CBSE Sample Paper XII Chemistry




TIME: 3 HOURS                                                                                       MAX. MARKS: 70
General Instructions:
  1. i.                    All questions are compulsory.
  2. ii.                  Questions 1 to 5 are very short answer type carrying 1 mark each. Answer them in one sentence each.
  3. iii.                Questions 6 to 12 are short answer type carrying 2 marks each. Answer each of them in about 30 words.
  4. iv.                 Questions 13 to 24 are also short answer type carrying 3 marks each. Answer each of them in about 40 words.
  5. v.                    Questions 25,26&27 are long answer type carrying 5 marks each. Answer each of them in about 70 words.
  6. Calculators are not permitted. Use log tables if necessary.                                              
  1. Why is solubility of O2 in water decreases with increase of temperature?
  2. Rate constant of forward reaction measured at 298K is 2.3 X 10-4 S-1. Find the

rate constant for the reverse reaction                                   

  1. Write IUPAC name of the compound:

          CH3 –CH –CH2 –COO CH2-CH3


  1. How are amines purified from non-basic impurities?
  2. A 1 molal aqueous solution of glucose has lower boiling point than 1 molal aqueous

solution of common salt.

  1. How is hydrogen sulphide prepared in the laboratory? Write only equation. Also name the apparatus used. Arrange the hydrides of group 16 in the increasing order of acidity.
  2. (a) What is isoelectric point of an amino acid?

      (b) Write chemical equation to show the formation of peptide linkage-Gly-Ala.

  1. (a)  Write the electrode reactions of the H2—O2 fuel cell.

(b) How many Faradays of charge are needed to reduce one mole of Manganate ion

to Permanganate ion?

  1. Show the shape of bonding and antibonding molecular orbitals formed by combination of (a) two s orbitals

(b) two p orbitals (side to side)

  1. What are co-polymers and homo-polymers? Give one example for each kind.
  2. Consider the molecule: HOOCCHBrCH2CHBrCOOH

(a) Draw any enantiomer pairs (b) Any diastereomeric pairs (c) A meso form.

  1. How will you distinguish the following pairs of organic compounds?

1-propanol & 2-methyl 2-propanol

Acetonitrile and nitroethane

  1. Explain the following terms:

(a)    Reversible sols(b) Tyndall Effect (c) Electrodialysis

  1. (a) A sample of freshly cut wood from a tree contains 10mg of C-14. How much C-14 will remain in the wood sample after 5 x 104 years? t1/2 of C-14 = 5700 years.

      (b) Complete the following nuclear reaction:

9Be4(a, n) ——————                                                                                       

  1. How are lipids classified? Write their functions.
  2. (a) What happens when zinc sulphide is heated?

      (b) In a mixed oxide of metals the oxide ions, O2- forms hcp lattice. The divalent

       ions A2+ occupy 1/8 of the tetrahedral voids and the trivalent ions, B3+ ions occupy

      1/2 of the octahedral voids. Find formula of the compound.

  1. (a) Illustrate with a diagram the effect of concentration on molar conductivity of an electrolyte.

      (b) Calculate the e.m.f of the following cell at 298K:

      Cu(s)/Cu2+(0.01M) // Ce4+(0.05M)/ Ce3+(0.02M)

      E0Cu2+/Cu = 0.34 V, E0Ce4+/Ce3+ = 1.61 V

      State whether the e.m.f will increase or decrease if concentration of Ce4+ is



      (a) Calculate the degree of dissociation of 0.01 M NH4OH solution when its molar

conductivity is 9.4 W cm2 mol-1. It is given that the limiting molar conductivities of

NaCl, NH4 OH and NaOH are 126, 130 and 217 W cm2 mol-1 respectively.


  1. (a) Explain how [PtCl2 (NH3)2] and [Pt(NH3)6]Cl2 will differ in their electrolytic conductivity. Give the state of hybridization of Pt in these compounds.

(b) Though CO is a weak Lewis base yet it forms a number of stable metal cabonyls.Explain.

  1. (a)What are the advantages of liquid propellants over solid propellants?

(b) Name two examples of antiseptic dyes.

(c) Write one example each of cationic and anionic detergents.

  1. (a) Give reasons:

(i) H2+ ion is more stable than He2+ ion.

(ii)NF3 and BF3 are not isostructural.

