Chemistry - Kendriya Vidyalaya No. 2 Kalaikunda

KENDRIYA VIDYALAYA SANGATHAN, KOLKATA REGION
2 Pre Board Examination – 2014-15
nd
Class XII
Subject: Chemistry
Time allowed : 3 hours
Maximum marks: 70
General instructions:
(i) All questions are compulsory.
(ii) Question numbers 1 to 5 are very short answer questions & carry 1 mark each.
(iii) Question numbers 6 to 10 are short answer questions & carry 2 marks each.
(iv) Question numbers 11 to 22 are also short answer questions & carry 3 marks each.
(v) Question number 23 is a value based question & carry 4 marks.
(vi) Question numbers 24 to 26 are long answer questions & carry 5 marks each.
(vii) Use log tables, f necessary. Use of calculators is not allowed.
----------------------------------------------------------------------------------------------------------------------------------------------.1) Write an example of an anti ferro magnetic substance.
[1]
. 2) What is a colloidion?
[1]
3) Write the IUPAC name of ionization isomer of [Co(H2O)5Cl ]SO4. H2O.
[1]
4) Which isomer of C4H9Br undergoes SN1 reaction easily & why?
[1]
.5) Explain: Aniline does not undergo Friedel-Crafts reaction.
[1]
6) The vapour pressure of pure benzene at a certain temperature in 0.85 bar. A non volatile,
non electrolyte solid weighing 0.5 g when added to 39.0 g of benzene (molar mass 78 g/mol).
the Vapour pressure of the solution is then 0.845 bar. What is the molar mass of the solid
substance?
[2]
.7) (a) What is the order & molecularity of the following elementary reaction:
2A + B → D; the rate law expression is r=k [A] ½ [B] ?
(b) How does a catalyst affect the rate of a chemical reaction ?
[2]
8) (a) Which is more stable & why- white phosphorus or red phosphorus?
(b) Write the reaction of thermal decomposition of sodium azide.
[2]
Or
(a) Although electron gain enthalpy of fluorine is less negative than that of chlorine, fluorine
is a stronger oxidizing agent than chlorine. Why?
(b) Complete the equation: Cl2 + NaOH (hot & conc.) → ?
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KVS RO, Kolkata 2 Pre Board examination 2014-15 Class XII (Chemistry Question paper)
[2]
.9) (a) What is misch metal & write one of its uses?
(b) A black ore of manganese on fusion with an alkali (KOH) and oxidizing agent (O2)
forms a dark green mass. Write the chemical equation involved.
[2]
.10) (a) Write the IUPAC name of CH3COCH=C(OH)CHO.
(b) Convert: acetaldehyde into propan-2-ol.
[2]
11) (a) Find the value of ‘i’ for K4[Fe(CN)6] solution with 100% dissociation.
(b) What type of a binary solution is formed when two miscible liquids A & B forms a
solution & the solution turns hot? What type of azeotrope does it form?
(c) Under what condition reverse osmosis takes place?
[3]
12) (a) Give an example of a reaction whose unit of rate of reaction & specific rate constant
is same.
(b)The rate constant for the first order decomposition of H2O2 is given by the following
reaction: log k = 14.34 – 1.25 x 104 K/T. Calculate Ea for this reaction at 298 K
[1+2]
13) (a) What happens when a few drops of AgNO3 solution is added to a test tube
containing KI solution & shaken?
(b) Why is a delta formed at the meeting point of sea & river?
(c) Give an example of a colloidal sol used as (i) an eye lotion & (ii) to cure kalaazar?
[3]
.14) (a) What is the role of silica in the metallurgy of copper?
(b) Is it true that under certain conditions, Mg can reduce Al2O3 and Al can reduce
MgO? What are those conditions?
(c) Write the principle of zone refining in an element purification process.
[3]
.15) Explain
(a) Cr2+ is a stronger reducing agent than Fe2+.
(b) Many copper (I) compounds are unstable in aqueous solution.
(c) Lanthanoid elements occur together in nature & difficult to separate.
16) (a) Write the electronic configuration of central metal ion, Fe2+ in an octahedral complex
for a strong ligand field according to crystal field theory.
(b) Why is geometrical isomerism not possible in tetrahedral complexes having two
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KVS RO, Kolkata 2 Pre Board examination 2014-15 Class XII (Chemistry Question paper)
[3]
different types of unidentate ligands coordinated with the central metal ion?
(c) Explain: [Ni(CN)4]2- is a tetrahedral diamagnetic complex ion.
[3]
Or
(a) Draw the stereoisomers of [Co(NH3)3(NO3)3]
(b) Draw figure to show the splitting of d orbitals in an octahedral crystal field.
(c) Explain: [Cu(en)2]2+ is more stable than [Cu(H2O)4]2+.
