Q30 of 30 Page 1

(a) Although phenoxide ion has more number of [5] resonating structures than Carboxylate ion, Carboxylic acid is a stronger acid than phenol. Give two reasons.

(b) How will you bring about the following conversions?


(i) Propanone to propane


(ii) Benzoyl chloride to benzaldehyde


(iii) Ethanal to but-2-enal


OR


(a) Complete the following reactions:


(i)


(ii)


(iii)


(b) Give simple chemical tests to distinguish between the following pairs of compounds: ‘


(i)Ethanal and Propanal


(ii)Benzoic acid and Phenol



(a) Although phenoxide ion has more number of [5] resonating structures than Carboxylate ion, Carboxylic acid is a stronger acid than phenol. This is due to the formation of equivalent resonance structures for carboxylate ion and this lacks for phenoxide ion.


In carboxylate ion the negative charge is effectively delocalized over two oxygen atoms whereas it is less effectively delocalized over one oxygen atom and less electronegative carbon atom.



Resonance structures of phenoxide ion



Resonance structures of carboxylate ion


(b)


(i) If propanone is reduced Zinc amalgam in HCl, we get propane. This process is called Clemmensen Reduction.



(ii) When benzoyl chloride is treated with H2 and poisoned Pd in BaSO4, it is reduced to benzaldehyde.



(iii) Ethanal is converted to but-2-enal by a process called aldol condensation.


First aldol of ethanol is done by treating it with NaOH, that is we get 3-hydroxybutanal which on condensing gives but-2-enal.



OR


(a)


(i) Since formaldehyde has no α Hydrogen, Cannizaro reaction takes place thereby forming methanol and potassium formate.



(ii) CH3COOH under Br2 and red Phosphorus gives α-bromoacetic acid. This reaction is called HVZ (Hell-Volhard-Zelensky) reaction.



(b)


(i) Ethanal and Propanal


Aldehydes and ketones having at least one methyl group linked to the carbonyl carbon atom responds to the iodoform test. Ethanal having one methyl group linked to the carbonyl carbon atom responds to this test. But propanal does not have a methyl group linked to the carbonyl carbon atom and thus, it does not respond to this state.



(ii) Benzoic acid and Phenol


Phenol reacts with neutral FeCl3 to form an iron-phenol complex giving violet colouration.



But benzoic acid reacts with neutral FeCl3 to give a buff coloured ppt. of ferric benzoate.



More from this chapter

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26

After watching a programme on TV about the adverse effects of junk food and soft drinks on the health of school children, Sonali, a student of Class XII, discussed the issue with the school principal. Principal immediately instructed the canteen contractor to replace the fast food with the fibre and vitamins rich food like sprouts, salad, fruits etc. This decision was welcomed by the parents and the students.

After reading the above passage, answer the following questions:


(a) What values are expressed by Sonali and the Principal of the school?


(b) Give two examples of water-soluble vitamins.


 27

(a) Which one of the following is a food preservative?

Equanil, Morphine, Sodium benzoate


(b) Why is bithional added to soap?


(c) Which class of drugs is used in sleeping pills?


 28

(a) A reaction is second order in A and first order in B.

(i) Write the differential rate equation.


(ii) How is the rate affected on increasing the concentration of A three times?


(iii) How is the rate affected when the concentrations of both A and B are doubled?


(b) A first order reaction takes 40 minutes for 30% decomposition. Calculate t1,2 for this reaction.


(Given log 1.428 =0.1548)


OR


(a) For a first order reaction, show that time required for 99% completion is twice the time required for the completion of 90% of reaction.


(b) Rate constant 'k' of a reaction varies with temperature 'T' according to the equation:



Where, Ea is the activation energy. When a graph is plotted for log k Vs. a straight line with a slope of –4250 K is obtained. Calculate 'Ea' for the reaction.


(R = 8.314 JK–1 mol-1).


29

(a) Give reasons for the following:

(i) Bond enthalpy of F2 is lower than that of Cl2.


(ii)PH3 has lower boiling point than NH3.


(b)Draw the structures of the following molecules:


(i)BrF3


(ii)(HPO3)3


(iii)XeF4


OR


(a) Account for the following:


(i) Helium is used in diving apparatus.


(ii) Fluorine does not exhibit positive oxidation state.


(iii)Oxygen shows catenation behavior less than sulphur.


(b)Draw the structures of the following molecules:


(i)XeF2


(ii)H2S2O8