KVS KOLKATA REGION
3rd
Time : 3 Hrs.
General instructions:
PRE-BOARD EXAMINATION- 2016
Class – XII
Sub.: Chemistry
F.M. : 70
i)
All questions are compulsory.
ii)
Marks for each question are indicated against it.
iii)
Questions number 1 to 5 are very short-questions, carrying 1 mark each.
iv)
Questions number 6 to 10 are short-answer questions, carrying 2 marks each.
v)
Questions number 11 to 22 are short-answer questions, carrying 3 marks each.
vi)
Questions number 23 is a value based question carrying 4 marks.
vii)
Questions number 24 to 26 are long-answer questions, carrying 5marks each.
viii)
Use log tables if necessary. Use of calculators is not permitted.
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1. Why is osmotic pressure of 1 M KCl higher than 1 M Urea Solution?
1
2. Draw the structure of 4-methyl pent-3-en-2-one?
1
3 Name one hexadentate ligand ?
1.
4 . Of physisorption or chemisorption, which has a higher enthalpy of adsorption? 1
5 .Name two poisonous gases which can be prepared from chlorine gas.
1
6. The chemistry of corrosion of iron is essentially an electrochemical phenomenon. Explain
the reactions occurring during the corrosion of iron in the atmosphere.
2
7. Silver crystallizes in face-centered cubic unit cell. Each side of this unit cell has a length of
400 pm. Calculate the radius of the silver atom. (Assume the atoms just touch each other on
the diagonal across the face of the unit cell. That is, each face atom is touching the four corner
atoms)
2
8. Explain what is meant by the following:
(i) peptide linkage
(ii) pyranose structure of glucose( either alpha or beta form).
2
9.. Write two structural differences between DNA and RNA.
2
10. How would you account for the following?
(i) Frenkel defects are not found in alkali metal halides.
. (ii) Impurity doped silicon is a semiconductor.
OR
Explain the following properties giving suitable examples:
(i) Ferromagnetism (ii)) Ferrimagnetism
11 Define the following terms giving one suitable example for each:
(i) Electrophoresis
(ii) Micelles
(iii) Peptization
2
3
12 Compare actinoids and lanthanoids with reference to their :
(i) electronic configurations of atoms
(ii) oxidation states of elements
(iii) general chemical reactivity of elements.
3
13. Write the name and structure of the monomer of each of the following polymer
(i) Nylon-6 (ii) Teflon
(iii) Neoprene
3
14. What type of a battery is the lead storage battery? Write the anode and the cathode
reaction and the overall reaction occurring in a lead storage battery sending out an electric
current.
3
OR
A voltaic cell is set up at 25°C with the half-cells
Ag+ (0.001 M) | Ag
and
Cu2+ (0.10M) | Cu
What should be its cell potential? (Ecello = 0.46 V, log 105 = 5)
15.Account for the following observations:
3
(i) pKb for aniline is more than that for methylamine.
(ii) Methylamine solution in water reacts with ferric chloride solution to give a precipitate of
ferric hydroxide.
(iii) Aniline does not undergo Friedel-Crafts reaction.
16 .Explain the basic principles of following metallurgical operations:
(i) Zone refining
(ii) Vapour phase refining
(iii) Electrolytic refining
3
17. Explain the following types of substance with one suitable example, for each case:
(i) Cationic detergents.
(ii) Food preservatives.
(iii) Analgesics.
3
18. (i) State one use each of DDT and iodoform.
3
(ii) Which compound in the following couples will react faster in SN2 displacement and why?
(a) 1-Bromopentane or 2-bromopentane
(b)1-Bromo-2-methylbutane or 2-bromo-2-methylbutane.
19. A mixed oxide of iron and chromium FeOCr2O3 is fused with sodium carbonate in the
presence of air to form a yellow colored compound (A). On acidification the compound (A)
forms an orange colored compound (B) which is a strong oxidizing agent. Identify the
compounds (A) and (B). Write balance chemical equation for each step.
3
20.(a) Write one use each of co-ordination compounds in the field of medicine and salt
analysis.
(b) Explain how the two complexes of nickel, [Ni (CN) 4 ]2- and [Ni (CO) 4] have different
structures but do not differ in their magnetic behaviour. (Ni = 28).
3
21.a) Give a chemical equation for each of the following reactions:
(i) Williamson’s synthesis
(ii) Reimer-Tiemann reaction
b)How will you convert Propene to Propan-1-ol
3
22.i) Explain the mechanism of Acid catalysed dehydration of an alcohol with the help of steps.
ii) Give equation of the reaction between Bromine(in CS2) with phenol
3
23) On a weekend Subham went on a picnic with his parents near a thermal power plant..
There was a beautiful view of lake but suddenly Subham saw some fish floating on the
surface of water of the lake as they had died. Subham asked his parents why these fish
had died. They told him that fish also need oxygen for their survival as we do.
4
After reading the above paragraph answer the following questions:
a) What values are posessed by Shubham?
b) Why does dissolved oxygen get depleted due to increase in temperature?
c) State Henry law.Write its mathematical expression and Draw graph.
24 (a) How will you prepare the following compounds starting with benzene?
i) Benzaldehyde
(ii) Acetophenone.
(b) Give chemical tests to distinguish between the following pairs of compounds:
(i) Ethanal and Propanal
(ii) Benzaldehyde and Acetophenone
(iii) Phenol and Benzoic acid.
OR
(a) Give chemical tests to distinguish between the following pairs of compounds:
i)Acetaldehyde and acetone
ii)Pentan-2-one and pentan-3-one
(b) How would you bring about the following conversions?
(i) Propanone to Propene
(ii) Ethanol to 3-hydroxybutanal
(iii) Benzaldehyde to Benzophenone.
25 a) Draw the structure of the following:
(i) H3PO2
(ii) BrF3
(b) How would you account for the following observations:
(i) Phosphorus has a greater tendency for catenation than nitrogen.
(ii) Bond dissociation energy of fluorine is less than that of chlorine.
(iii) No chemical compound of helium is known.
OR
5
5
(a) Draw the structures of the following:
(i) N2O5
(ii) XeOF4
(b) Explain the following observations:
(i) The electron gain enthalpy of sulphur atom has a greater negative value than that of
oxygen atom.
(ii) Nitrogen does not form pentahalides.
(iii) In aqueous solutions HI is a stronger acid than HCl
26 (a) Explain the following terms:
5
(i) Rate of a reaction
(ii) Activation energy of a reaction
(b) The decomposition of phosphine, PH3, proceeds according to the following equation:
4PH3(g)  P4(g) + 6H2(g)
It is found that the reaction follows the following rate equation:
Rate = k[PH3]
The half-life of PH3 is 37.9 s at 120°C.
How much time is required for 3/4th of PH3 to decompose?
OR
(a) Explain the following terms:
(i) Order of a reaction
(ii) Molecularity of a reaction
(b) The rate of a reaction increases four times when the temperature changes from 300 K to
320 K.Calculate the energy of activation of reaction, assuming that it does not change
with temperature. (R = 8.314 J K–1 mol–1)