(b) The sodium flame test has a characteristic yellow colour due to emission of wavelength 589 nm. What is

the mass equivalence of one photon of this wavelength?

  1.  Poly ethylene oxide is a synthetic polymer whose formula is HO (CH2CH2O)nH,

where “n” is a large integer. You prepare a sample of this polymer for which n

=180. Calculate the freezing point depression and the osmotic pressure at 293K of a

solution of 150mg of the polymer in 5.0ml of water and comment on the utility of

the two results in characterizing the polymer.

Kf for water=1.86 Kkgmol-1

R=0.082LAtmK-1mol-1. Volume of polyethylene oxide solution = 5.1 ml.

  1. (a) Calculate the Gibbs energy change and equilibrium constant for the following reaction at 298 K.

SO2 (g) + 2 H2S (g) ———————–à 3 S(s) + 2 H2O (l)

Df G of SO2 = -300.19 KJ/mol, Df G of H2S = -33.56 KJ/mol,

Df G of H2O = -237.13 KJ/mol. R= 8.314 JK-1mol-1.

(b) Write the most favourable circumstances for a spontaneous change.

  1.  The following rare data were obtained at 303 K for the following reaction:

2A +  B ———————– C  +  D     

 Experiment  | A |



 | B |


 Initial rate of formation of D

Mol L-1S-1










5.0 x 10-36.0 x 10-2

2.4 x 10-1

2.0 x 10-2


What is the rate law? Find the rate of the reaction when | A | =0.5 mol L-1 &

| B | = 0.2 mol L-1.

  1. (a)Account for the following:

(i)o-Nitro phenol is steam volatile while p-nitro phenol is not.

(ii) An aqueous solution of methylamine reacts with ferric    chloride to obtain

brown precipitate of ferric hydroxide.

(b) Write an example of Hoffmann bromamide reaction.

  1. (a) Name the chief ore of tin. Explain the process of extraction of tin from this ore.

      (b) Account for the following:

(a)Among the noble gases , only xenon is known to form chemical compounds.

(b)Ionization energy of Gallium is less than that of aluminium.

      (b) Complete and balance the following equation:

      XeF6  + H2O ——————-à



      (a) Draw the molecular shape of: (i) XeF4 (ii) Peroxomonosulphuric acid

      (b) Define catenation and illustrate it with reference to sulphur chemistry.

      (c) Write chemical equations for the commercial preparation of HI

  1. (a) For some of the first row transition elements the Eo values are:

      Element           V            Cr          Mn         Fe        Co             Ni        Cu       


      Eo (M2+/M)       -1.18       -0.91      -1.18      -0.44    -0.28        -0.25    +0.34

      In Volts

      `Give suitable explanation for the irregular trend in these values.

      (b) Give reasons for the following features of transition metal chemistry:

      (i)Transition metals exhibit higher oxidation state only in their oxides and fluorides.

      (ii)Transition metals have high enthalpy of atomization.

      (iii)The ionic radii of tripositive ions of lanthanide elements show a steady decrease

      from La3+ to Lu3+.


      (a) Explain the preparation of potassium permanganate from pyrolusite ore.

      (b) How does potassium dichromate react with acidified oxalic acid solution? Write

        balanced equation.

      (c) Explain with suitable example the use of a transition metal as a catalyst.

  1. An organic compound ‘A” having molecular formula C7H8O, does not react

      with sodium metal. When A is treated with HI, two compounds B and C are

      formed. Compound B reacts with sodium metal and also forms salt with NaOH.  B

      can be brominated and the major product contains three Br atoms. Compound C

      containing iodine reacts with Mg in dry ether to form Grignard reagent. The

      Grignard Reagent  reacts with CO2 followed by acid hydrolysis to form acetic acid.

      Identify A, B & C. Show the reactions involved.  

      (b) How are the following distinguished?

      (i)Ethanoyl chloride &  Ethanoic acid (ii) Nitrobenzene and benzonitrile


      (a) Write the mechanism of a reaction between a carboxylic acid and an alcohol in

       acid medium.

(b)Give comparative account of the following towards nucleophiles:


     (b)Identify the compounds and reagents:

     (A)    NaOH/Br2à     (B)    CHCl3/ KOH/ Heat à  (C)          (D) à      CH3 NH CH3

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