KENDRIYA VIDYALAYA BASTI
PRE-BOARD I 2015-16
CLASS: XII
SUBJECT:
CHEMISTRY (Theory)
MAX.MARKS: 70TIME-ALLOWED: 3 HRS
General Instructions:
a) All the questions are compulsory.
b) There are 26 questions in total.
c) Questions 1 to 5 are very short answer type questions and carry one mark each.
d) Questions 6 to 10 carry two marks each.
e) Questions 11 to 22 carry three marks each.
f) Questions 23 is value based question carrying four marks.
g) Questions 24 to 26 carry five marks each.
h) There is no overall choice. However, an internal choice has been provided in one question of twomarks,
one question of three marks and all three questions in five marks each. You have to attempt only one of
the choices in such questions.
i) Use of calculators is not permitted. However, you may use log tables if necessary.
1.
2.
3.
4.
5.
What is peptide bond?
Which will be absorbed more readily on the surface of charcoal and why- NH3 or CO2?
A compound having formula C3H5O2Br is optically active. What is its structure?
Ethanoic acid is highly soluble in water but hexanoic acid is only slightly soluble in water. Why?
Write the IUPAC name of following compound:
CH3 –CH2-CO-NH-CH3
6. An element exist in FCC structure with cell edge of 288 pm. If density of the element is 7.2 gcm,-3 what is
atomic mass of that element?
7. Write the balanced chemical equation for the following reaction:
(a) PCl3 + H2O 
(b) XeF6 +H2O
8. The chemistry of corrosion of iron is essentially an electrochemical phenomenon. Write the reactions
occurring during corrosion of iron in the atmosphere.
9. a. What type of stoichiometric defect is shown by a– ZnS & b-AgBr
.
b. What is the effect on density of a crystal due to schottky defect?
10. A reaction is second order with respect to a reactant. How is the rate of reaction affected if the concentration
of reaction is:
(a) Doubled
(b) Reduced to half
OR
Define pseudo unimolecular reaction. Write one example.
11. a. Amino acids may be acidic, alkaline or neutral. How does this happen?
b. What are reducing sugars ? Give one example.
12. Arrange the compounds of each set in order of reactivity towards S N 2 displacement.
a)2-Bromo-2-methylbutane, 1-Bromopentane, 2-Bromo pentane.
b)What happens when
Bromobenzene is treated with Mg in the presence of dry ether
c)Haloarenes are chemically less reactive than haloalkanes, explain why?
13. Complete the following reactions:
a)
CH 3CH 2 Br  NH 3 
dryether
b) C6 H 5  Cl  Na 
b) n-butyl chloride is treated with alcoholic KOH
14. (a) Give difference between antiseptic and disinfectants with example.
(b )What is the use of bithional in soaps?
OR
Define the following substances. Give one example each:
(a) Antacid
(b) Antifertility drug.
(c) Antioxidants
15. Which of the following solution has larger molar conductance:
(a) 0.20 M solution which has resistivity equal to 58 Ωcm
(b) 0.20 M solution having conductivity equal to 2.5 X 10-2 Ω-1cm-1.
16. Sucrose decomposes in acid solution into glucose and fructose according to first order rate law with t1/2= 4
hours. What fraction of sample of sucrose remain after 7 min?
17. Account for the following observation:
a) N2 is less reactive at room temperature.
b)H2Te is more acidic than H2s.
c)Flourine is stronger oxidising agent than chlorine.
18. (a) Write the two main differences between the properties of white phosphorous and red phosphorous.
(c) Why does chlorine water loses its yellow colour on standing?
19. What happens whena) a beam of light is passed through a colloidal solution.
b) an electrolyte NaCl is added to hydrated ferric-oxide sol.
c) electric current is passed through a colloidal solution.
20. Describe the role of:
(a) NaCN in the extraction of gold from gold ore.
(b) SiO2 in the extraction of copper from copper matter.
(c) Iodine in the refining of zirconium.
(Write the chemical equations for the involved reactions)
21. For the complex K3[Fe(CN)6], identify:
(a) The oxidation number of iron.
(b) The hybrid orbital.
(c) Shape of complex.
(d) The magnetic behaviour of complex.
(e) Name of the complex.
(f) Coordination - entity
22. (a) out of the two bases named below which one is present in RNA and which one is present in
DNA?
(i)
Thymine
(ii)
Uracil
(b) Name the vitamin responsible for the coagulation of blood.
(c) Name the expected products on hydrolysis of lactose.
23. After watching a programme on TV about the adverse effects of junk food and soft drinks on the health of
school children, Sonali, a student of Class XII discussed the issue with the school Principal. Principal
immediately instructed the canteen contractor to replace the fast food with the fibre and vitamin rich food
like sprouts, salad, fruits etc. This decision was welcomed by the parents and the students.
After reading the above passage, answer the following questions:
a) What values are expressed by Sonali and the principal of the school?
b) Give two examples of water –soluble vitamins.
c) Name the disease caused by deficiency of these vitamins.
24. (a) Will the depression in freezing point be same or different if 0.1 mole of sucrose or 0.1 mole of glucose is
dissolved in 1Litre of water. Also explain the reason.
24.
(b) calculate the amount of KCl which must be added to 1Kg of water so that freezing point is depressed by
1.8 K. (Kf for water =1.86 K Kg/mol, molecular weight of KCl = 74.5)
OR
(a) What is reverse osmosis. Pressure applied on the solution should be larger than osmotic pressure.
(b) What will be the value of Vonthoff’s factor for a dilute solution of K2SO4 in water?
(c) A 2% aqueous solution of a non-volatile solute exerts a vapour pressure of 1.004 bar at 100oC. what is
the molar mass of solute?(given: vapour pressure of pure water at 100oC is 1.013 bar and molar mass of
water is 18 g/mol)
25. (a) Account for the following:
i) Transition metal show highest oxidation state in their oxides than flourides
ii) Why are Mn2+ compounds are more stable than Fe2+ compounds towards oxidation to their +3
Oxidation state.
iii) Ionisation enthalpies of lanthanides is lower than actinides.
b) Complete the following chemical reactions:
(i)
(ii)
Cr2O72- + H+ + I-
MnO4- + H+ + Fe2+
OR
(a) What is the effect of pH on the solution of K2Cr2O7 solution?
(b) Explain giving reasons:
(i)
Transition metal and many of their compounds show paramagnetic behaviour.
(ii)
Transition metal and their many compound act as good catalyst.
(iii)
Europium (II) is more stable than cerium(II).
26. (a) Give chemical test to distinguish between following pairs of compounds:
(i) Ethanol and propanol
(ii) Phenol and benzoicacid
(b)Complete the following chemical reactions:
(i) 2HCHO + NaOH
(ii) CH3COCH3 + CH3MgBr --------H2O
CO, HCl
(iii) C6H6
-------
Anhyd. AlCl3
OR
(a) llustrate the following name reactions giving example:
(i) Clemmensen reduction
(ii) Hell volhard-Zelinsky reaction
(b)Give reasons:
(i) Carboxylic acids have higher boiling points than alcohols of comparable molecular mass.
(ii) Chloroacetic acid has lower pKa than acetic acid.
(iii) Arrange the following in increasing order of their reactivity towards nucleophillic addition reactions:
Ethanol, butanone, propanone, propanal.
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