Saturday, May 25, 2019

NEB-Grade- XII Chemistry Question-2076 (2019)

NEB-Grade- XII Chemistry Question-2076 (2019)
Sub. Code: 212 ‘B’
Time: 3hrs                                                                               Full Marks:75
                                     Pass Marks: 27 (only for partial students)
Candidates are required to give their answers in their own words as far as practicable. The figure in the margin indicates full marks.
Group ‘A’
Attempt any fifteen questions.                                                          15x2=30
1.    How would you confirm that B in BF3 gets SP2 hybridization?
2.    Distinguish between decinormal and decimolar solution.
3.    Find the PH of 1x10-5 N H2So4.
4.    How many coulombs are required to produce?
                     i.        27gm of silver from AgNO3?
                    ii.        50gm of Aluminum from Al2O3?
[At. Wt. of Ag= 108, At. wt. of Al=27]
5.    Define state function. Write any two examples of it.
6.    Calculate entropy change (ΔS) and free energy change (ΔG) for the conversion of ice into water at equilibrium condition when enthalpy change (ΔH) is 9KJ/ mol.
7.    You are given a rate law equation, Rat= K [A]2 [B]. By how many times will the rate increase or decrease for the reaction if
8.    Write down correct reactions for the conversion of ethyne into BHC.
9.    Why is haloarene less reactive than benzene in electrophilic substitution reaction?
10.  Starting from phenol how would you obtain
i.             phenolphthalein
ii.            p-hydroxy azobenzene.
12.  An organic compound C3 H6 O gives orange precipitate with 2-4 dinitrophenyl hydrazine but does not produce silver mirror with tollen’s reagent. Identify the compound and write the reaction involved.
13.  Why is nitro group called an ambident group?
14.  Write an example of each of the following reactions:
i.             Decarboxylation
ii.            Coupling reaction
15.  Write down the functional isomer of methyl methanoate. What product would you expect when the isomer is heated with P2 O5?
16.  How does DNA differ from RNA in respect of sugar and base units present in it?
17.  Define sugar and non-sugar giving an example of each.
18.  Mention an important function of each of the following:
i.             DDT
ii.            Nitrogen fertilizer
iii.           Broad spectrum antibiotics
iv.           Tranquilizers
19.  What is meant by homo-polymerization? Write an example of such polymer.
20.  How is lithophone prepared? Write its one important application.
21.  Why is silver nitrate solution used for staining fingers of voters during election?
22.  What is meant by
i.             quenching of steel
ii.            annealing of steel
Group ‘B’
Attempt any five questions.                                                     5x5=25
23.  Are all standard solutions, primary standard solutions or not? Give reason.
I am of a divalent metal was dissolved in 25ml of 2NH2SO4 (f= 1.01). The excess acid required 15.1ml of 1N-NaOH (f=0.8) for complete neutralization. Find the atomic weight of the metal. 
24.  Mention the important application of standard hydrogen electrode. 
i.             Draw the standard cell notation.
ii.            Identify the anode and cathode as the current drawn from it.
iii.           Write the cell reaction taking place at the electrodes.
iv.           Calculate standard cell potential.
25.  Define bond dissociation energy. The bond dissociation energy of H2(g) and Cl2 (g) are 435 KJ/ mol and 243 KJ / mol respectively. The enthalpy of formation of HCl(g) = - 92 KJ/mol. Calculate the bond dissociation energy of HCl(g).
26.  How is blister copper extracted from copper pyrites?
27.  Starting form CH2 Mgl how would you prepare
i.             Propan-2-ol
ii.            2- methyl propan-2-ol.
28.  How is trichloromethane prepared in the laboratory? Why is chloroform stored in a dark room air tied bottle containing a little ethyl alcohol?
Group ‘C’
Attempt any two questions.                                                    2x10=20

 The compound  can be obtained by heating toluene in presence of  CeO2 / H+.
   31.  a. How is ethanal prepared from
i.             ethyne
ii.            But-2-ene
iii.           1, 1-dichloroethane?
Write down suitable method for the conversation of ethanal into 2-hydroxy propanoic acid.
b.          Write down a structural formula of primary, secondary and tertiary amine of each from C3 H9 N. How is Hoffmann’s method applied to separate them from their mixture?
         32.  Define the terms
i.           activation energy
ii.          order of reaction
iii.         molecularity of reaction
iv.         effective collision
v.          rate law equation. 
Why does powder sugar dissolve faster than grain sugar?
The following data were obtained for a hypothetical reaction
[x] mol L-1
[y] mol L-1
Formation of z mol L-1 S-1
1.     1
2.     2
1.2 x10-2
3.     3
4.     4
  Calculate the rate constant and find out rate of disappearance of y when [x]=0.2 mol L-1.
33.   Write short notes on any two.                                                 2x5=10
i.             Chemistry of rusting theory of iron
ii.            Extraction of mercury from cinnabar
iii.           Laboratory preparation of anhydrous formic acid
iv.           Lewis concept of acid and base.

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