Q25 of 46 Page 1

E° for the given redox reaction is 2.71 V


Calculate Ecell for the reaction. Write the direction of flow of current when an external opposite potential applied is


(i) Less than 2.71 V and


(ii) Greater than 2.71 V


OR


(a) A steady current of 2 A was passed through two electrolytic cells X and Y connected in series containing electrolytes FeSO4 and FeSO4 until 2.8 g of Fe deposited at the cathode of cell X. how long did the current flow? Calculate the mass of Zn deposited at the cathode of cell Y.


(b) In the plot of molar conductivity (Λm) v/s square root of concentration (c1/2), following curve is obtained for two electrolytes A and B:



Answer the following:


(i) Predict the nature of electrolytes A and B


(ii) What happens on extrapolation of Λm to concentration approaching zero for electrolytes A and B?


Given:


E° = 2.71 V


Solution:



For the given reaction the Nernst equation is written as,






For the given conditions,


(i) Ecell > 2.71 V, the current flows from cathode to anode (conventional direction)


(ii) Ecell < 2.71 V, i.e. the external voltage is greater than the emf of the cell, the direction of the flow is from anode to cathode (direction is reversed)


OR


(i) As the conductivity is linearly dependent on the square root of concentration the line on Λ v/s c1/2 suggests that A is a strong electrolyte.


When initially when the concentration is increases the conductivity drops rapidly but after certain point there are enough ions and no more addition of B will decrease the conductivity significantly, thus B is a weak electrolyte.


(ii) Extrapolation of values of Λm gives the maximum values of conductivity i.e. Λ°m for strong electrolytes at zero concentration. This cannot be found for Weak electrolytes as the relation is non-linear curvature which does not meet the conductivity.


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23

Complete the following reactions:

(i)


(ii)


(iii)


OR


Write the chemical equations for the following reactions:


(i) Propanone is treated with dilute Ba(OH)2.


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(iii) Benzoyl chloride is hydrogenated in presence of Pd/BaSO4


 24

Differentiate between the following:

(i) Amylose and amylopectin


(ii) Peptide linkage and glycosidic linkage


(iii) Fibrous proteins and globular proteins


OR


Write the chemical reactions to show that open structure of D-glucose contains the following:


(i) Straight chain


(ii) Five alcohol groups


(iii) Aldehyde as carbonyl group


 26

(a) How do you convert the following:

(i) Phenol to anisole


(ii) Ethanol to propan-2-ol


(b) write the mechanism of the following reaction:



(c) Why phenol undergoes electrophilic substitution more easily than benzene?


OR


(a) Account for the following:


(i) O-nitrophenol is more steam volatile than p-nitrophenol


(ii) T-butyl chloride on heating with sodium methoxide gives 2-methylpropene instead of t-butylmethylether.


(b) Write the reaction involved in the following:


(i) Reamer-Tiemann reaction


(ii) Friedel-Crafts alkylation of phenol


(c) Give simple chemical test to distinguish between ethanol and phenol.


 27

(a) Give reasons for the following:

(i) Sulphur in vapour state shows paramagnetic behaviour


(ii) N-N bond us weaker than P-P bond


(iii) Ozone is thermodynamically less stable than oxygen.


(b) Write the name of gas released when Cu is added to


(i) Dilute HNO3


(ii) Conc. HNO3


OR


(a) Answer the following:


(i) Write the disproportionation reaction of H3PO3


(ii) Draw the structure of XeF4


(b) Account for the following:


(i) Although fluorine has less negative electron gain enthalpy yet F2 is strong oxidising agent.


(ii) Acidic character decreases from N2O3 to Bi2O3


(c) Write a chemical reaction to test sulphur dioxide gas. Write chemical equation involved.