0.44 V] to prevent corrosion and why?


Given: E°(A2+|A) = –2.37 V : E°(B2+|B) = –0.14 V


OR


(a) The conductivity of 0.001 mol/L solution of CH3COOH is 3.905 × 10-5 S/cm. Calculate its molar conductivity and degree of dissociation.


Given: λ° (H+) = 349.6 S cm2 mol-1 and λ° (CH3COO-) = 40.9 S cm2 mol-1.


(b) What type of battery is lead storage battery? Write the overall reaction occurring in lead storage battery.


(a) Given:


2Cr(s) + 3Fe2+(aq) → 2Cr3+(aq) + 3Fe(s)


E°cell = 0.30 V


T = 298 K



And n (no. of electrons) = 6


Substituting the values in ΔG° = -nFE°cell


ΔG° = - 6 96500 0.30


= -173700 J/mol


= -173.7 KJ/mol


Now, log Kc =


log Kc =


= 30.50


(b) We have to coat the surface of iron having E° (Fe2+|Fe) = –0.44 V to prevent corrosion. Corrosion is the phenomenon of oxidation of iron, if we will coat the surface of iron with a substance having higher oxidation potential than that of iron, then that substance will be oxidized instead of iron. Thus, substance A will be coated on iron.


Oxidation potential of Fe: 0.44


Oxidation potential of A: 2.37


Oxidation potential of B: 0.14


OR


(a) Given, K, conductivity of CH3COOH = 3.905 10-5 Scm-1,


Molarity of CH3COOH, M = 0.001 M,


(H+) = 349.6 Scm2mol-1 and


⋀°(HCOO-) =40.9 Scm2mol-1


Molar conductance, ⋀m = Scm2mol-1


⋀m = = 39.05 Scm2mol-1


According to Kohlrauch’s Law, limiting molar conductivity of an electrolyte can be represented as sum of individual contribution of cation and anion of electrolyte.


Therefore, limiting molar conductivity of HCOOH can be written as,


⋀°m (CH3COOH) = ⋀°m (CH3COO-) + ⋀°m (H+)


= 40.9 Scm2mol-1 + 349.6 Scm2mol-1


= 390.5 Scm2mol-1


Degree of dissociation,


= 0.1


Molar conductivity and degree of dissociation of ethanoic acid is 39.05 Scm2mol-1 and 0.1 respectively.


(b) Lead storage battery is a secondary battery. The overall reaction occurring in lead storage battery is


Pb + PbO2 + 2H2SO4 → 2PbSO4 + 2H2O


More from this chapter

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22

Write the major product(s) in the following reactions:


 23

Due to hectic and busy schedule, Mr. Awasthi made his life full of tensions and anxiety. He started taking sleeping pills to overcome the depression without consulting the doctor. Mr. Roy, a close friend of Mr. Awasthi, advised him to stop taking sleeping pills and suggested to change his lifestyle by doing Yoga, meditation and some physical exercise. Mr. Awasthi followed his friend’s advice and after few days he started feeling better.

After reading the above passage, answer the following:


(i) What are the values (at least two) displayed by Mr. Roy?


(ii) Why it is not advisable to take sleeping pills without consulting doctor?


(iii) What are tranquilizers? Give two examples.


 25

(a) Account for the following:

(i) Mn2O7 is acidic whereas MnO is basic.


(ii) Though copper has completely filled d-orbital (d10) yet it is considered as a transition metal.


(iii) Actinoids show wide range of oxidation states.


(b) Write the preparation of potassium permanganate from pyrolusite ore (MnO2).


OR


(a) The elements of 3d transition series are given as:



Answer the following:


(i) Which element has the highest m.p. and why?


(ii) Which element is a strong oxidizing agent in +3 oxidation state and why?


(iii) Which element is soft and why?


(b) Write the equations involved in the preparation of Potassium dichromate from Sodium chromate (Na2CrO4).


 26

(a) Write the major product(s) in each of the following reactions:


(b) Write the chemical reaction involved in the following reactions:


(i) Kolbe’s reaction


(ii) Friedal-Crafts acetylation of anisole


OR


(a) What happens when


(i) Phenol reacts with Bromine water?


(ii) Ethanol reacts with CH3COCl/pyridine?


(iii) Anisole reacts with HI?


Write the chemical equations involved in the above reactions.


(b) Distinguish between:


(i) Ethanol and phenol


(ii) Propan-2-ol and 2-methylpropan-2-ol