SET - III
KENDRIYA VIDYALAYA SANGATHAN, CHENNAI – 36
COMMON PRE-BOARD EXAMINATION 2011-12
SUBJECT : CHEMISTRY
CLASS – XII
MAX. MARKS : 70
TIME : 3 HRS.
Instructions

Answer all questions.

Questions 1 to 8 carry one mark each. Answer them in one word or sentence.

Questions 9 to 18 are short answer questions and carry two marks each.

Questions 19 to 27 are also short answer questions and carry three marks each.

Questions 28 to 30 are long answer questions and carry 5 marks each.
1. What are the physical state of dispersed phase and dispersion medium of emulsion?
2. The formula of a compound is A2B3 with a hcp lattice. What fraction of tetrahedral voids
are occupied?
3. What is the purpose of adding xanthates to sulphide ores?
4. What is the charge on the sol formed when KI is added to excess AgNO3?
5. Pentavalent Bismuth is a strong oxidizing agent.Why?
CH3
6. Write IUPAC name of
CHO
7. What is carbylamine reaction?
8. Both cellulose and starch are made up of glucose units. Starch can be digested by
humans but cellulose cannot be digested. Why?
9. (i) What is the reason for abnormal molecular mass of solute?
(ii) A person suffering from high blood pressure should take less common salt. Why?
10. Give reason
a) 1 gm. of pulverized wood burns faster than 1 gm. of a piece of wood.
b) Reactions of higher molecularity are rare.
11. How will you distinguish between o/w and w/o emulsions?
12. The free energies of formation of FeO(s) and CO(g)are given at 673K and 1073K.
 GFeO0= -375 kJ/mol ,  GCO= -325 kJ/mol at 673K
 G 0FeO= -275 kJ/mol ,  G 0CO = -450 kJ/mol at 1073K
On the basis of the above data, predict the temperature at which carbon can be used as
a reducing agent for FeO.
13. Give reasons(i)
SF 6 does not undergo hydrolysis
(ii)
NO becomes brown when released in air.
14. In the titration of Fe 2+ ions with KMnO4 in acidic medium why dilute H2SO4 is used and
not dil. HCl. Give necessary equations.
OR
An orange coloured solution A changes to an yellow coloured solution B on increasing
the pH and the reverse happens on decreasing the pH.Identify A and B and give
equations.
15. Which one undergoes SN1 reaction faster?
1)C6H5CH2Br or (C6H5 )2 CHBr
2) CH2 =CH-CH2Cl or CH2=CH-CH2I
16. (i)Why chloroform has to be stored in dark coloured bottles?
(ii) Why aryl halides do not undergo nucleophilic substitution reactions easily?
17.Complete and name the reactions
CHCl3/NaOH
1. C6H5OH
2. C6H5OCH3
?
CH3Cl / Anh. AlCl3
?
18. Carry out the conversions
(i)
Propene to propan-1-ol
(ii) Ethanol to but-1-yne
19. Copper crystallizes into a FCC lattice with edge length 3.61x10-8cm. Show that the
calculated density is in agreement with its measured value of 8.92gm/cm3. (Atomic mass
of Copper = 63.5).
20. When a solution is prepared , 100kJ of heat energy is released. What type of deviation
will the solution show from Raoult’s law? Explain with a graph and give an example of
such a solution.
21. The decomposition of PH 3 proceeds according to the reaction
4 PH3
P4
+ 6 H2
It is found that the rate of reaction follows the rate equation, rate=k[PH3]. The half life
of PH3 is 37.9 s at 120 0C.
(i)
How much time is required to decompose ¾ th of initial PH3?
22. (i) Co2+ is stable in aqueous solution but in the presence of complexing agents get
oxidized to Co3+.
(ii)
Cu(I) is highly unstable in solutions
(iii)
Zr and Hf have same properties.
23. Differentiate between antiseptics and disinfectants? Give one substance which acts
both as antiseptic and disinfectant.
24. A metal ion M n+ having d4 valence electronic configuration combines with three
didentate ligands to form a complex. Assume  0 >P
(i)
Draw diagram showing d orbital splitting during this complex formation
(ii)
Write the electronic configuration of the valence electron of the metal ion in
terms of t2g and eg.
(iii)
Name the type of isomerism exhibited by this complex.
25. Account for the following(i)
pKb of aniline is more than ethyl amine
(ii)
Tertiary amines do not give acylation reactions.
(iii)
Sulphanilic acid is insoluble in water but soluble in aqueous bases and aqueous
acid taken separately.
26. Explain free radical polymerization of ethylene.
OR
How is Nylon-6 is prepared? What is indicated by 6 in Nylon-6?
27. Identify and name the following
(i)
Building blocks of protein which must be supplied in the diet
(ii)
Storage form of carbohydrates in animals
(iii)
Water soluble vitamin that can be stored.
28. (i) State and explain Kohlrausch’s law.
(ii)For the cell reaction 2Fe3+ + 2I-
Fe2+ + I2 (E0 cell = 0.236 at 298K). Calculate
 G and K.
OR
(i)
What is a fuel cell? Write the reactions taking place at cathode and anode of
H2-O2 fuel cell.
(ii)
Write Nernst equation and calculate emf of the cell:
Fe(s)/ Fe2+ (0.001M) || H+(1M)/H2(g)(1 bar)/Pt(s) E0 Fe2+/Fe = -0.44V.
29. Identify A to E and write the reactions involved.
Mg
CH3Br
CO2
A
H2O
B
i.Cl2/P
C
NH3
D
E
ii. H2O
OR
A compound A with molecular formula C5H10O gave a positive 2,4-DNP test but negative
Tollen’s and iodoform test It was oxidized to carboxylic acid B with molecular formula
C3H6O2 when treated with alkaline KMnO4 under vigorous oxidation. Sodium salt of B
gave a hydrocarbon C on Kolbe’s electrolyte method. Identify A,B,C and write the
reactions involved.
30. An element ‘A’ exists as a yellow solid in standard state. It forms a volatile hydride ‘B’
which is a foul smelling gas and is extensively used in qualitative analysis of salts. When
treated with oxygen, ‘B’ forms an oxide ‘C’ which is a colourless, pungent smelling gas.
This gas when passed through acidified KMnO4 solution, decolourises it. ‘C’ gets oxidized
to another oxide ‘D’ in the presence of a heterogeneous catalyst. Identify A,B,C,D and
also give the chemical equation of reaction of ‘C’ with acidified KMnO4 solution and for
conversion of ‘C’ to ‘D’.
[5]
OR
(a) Complete the following reactions:
(i) XeF4 + PF5
(ii)U + 3ClF3
(iii) Ca3P2 + H2O
?
?
?
(b) Give the structures of pyrophosphoric acid and XeO3.