Chemistry NEB 2081 question paper

Group A

Very short answer questions(11 × 1 = 11)

Group B

Short answer questions(8 × 5 = 40)

1. 12.

   An electrochemical cell (galvanic cell) is designed by coupling Zn-electrode with standard hydrogen electrode (SHE). Given, $E_{Z{n}^{++}/Zn}=-0.76V$.

   • i) Draw the galvanic cell. [2]
   • ii) Write down complete cell reaction. [2]
   • iii) Calculate the emf of the cell. [1] OR What is Hess's law of constant heat summation ? Calculate the heat of formation of ethanol from the following data : [1+4]
   • $\mathrm{H}{}_2(\mathrm{g})+\frac{1}{2}\mathrm{O}{}_2(\mathrm{g})\to \mathrm{H}{}_2\mathrm{O}(\mathrm{l})$, $\Delta H=-286.2KJ/mol$
   • $\mathrm{C}(\mathrm{s})+\mathrm{O}{}_2(\mathrm{g})\to \mathrm{CO}{}_2(\mathrm{g})$, $\Delta H=-393.2KJ/mol$
   • $\mathrm{C}{}_2\mathrm{H}{}_5\mathrm{OH}(\mathrm{l})+3\mathrm{O}{}_2(\mathrm{g})\to 2\mathrm{CO}{}_2(\mathrm{g})+3\mathrm{H}{}_2\mathrm{O}(\mathrm{l})$, $\Delta H=-1368KJ/mol$

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2. 13.

   Define the following terms.

   • i) Lewis base
   • ii) Basic buffer [2]
   • Calculate the pH of solution obtained by mixing equal volumes of two solutions having $pH=3$ and $pH=5$. [

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3. 14.

   A heavy metal is extracted from its oxide ore. During extraction, smelting of the calcined ore is done in a blast furnace.

   • a) Name the metal and the ore.
   • b) Draw the clean and labelled diagram of the blast furnace showing different zones.
   • c) Write down the balanced chemical equations of slag formation reactions. [5]

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4. 15.

   Write two methods of preparation of corrosive sublimate. [2] Give its action with

   • a) excess of KI [2]
   • b) $\mathrm{NH}{}_3$ [1]

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5. 16.
   • i) Starting from nitrobenzene, how would you prepare aniline ? Convert aniline into : [1]
     • a) phenyl isocyanide [1]
     • b) azo-dye [1]
   • ii) Nitrobenzene prefers electrophilic substitution reaction at meta-position. Explain. [2]

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6. 17.

   A sequence of chemical reactions is represented as: $A\underset{\text{Ice cold}}{\overset{\mathrm{NaNO}{}_2+\mathrm{dil}\cdot \mathrm{HCl}}{\to }}B\underset{[\mathrm{O}]}{\overset{\mathrm{KMnO}{}_4/\mathrm{H}{}^{+}}{\to }}\mathrm{CH}{}_3\mathrm{CHO}$

   • a) Identify the compounds (A) and (B). [1]
   • b) Write the laboratory test of compound (B). [1]
   • c) Starting from compound (B), how would you obtain nitrolic acid ? [2]
   • d) Predict the product when compound (A) is heated with chloroform in alcoholic medium. [1] OR Make a correct sequence of reactions using suitable conditions and reagents of the following compounds. Benzene, Benzaldehyde, Toluene, Cinnamic acid, Sodium benzoate, Benzoic acid.

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7. 18.

   Write a chemical equation for each of the following.

   • a) 2, 4- DNP test [1]
   • b) Oxo-process [1]
   • c) Claisen condensation reaction [1]
   • d) Wurtz-Fittig reaction [1]
   • e) Carboxylation reaction [1]

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