[3]
17) (a) Write the structure of the major products formed when C2H5ONa reacts with (CH3)3CCl.
(b) Explain why
(i) Grignard reagents should be prepared under anhydrous condition?
(ii) CH2=CHCH2-Cl undergoes SN1 reaction & not SN2 reaction as expected.
[3]
18) (a) Illustrate Cannizzaro reaction
(b) Give a chemical test to distinguih between :
(i) HCOOH & CH3COOH
(ii) Acetophenone & benzophenone.
[3]
19) (a) Account for the following:(i) pKb of aniline is more than that of methylamine.
(ii) Methylamine in water reacts with ferric chloride to precipitate hydrated ferric oxide.
(b) Convert: aniline into 4-nitroaniline as major product.
[3]
20) (a) If the radius of the octahedral void is r & radius of the atoms in closed packing is R ,
derive relation between r & R.
(b) Solid A is a very hard electrical insulator in solid as well as in molten state & melts at
very high temperature. What type of solid is it?
[3]
.21) (a) Identify the monomers in the following polymer:-[CO-(CH2)8-CO-NH-(CH2)6-NH]n(b) Write the full form of PHVB.
(c) Write the monomers of Bakelite.
22) (a) Give an example of (i) a cationic detergent (ii) an antioxidant.
(b) What is the advantage of using sucrolose over aspartame?
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KVS RO, Kolkata 2 Pre Board examination 2014-15 Class XII (Chemistry Question paper)
[3]
(c) Why are cimetidine or ranitidine better antacids than NaHCO3 or Mg(OH)2 or Al(OH)3?
[3]
23)* Neeta observed that her mother got tired after doing every little work. She took her mother
to a doctor. The doctor immediately put her mother on dextrose solution, diagnosed
pernicious anemia & gave instructions & medicines. Neeta helped her in household work till
she recovered & took her care.
(a) Name the vitamin whose deficiency causes pernicious anemia.
(b) What is the common name of ‘dextrose’? Draw its open structure.
(c) Write one important difference between starch & cellulose.
(d) Mention the values shown by Neeta.
24) (a) Complete the equation: (i) FeS2 + O2
[4]
?
(ii) P4 + NaOH + H2O
(iii) H3PO3
?
?
(c) Write the reactions involved in the brown ring test.
[5]
Or
(a) Give reason:
(i) PCl5 exists as an ionic crystalline solid.
(ii) Chlorine gas is a powerful bleaching agent.
(iii) Fluorine exhibits only -1 oxidation state whereas chlorine exhibits +1, +3, +5 and +7
oxidation states also.
(b) A colourless gas, ’A’ which is an oxide of nitrogen, turns into a reddish brown gas ‘ B’
when brought in contact with air. Gas ‘B’ again becomes colourless on cooling,forming gas
‘C’. Write the reactions involved in the observations.
25) (a) Explain: Rusting is prevented in alkaline medium.
(b) Suggest a way to determine the Λ°m value of water.
(c) Write the cathode reaction of H2-O2 fuel cell.
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KVS RO, Kolkata 2 Pre Board examination 2014-15 Class XII (Chemistry Question paper)
[5]
(d) Write the Nernst equation for Al(s)/Al3+(xM)//Zn2+(yM)/Zn(s) at 298K
[5]
Or
(a) Write the SI unit of molar conductivity.
(b) Calculate the potential of hydrogen electrode in contact with a solution whose pH is 10.
(c) Predict the products of electrolysis of aqueous solution of NaCl using Pt electrodes.
(d) A mercury cell has a constant cell potential throughout its life. Why?
[5]
26) (a) Write the mechanism of dehydration of ethanol by conc.H2SO4 at 443K.
(b) An organic compound ‘A’ having molecularformula C6H6Ogivec a characteristic colour
with aqueous FeCl3 solution. ‘A’ on treatment with CO2& NaOH at 400K under pressure
gives ’B’ which on acidification gives ’C’. The compound ‘C’ reacts with acetic anhydride to
give ’D’ which is a popular pain killer. Identify A, B, C & D.
(c) How can we separate the product formed by the reaction of phenol with dilute nitric
acid at low temperature(298K)?
[5]
or
(a) How is phenol manufactured from cumene?
(b) Explain:
(i) Denatured alcohol is unfit to drink.
(ii) Phenol undergoes electroplilic substitution at ortho and para positions.
(c) An organic compound ’A’ having molecular formula C8H16O2, was hydrolysed with
dilute H2SO4 to give a carboxylic acid’ B’, and an alcohol C.Oxidation of ‘C’ with chromic acid
produced ‘B’. ‘C’ on dehydration gives but-2-ene as the major product. Identify A, B and C and
write the reactions involved.
[1+2+2]
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KVS RO, Kolkata 2 Pre Board examination 2014-15 Class XII (Chemistry Question paper)