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PRE BOARD EXAMINATIONS 2015
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Subject : CHEMISTRY
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Class
: XII
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Time : 3:00 HRS
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Max
Marks: 70
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Instructions
1.
All
questions are compulsory
2.
Q.
No 1 to 5 carry marks 1 each
3.
Q.
No 6 to 10 carry marks 2 each
4.
Q.
No 11 to 22 carry marks 3 each
5.
Q.
No 23 is value based question & carries 4 marks.
6.
Q.
No. 24 to 26 carry 5 marks each.
7.
Use
log tables, if necessary. Use of calculators is not allowed.
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01
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A compound
contains two types of atoms X & Y. It crystallises in a cubic lattice
with
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01
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simplest possible formula of this
compound?
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02
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Which compound in the following pair
undergoes SN1 reaction &
why?
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01
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and
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03
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Draw the structure of Hex 2 en- 4-yn-l-oic acid.
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01
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04
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Write down the IUPAC name of C6H5NHCH3
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05
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Why vitamin C cannot be stored in
the body?
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01
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06
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A solution of
Ni(NO3)2
is electrolysed between Pt-electrodes using a current of 5.0
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02
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ampere for 20
mints. What mass of Ni will be deposited at the cathode? (At. mass of
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Ni=58.7g)
OR
Write down the electrode reactions of
a Pb Storage battery during discharging.
7
The decomposition of NH3 on
Pt surface is zero order. What are the rates of 02 production of N2
& H2 if K=2.5X10-4 mol
L-1S-1?
a)
What
is the length of the side of the unit cell.
b)
What type of semiconductor is produced when
Si is doped with boron.
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12
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ofor the following
cell at 298 K
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03
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Mg(S)|Mg2+(10-3M)||Cu2+(10-4M)|Cu(s)
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Given, EoMg2+/Mg= -2.36V, EoCu2+/Cu =+0.34V
(1F=96500CMol-1)
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13
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nd
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03
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a) Write differential rate
equation b) 
c)
How is the rate affected when conc. of 
OR
a)
Derive
the integrated rate equation for 1st order reactions
b)
Give an example of a pseudo first order
reaction
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14
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Write the
principle involved in the refining of metals by the following methods
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03
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a)
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Zone refining
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b)
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Vapour phase refining
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c)
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Electrolytic refining
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15
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Account for the following :
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03
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a)
NH3 is a
stronger base than PH3
b)
Bi(v) is a strong oxidizing agent
c)
Bond dissociation energy of F2 is
less than that of Cl2
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16
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Write the
reactions involved in the manufacture of Sulphuric acid by contact process
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03
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17
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Draw the diagram
for crystal field splitting of d-orbital is octahedral field. On the
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basis
of crystal field theory., write the electronic configuration of d4
in terms of t2g &
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eg in octahedral
field when
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a)
o>P
o>P
b)
o<P
o<P |
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Page 3 of 4
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18 Account for the following
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a)
Haloarenes are less reactive towards
nucleophilic substitution reactions
b)
Grignard
reagents should be prepared under anhydrous conditions
c)
Melting point of p- dichlorobenzene is more
than O & m isomers
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19 i.
Chemically distinguish between
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a)
Aniline
& Ethylamine
b)
Methyl amine & dimethylamine
ii.
Complete
the reaction:
C6H5N2Cl +
H3PO2 + H2O
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20
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What do you understand about the
following, supply suitable examples (if any)
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03
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a)
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Denaturation of
proteins
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b)
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Inversion of sugar
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c)
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Peptide linkage
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21
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a)
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What are
thermosetting and thermoplastic polymers. Give one examples of each.
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03
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b)
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Arrange the following in increasing
order of their intermolecular forces
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Nylon 6,6 , Buna-S, Polythene
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22
a) How do antiseptics differ from
disinfectant? Name a substance which can act 03 both as an antiseptic and a
disinfectant at different concentration.
b)
Why
is the use of aspartame limited to cold food & drinks?
23 In thermal power stations, coal is
burnt to produce steam for generation of electricity. 04
The smoke produced is
passed through electrostatic precipitators Answer the following:
a)
Why
is the smoke passed through electrostatic precipitators?
b)
Which
property of colloidal solution is used in an electrostatic precipitator?
c)
How does coal ash effect environment?
d)
Which
value is promoted through the use of this precipitators?
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24 i.
What do you mean by the following:
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a)
Ideal solution
b)
Azeotrope
c)
Vapour pressure
ii. A
solution of glucose (C6H12O6) in
water is labeled as 10% by weight. What would be the molality of the solution?
(molar mass of glucose = 180 gmol-1)
OR
i. Define
osmotic pressure. Mathematically, show that how osmotic pressure of a solution
is used to calculate molar mass of a solute.
ii. 1.00g
of a non-electrolyte solute dissolved in 500g of benzene lowered the freezing
point of benzene by 0.40k. The Kf for
benzene is 5.12KKgmol-1. Find the molar mass
of the solute.
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Page 4 of 4
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25 i.
Complete the following chemical equations
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05
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a)
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Cr2O72- + H+ + I-
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b)
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MnO4
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- + Fe2+ + H+
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ii.
What is Lanthanoid Contaction? What is its cause? Write its two
consequences?
OR
i.
Give
reasons :
a) Although
F is more electronegative than O, the highest Mn fluoride is MnF4
whereas the highest oxide is Mn2O7
b)
The transition metals & their compounds
are generally colored.
c)
Transition metals act as good catalyst.
ii. Write
the reactions involved in the preparation of KMnO4 from
pyrolusite (MnO2) ore.
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26 i.
Write the steps involved in the conversion of
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a)
Aceto phenone to ethyl benzene
b)
Benzoic
acid to benzaldehyde
ii.
Give
reasons
a)
Carboxylic acids are stronger acid then
phenol
b)
Acetaldehyde
gives aldol condensation while formaldehyde does not.
c)
Cyclohexanone
forms cyanohydrins in good yields but 2,2,6- trimethyl cyclohexanone does not.
OR
i.
Complete
the following reactions
a)
CH3CHO dil
NaOH
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b)
C6H5COOH
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Conc HNO
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+ Conc H SO
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3
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2 4
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- An
organic compound (A) with molecular formula C8H16O2
was hydrolysed with dil H2SO4
to give a carboxylic acid (B) and alcohol (C). Oxidization of C with
chromic acid gives B,. C on dehydration gives but-1-ene. Identity A, B,
& C & also write the equations for the reactions involved.
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