12th Chemistry Paper Solutions Set 1 : CBSE Delhi Previous Year 2008

General Instructions:
(i) All questions are compulsory
(ii) Question numbers 1 to 8 are very short-answer questions and carry 1 mark each.
(iii) Question numbers 9 to 18 are short-answer questions and carry 2 marks each.
(iv) Question numbers 19 to 27 are also short-answer questions and carry 3 marks.
(v) Question numbers 28 to 30 are long-answer questions and carry 5 marks each.
(vi) Use Log Tables, if necessary. Use of calculators is not allowed.
Q1 :

What is the coordination number of each type of ions in a rock-salt type crystal structure?


Answer :

In rock salt or common salt, every Na+ion is surrounded by 6 Clions and each Cl ion is surrounded by 6 Na+ions. Thus, the coordination number of each type of ion in rock salt is 6.

Q2 :

Define the term “order of reaction”™ for chemical reactions.


Answer :

The sum of the powers of the concentrations of the reactants of a chemical reaction in the rate law expression is called the order of that chemical reaction.

Rate = k[A]x[B]y

Order of reaction = x+ y

Q3 :

What causes Brownian movement in a colloidal solution?


Answer :

The particles of a colloidal solution keep moving in a zigzag pattern. This happens because of unbalanced bombardment of the colloidal particles by the molecules of the dispersion medium.

(The particles of the dispersion medium keep striking the particles of the dispersion phase from all directions and with different force. This transfers the kinetic energy from the particles of the dispersion medium to the particles of the dispersion phase in a random manner. As the collisions are random in nature, the movement of the particles is also random.)

Q4 :

In which one of the two structures, and , the bond angle has a higher

value? 


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Q5 :

Write the IUPAC name of the following compound:


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Q6 :

Arrange the following compounds in an increasing order of their acid strengths:

(CH3)2CHCOOH, CH3CH2CH(Br)COOH, CH3CH(Br)CH2COOH


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Q7 :

Write a chemical reaction in which the iodide ion replaces the diazonium group in a diazonium salt.


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Q8 :

Name a substance that can be used as an antiseptic as well as a disinfectant.


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Q9 :

Explain as to why haloarenes are much less reactive than haloalkanes towards nucleophilic substitution reactions.

OR

Which compound in each of the following pairs will react faster in SN2 reaction with −OH? Why?

(i) CH3Br or CH3I

(ii) (CH3)3CCl or CH3Cl


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Q10 :

(a) State the IUPAC name of the following compound:

(b) Complete the following chemical equation:

CH3CH2CH=CH2+ HBr


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Q11 :

State Henry”™s law correlating the pressure of a gas and its solubility in a solvent and mention two applications for the law.


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Q12 :

A first order decomposition reaction takes 40 minutes for 30% decomposition. Calculate its value.


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Q13 :

What is meant by the “rate constant, k”™ of a reaction? If the concentration be expressed in mol L−1units and time in seconds, what would be the units for k (i) for a zero-order reaction and (ii) for a first-order reaction?


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Q14 :

Define the following terms in relation to proteins:

(i) Peptide linkage

(ii) Denaturation


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Q15 :

List the reactions of glucose which cannot be explained by its open-chain structure.


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Q16 :

Assign a reason for each of the following statements:

(i) Ammonia is a stronger base than phosphine.

(ii) Sulphur in vapour state exhibits a paramagnetic behaviour.


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Q17 :

Draw the structure of the following molecules:

(i) SF4

(ii) XeF4


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Q18 :

What are biodegradable and non-biodegradable detergents? Give one example of each class.


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Q19 :

What is semiconductor? Describe the two main types of semiconductors and explain mechanisms for their conduction.


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Q20 :

Calculate the temperature at which a solution containing 54g of glucose, (C6H12O6), in 250 g of water will freeze.

(Kffor water = 1.86 K mol−1kg)


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Q21 :

What are lyophilic and lyophobic sols? Give one example of each type. Which one of these two types of sols is easily coagulated and why?


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Q22 :

State briefly the principles which serve as basis for the following operations in metallurgy:

(i) Froth floatation process

(ii) Zone refining

(iii) Refining by liquation


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Q23 :

Write chemical equations for the following processes:

(i) Chlorine reacts with a hot concentrated solution of sodium hydroxide

(ii) Orthophosphorous acid is heated

(iii) PtF6and xenon are mixed together

OR

Complete the following chemical equations:

(i) Ca3P2(s) + H2O(l) →……..

(iii) F2(g) + H2O(l) →……..


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Q24 :

(a) What is a ligand? Give an example of a bidentate ligand.

(b) Explain as to 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)


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Q25 :

Name the reagents which are used in the following conversions:

(i) A primary alcohol to an aldehyde

(ii) Butan-2-one to butan-2-ol

(iii) Phenol to 2, 4, 6-tribromophenol


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Q26 :

Account for the following observations:

(i) pKbfor 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.


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Q27 :

Write the names and structures of the monomers of the following polymers:

(i) Buna-S

(ii) Neoprene

(iii) Nylon-6


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Q28 :

Conductivity of 0.00241 M acetic acid solution is 7.896 x 10-5S cm-1. Calculate its molar conductivity in this solution. If for acetic acid be 390.5 S cm2mol-1, what would be its dissociation constant?

OR

Three electrolytic cells A, B and C containing solutions of zinc sulphate, silver nitrate and copper sulphate respectively, are connected in series. A steady current of 1.5 ampere was passed through them until 1.45 g of silver was deposited at the cathode of cell B. How long did the current flow? What mass of copper and what mass of zinc were deposited in the concerned cells?

(Atomic masses of Ag = 108, Zn = 65.4, Cu = 63.5)


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Q29 :

Assign reasons for the following:

(i) The enthalpies of atomisation of transition elements are high.

(ii) The transition metals and many of their compounds act as good catalyst.

(iii) From element to element the actinoid contraction is greater than the lanthanoid contraction.

(iv) The E0value for the Mn3+/Mn2+couple is much more positive than that for Cr3+/Cr2+.

(v) Scandium (Z = 21) does not exhibit variable oxidation states and yet it is regarded as a transition element.

OR

(a) What may be the possible oxidation states of the transition metals with the following delectronic configurations in the ground state of their atoms:

3d34s2, 3d54s2and 3d64s2

Indicate relative stability of oxidation states in each case.

(b) Write steps involved in the preparation of (i) Na2CrO4from chromite ore and (ii) K2MnO4from pyrolusite ore.


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Q30 :

(a) Complete the following reaction statements by giving the missing starting material, reagent or product as required:

(i)

(ii)

(iii)

(b) Describe the following reactions:

(i) Cannizaro reaction

(ii) Cross aldol condensation

OR

(a) How would you account for the following:

(i) Aldehydes are more reactive than ketones towards nucleophiles.

(ii) The boiling points of aldehydes and ketones are lower than those of the corresponding acids.

  1. The aldehydes and ketones undergo a number of addition reactions.

(b) Give chemical tests to distinguish between:

(i) Acetaldehyde and benzaldehyde

(ii) Propanone and propanol


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12th Chemistry Paper Solutions Set 3 : CBSE Delhi Previous Year 2013 will be available online in PDF book soon. The solutions are absolutely Free. Soon you will be able to download the solutions.