CBSE Sample Papers for Class 12 Chemistry Solved 2016 Set 12

Section A

1.Name the type of potential difference produced between the fixed charged layer and diffused layer having opposite charges around the colloidal particle.

2.Write the IUPAC name of the compound (CH3 )3CCH2COOH.

3. Which stoichiometric defect increases the density of a solid?
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Section B

6.(i) Based on solute-solvent interactions, arrange the following in the increasing order  of solubility in n-octane.

Cyclohexane, KC1, CH3 OH, CH3 CN

(ii) What do you mean by saturated solution?

7. (i) Cobalt(III) is stable in aqueous solution but in the presence of complexing  reagents, it is easily oxidised.

(ii) In the series, Sc(Z = 21) to Zn(Z = 30), the enthalpy of atomisation of zinc is the lowest, i.e. 126 kJ mol-1. Why?

8. Resistance of a conductivity cell filled with 0.1 mol L_1 KC1 solution is 100 Q. If the  resistance of the same cell when filled with 0.02 mol L-1 KC1 solution is 5200, calculate the conductivity and molar conductivity of 0.02 mol L-1 KC1 solution. The conductivity of 0.1 mol L_1 KC1 solution is 1.29 S/m.

9.Convert:

  • 3-methylaniline into 3-nitrotoluene.
  • aniline into 1,3,5-tribromobenzene.

Or

Account for the following:

  • In aromatic electrophilic substitution, although amino group are opposite directing but aniline on nitration gives a substantial amount of m-nitroaniline.
  • Diazonium salts of aromatic amines are more stable than that of aliphatic amines.

10.Synthesise benzylamine (PhCH2NH2) by

  • reductive amination.
  • nitrile reduction.

Section C

11. (i) Interhalogens are more reactive than halogens. Why?

(ii) Give chemical reactions in support of the following observations.

(a) Sulphuric acid has low volatility.

 

(b) Iodide ions can be oxidised by oxygen in acidic medium.

12. (i) Write two characteristics of barbiturates.

(ii) Discuss the two ways in which drugs can prevent the attachment of natural substrate on active site of an enzyme.

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15. Copper crystallises with face centred cubic unit cell. If the radius of copper atom is 127.8 pm, calculate the density of copper metal.

[Atomic mass of Cu = 63.55 u and Avogadro’s number NA = 6.02x 1023 mol-1]

or

Metallic gold crystallises in a face centred cubic lattice. The length (a) of the cubic unit cell is 4.070 A. (Atomic mass of gold =197u)

  • What is the closest distance between gold atoms?
  • How many “nearest neighbours” does each gold atom have at a distance calculated  in (i)?
  • What is the density of gold?

16. 2 g of benzoic acid (C6H5COOH) dissolved in 25 g of benzene shows a depression in freezing point equal to 1.62 K. Molar depression constant for benzene is 4.9 K kg mol-1. What is the percentage association of acid, if it forms dimer in solution.
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18.(i) Give one main difference between lyophilic and lyophobic colloids. (1)

(ii) Explain,

  • Sky appears blue in colour.
  • A freshly formed precipitate of ferric hydroxide can be converted into a colloidal  sol by shaking it with a small quantity of ferric chloride.

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20.What is the role of benzoyl peroxide in addition polymerisation of alkenes?

Explain its mode of action with the help of an example.

21.(i) State the hybridisation and magnetic behaviour of [Cr(CO)6 ].

[Atomic number of Cr is 24]

(ii) Which of the two K4 [Fe(CN)6 ] or K3 [Fe(CN)6 ] is more stable and why?

(iii) What are the various factors affecting crystal field splitting energy?

22.Describe how following changes are brought about?

  • Pig iron to steel
  • Pig iron to cast iron
  • Impure copper into pure copper

Section D

23. Humans, monkeys and guinea pigs do not have the enzymes necessary for the biosynthesis of vitamin C, so they must include the vitamin in their diets. It is also required for the synthesis of collagen, which is the structural protein of skin, tendors, connective tissue and bone.

Answer the following questions based on the above passage.

  • Give the structure of vitamin C and the functional groups therein.
  • Is it acidic in nature? What is the common name of vitamin C?
  • What values are associated with vitamin C?

Section E

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