Q25 of 26 Page 1

(a) Write the cell reaction and calculate the e.m.f. of the following cell at 298 K.

Sn (s ) | Sn 2+ (0.004 M )|| H+(0.020 M ) | H 2 (g )(1bar)| Pt (s)


(Given: E0 Sn+2/Sn=-0.14V )


(b) Give reasons:


(i) On the basis of E0 values, O2 gas should be liberated at anode, but it is Cl2 gas which is liberated in the electrolysis of aqueous NaCl.


(ii) The conductivity of CH3COOH decreases on dilution.


OR


(a) For the reaction


2AgCl(s) + H2(g) (1 atm) → 2Ag(s) + 2H+ + 2H+ (0.1M) + 2Cl- (0.1M),


ΔG° = -43600J at 35° C.


Calculate the e.m.f. of the cell.


[log 10-n = -n]
(b) Define fuel cell and write its two advantages.

(a) The Half cell reaction can be written as:



= -0.11× (log 0.004) V=0.26 V



Ecell= 0.0+ 0.0592 × (log H+)


E cell= 0.0591 × (-1.7)


Ecell= - 0.10 V


(b) (i) The standard reduction potential of water is slightly less, and therefore it has slightly more chance of getting oxidised. However, in concentrated solution of NaCl, oxidation of chloride ions is preferred than water at the anode. The unexpected result is due higher voltage required for electrolysis due to over voltage.


The reaction at the anode:



(ii) The number of ions furnished by an electrolyte depends upon the degree of dissociation with an increase in dilution the degree of dissociation increases. As a result molar conduction of acetic and increases with dilution.


OR


(a) ΔG 0 = -43600 J at 25oC.


Calculate the e.m.f. of the cell.


[log 10–n = – n]




According to the Nernst equation:




Ecell =-0.45-(0.059) log(0.1× 0.1)


=-0.51× log(10-2)=-0.51× (-2)=1.02 V


Ecell=1.02V


(b) These are voltaic cells in which the reactants are continuously supplied to the electrodes. There are


designed to convert the energy from the combustion of fuel directly into electrical energy.


Advantage : -


(1) A fuel cell works with an efficiency of 70 %


(2) These are no objectionable by-products and therefore, its a pollution free source of energy.


More from this chapter

All 26 →
22

(a) Write the formula of the following coordination compound : Iron(III) hexacyanoferrate (II)

(b) What type of isomerism is exhibited by the complex


(c) Write the hybridisation and number of unpaired electrons in the complex [CoF6 ]3- . (Atomic No. of Co = 27)

 23

Shyam went to a grocery shop to purchase some food items. The shopkeeper packed all the items in polythene bags and gave them to Shyam. But Shyam refused to accept the polythene bags and asked the shopkeeper to pack the items in paper bags. He informed the shopkeeper about the heavy penalty imposed by the government for using polythene bags. The shopkeeper promised that he would use paper bags in future in place of polythene bags.

Answer the following :


(a) Write the values (at least two) shown by Shyam.


(b) Write one structural difference between low-density polyethene and high-density polyethene.


(c) Why did Shyam refuse to accept the items in polythene bags ?


(d) What is a biodegradable polymer? Give one example?

 24

(a) Give reasons:


(i) H3PO3 undergoes disproportionation reaction, but H3PO4 does not.


(ii) When Cl2 reacts with an excess of F2. ClF3 is formed and not FCl3.


(iii) Dioxygen is a gas while Sulphur is a solid at room temperature.


(b) Draw the structures of the following:


(i) XeF4


(ii) HCLO3


OR


(a) When concentrated sulphuric acid was added to n unknown salt present in a test tube a brown gas(A) was evolved. This gas intensified when copper turning were added to this test tube . On cooling, the gas (A) changed int a colourless solid(B).


(i) Identify (A) and (B).


(ii) Write the structures of (A) and (B).


(iii) Why does gas (A) change to solid on cooling?


(b) Arrange the following in the decreasing order of theirreducing character:


HF, HCl, HBr, HI


(c) Complete the following reaction:


XeF4 +SbF5→

 26

(a) Write the reactions involved in the following :

(i) Hofmann bromamide degradation reaction


(ii) Diazotisation


(iii) Gabriel phthalamide synthesis


(b) Give reasons :


(i) (CH3)2NH is more basic than (CH3)3N in an aqueous solution.


(ii) Aromatic diazonium salts are more stable than aliphatic diazonium salts.


OR


(a) Write the structures of the main products of the following reactions:



(b) Give a simple chemical test to distinguish between Aniline and N,N-dimethylaniline.


(c) Arrange the following in the increasing order of their pKb value:


C6H5NH2, C2H5NH2, C6H5NHCH3