12th Chemistry Paper Solutions Set 3 : CBSE All India Previous Year 2012

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 are n-types semiconductors?


Answer :

The semiconductor whose increased conductivity is a result of negatively-charged electrons is called an n-type semiconductor. These are generated when the crystal of a group 14 element such as Si or Ge is doped with a group 15 element such as P or As.

Q2 :

Define “peptization”™.


Answer :

Peptization is the process of conversion of a precipitate into a colloidal sol by shaking it with the dispersion medium in the presence of an electrolyte. The electrolyte used in this reaction is known as a peptizing agent.

Q3 :

How is copper extracted from a low grade ore of it?


Answer :

Copper is extracted by hydrometallurgy from low grade ores.

Q4 :

What is the basicity of H3PO2 acid and why?


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Q5 :

Write the IUPAC name of the following.


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Q6 :

Write the IUPAC name of the following.


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Q7 :

Write a reaction which shows that all the carbon atoms in glucose are linked in a straight chain.


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Q8 :

What is the cause of a feeling of depression in human beings? Name a drug which can be useful in treating this depression.


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Q9 :

A reaction is of second order with respect to a reactant. How is its rate affected if the concentration of the reactant is (i) doubled (ii) reduced to half?


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Q10 :

Express the relation among cell constant, resistance of the solution in the cell and conductivity of the solution. How is molar conductivity of a solution related to its conductivity?

OR

The molar conductivity of a 1.5 M solution of an electrolyte is found to be 138.9S cm2 mol−1.

Calculate the conductivity of the conductivity of this solution.


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Q11 :

Explain the role of each of the following:

(i) NaCN in the extraction of silver

(ii) SiO2 in the extraction of copper


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Q12 :

Complete the following chemical equations:

(i)

(ii)


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Q13 :

Explain the following facts giving appropriate reason in each case:

(i) NF3 is an exothermic compound whereas NCl3 is not.

(ii) All the bonds in SF4 are not equivalen.


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Q14 :

Explain the following behaviours:

(i) Alcohols are more soluble in water than the hydrocarbons of comparable molecular masses.

(ii) Ortho-nitrophenol is more acidic than ortho-methoxyphenol.


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Q15 :

Explain the mechanism of acid catalysed hydration of an alkene to form corresponding alcohol.


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Q16 :

Complete the following chemical reaction equations:

(i) C6H5N2Cl + H3PO2+ H2O

(ii) C6H5NH2+ Br2(aq.)


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Q17 :

Describe the following giving the relevant chemical equation in each case:

(i) Carbylamine reaction

(ii) Hofmann”™s bromamide reaction.


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Q18 :

Differentiate between disinfectants and antiseptics. Give one example of each group.


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Q19 :

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 = 6.02 × 1023 mol−1)

OR

Iron has a body centred cubic unit cell with the cell dimension of 286.65 pm. Density of iron is 7.87 g cm−3. Use this information to calculate Avogadro”™s number. (Atomic mass of Fe = 56.0 u)


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Q20 :

The reaction N2(g) + O2(g) 2NO(g), contributes to air pollution whenever a fuel is burnt in air at a high temperature. At 1500 K, equilibrium constant K for it is 1.0 x 10-5. Suppose in a case [N2] = 0.80 mol L-1 and [O2] = 0.20 mol L-1 before any reaction occurs. Calculate the equilibrium concentrations of the reactants and the product after the mixture has been heated to 1500 K.


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Q21 :

The electrical resistance of a column of 0.05 M NaOH solution of diameter 1cm and length 50

cm is 5.55 × 103 ohm. Calculate its resistivity, conductivity and molar conductivity.


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Q22 :

Write three distinct features of chemisorptions which are not found in physisorptions.


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Q23 :

Explain each of the following observations:

(i) With the same d-orbital configuration (d4), Cr2+ is a reducing agent while Mn3+ is an oxidising agent.

(ii) Actinoids exhibit a much larger number of oxidation states than the lanthanoids.

(iii) There is hardly any increase in atomic size with increasing atomic number in a series of transition metals.


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Q24 :

Name of the following coordination entities and describe their structure:

(i) [Fe(CN)6]4−

(ii) [Cr(NH3)4Cl2]+

(iii) [Ni(CN)4]2−

(Atomic numbers Fe = 26. Cr = 24, Ni = 28)


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Q25 :

Answer the following question:

(i) What is meant by chirality of a compound? Give an example.

(ii) Which one of the following compounds is more easily hydrolyzed by KOH and why?

CH3CHCICH2CH3 or CH3CH2CH2Cl

(iii) Which one undergoes S N 2 substitution reaction faster and why?


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Q26 :

Define the following as related to proteins:

(i) Peptide linkage

(ii) Primary structure

(iii) Denaturation


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Q27 :

Differentiate between thermoplastic and thermosetting polymers. Give one example of each.


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Q28 :

(a) Draw the molecular structure of the following compounds.

(i) N2O5

(ii) XeOF4

(b) Explain the following observation:

(i) Sulphur has a greater tendency for catenation than oxygen.

(ii) ICI is more reactive than I2.

(iii) Despite lower value of its electron gain enthalpy with negative sign, fluorine (F2) is a stronger oxidizing agent than Cl2.

OR

(a) Complete the following chemical equation

(i) Cu + HNO3 (dilute) →

(ii) XeF4 + O2F2

(b) Explain the following observation:

(i) Phosphorus has greater tendency for catenation than nitrogen.

(ii) Oxygen is a gas but sulphur a solid.

(iii) The halogens are coloured. Why?


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Q29 :

(a) Write a suitable chemical equation to complete each of the following transformations:

(i) Butan-1-ol to butanoic acid

(ii) 4-methylacetophenone to benzene-1, 4-dicarboxylic acid

(b) An organic compound with molecular formula C9H10O forms 2,4-DNP derivative, reduces Tollen”™s reagent and undergoes Cannizzaro”™s reaction. On vigorous oxidation it gives 1, 2-benzenedicarboxylic acid. Identify the compound.

OR

(a) Give chemical tests to distinguish between

(i) Propanol and propanone

(ii) Benzaldehyde and acetophenone

(b) Arrange the following compounds in an increasing order of their property as indicated:

(i) Acetaldeyde, Acetone, Methyl tert-butyl ketone (reactivity towards HCN)

(ii) Benzoic acid, 3,4-Dinitrobenzoic acid, 4-Methoxybenzoic acid (acid strength).

(iii) CH3CH2CH(Br) COOH, CH3CH (Br) CH2COOH, (CH3)2CHCOOH (acid strength)


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Q30 :

(a) Define the following terms:

(i) Mole fraction

(ii) Ideal solution

(b) 15.0 g of an unknown molecular material is dissolved in 450 g of water. The resulting solution freezes at − 0.34°C. What is the molar mass of the material? (Kf for water = 1.86 K kg mol− 1)

OR

(a) Explain the following:

(i) Henry”™s law about dissolution of a gas in a liquid.

(ii) Boiling point elevation constant for a solvent.

(b) A solution of glycerol (C3H8O3) in water was prepared by dissolving some glycerol in 500 g of water. This solution has a boiling point of 100.42° C. What mass if glycerol was dissolved to make this solution? (Kb for water = 0.512 K kg mol−1)


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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.