Chemistry 2005 Set 1 Sol

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					2/4/2011                                         Subjective Test Paper - Chemistry - Meri…




  Chemistry 2005 Set 1                                                                           Close


 Subjective Test




      (i)    All questions are compulsory.
     (ii)    This question paper consists of four sections A, B, C and D.
              Section A contains 5 questions of one mark each.
              Section B is of 7 questions of two marks each.
              Section C is of 12 questions of three marks each and
              Section D is of 3 questions of five marks each.
     (iii)   There is no overall choice. However, an internal choice has been provided.
     (iv)    Wherever necessary, the diagrams drawn should be neat and properly labelled.



   Section A


    Question 1 ( 1.0 marks)
   What is the maximum possible coordination number of an atom in an hcp crystal structure of an
   element?

   Solution:
   The maximum possible coordination number of an atom in an hcp crystal structure of an element is
   12.



    Question 2 ( 1.0 marks)
   State the formula relating pressure of a gas with its mole fraction in a liquid solution in contact with
   it.

   Solution:
   The required formula is

   p = KHx

   Where,

   p → Partial pressure of the gas in vapour phase

   x → Mole fraction of the gas in solution

   KH → Henry’s constant



    Question 3 ( 1.0 marks)
   Express the relation between the half-life period of a reactant and its initial concentration if the
   reaction involved is of second order.

   Solution:




   Where,

      → Half life


   [R]0 → Initial concentration of reactant

   k → Rate constant



   Question 4 ( 1.0 marks)
…meritnation.com/…/t1IkDrsDbv5Aox5v…                                                                          1/14
2/4/2011
    Question 4 ( 1.0 marks)                          Subjective Test Paper - Chemistry - Meri…

   How are formalin and trioxane related to methanal?

   Solution:
   Formalin is a saturated solution of methanal in water (about 40% or 37% by mass).

   Trioxane (C 3 H6 O 3 ) is a cyclic trimer of methanal.




    Question 5 ( 1.0 marks)
   Why are primary amines higher boiling than tertiary amines?

   Solution:
   Primary amines undergo intermolecular H bonding, and hence, intermolecular association. However,
   intermolecular H bonding is absent from tertiary amines. So, they do not undergo intermolecular
   association. Hence, primary amines are higher boiling than tertiary amines.




   Section B


    Question 6 ( 2.0 marks)
   Show that the Heisenberg Uncertainty Principle is of negligible significance for an object of 10 −6 kg

   mass.


   OR

   On the basis of the Heisenberg Uncertainty Principle show that the electron (mass = 9 × 10−31 kg)
   cannot exist within an atomic nucleus of radius 10−15 m.

   Solution:
   According to the Heisenberg Uncertainty Principle,




   Given,

   m = 10 −6 kg




   We have observed that the value of ∆v. ∆x is extremely small and negligible. Therefore, we can say
   that the Heisenberg Uncertainty Principle is of negligible significance for an object of 10 −6 kg mass.

   Or

   According to the Heisenberg Uncertainty Principle,


…meritnation.com/…/t1IkDrsDbv5Aox5v…                                                                         2/14
2/4/2011                                         Subjective Test Paper - Chemistry - Meri…




   Here,

   m = 9 × 10−31 kg

   ∆x = 10 −15 m

   h = 6.6 × 10 −34 kg m2 s −1




   The value of ∆v is much higher than the velocity of light, so it is not possible. Hence, the electron
   cannot exist in the nucleus.



    Question 7 ( 2.0 marks)
   On the basis of the following     G ° values at 1073 K:




   Show that the roasting of zinc sulphide to form zinc oxide is a spontaneous process.

   Solution:
   The reaction involved in the roasting of zinc sulphide to form zinc oxide is




   Given,

                                                      … (i)


                                                       … (ii)


                                                     … (iii)

   Now, on adding equations (i) and (ii), and then subtracting the result by equation (iii), we have




   Since       for the process of roasting of ZnS to form ZnO is negative, it is a spontaneous process.



    Question 8 ( 2.0 marks)
   Write one chemical reaction each to show that

   (a) Tin (II) chloride is a reducing agent.

   (b) Chlorine gas can be obtained from bleaching powder.

   Solution:
   (a) Out of current syllabus

   (b) Out of current syllabus



…meritnation.com/…/t1IkDrsDbv5Aox5v…                                                                       3/14
2/4/2011                                        Subjective Test Paper - Chemistry - Meri…
    Question     9 ( 2.0 marks)
   Describe the steps involved in the preparation of either potassium dichromate from sodium chromate
   or potassium permanganate from manganese dioxide.

   Solution:
   Sodium chromate is acidified with sulphuric acid to give sodium dichromate, which on further
   treatment with potassium chloride yields potassium dichromate.




   OR

   Manganese dioxide is fused with an alkali metal hydroxide and an oxidising agent like KNO 3 to
   produce potassium manganate, which disproportionates in a neutral or acidic solution to give
   potassium permanganate.




    Question 10 ( 2.0 marks)
   What are enantiomers and diastereomers? Differentiate between chiral and achiral molecules.

   Solution:
   Enantiomers are mirror images that cannot be superimposed on one another. Diastereomers are
   stereoisomers that are not mirror images of each other.

   Chiral molecules are the molecules which cannot be superimposed upon their mirror images. On the
   other hand, achiral molecules are the molecules which can be superimposed upon their mirror
   images.



    Question 11 ( 2.0 marks)
   Give an illustration of Reimer−Teimann reaction.

   Solution:
   When phenol is treated with chloroform in the presence of sodium hydroxide, a −CHO group is
   introduced at the ortho position of benzene ring, leading to the formation of a substituted benzal
   chloride as the intermediate. On hydrolysis, this intermediate, in the presence of an alkali, gives
   salicylaldehyde.

   This reaction is known as Reimer−Teimann reaction.




    Question 12 ( 2.0 marks)
   How is bakelite made and what is its major use? Why is bakelite a thermo-setting polymer?

   Solution:
   Bakelite is made by the co-polymerisation of phenol and formaldehyde.


…meritnation.com/…/t1IkDrsDbv5Aox5v…                                                                     4/14
2/4/2011                                         Subjective Test Paper - Chemistry - Meri…




   Bakelite is used for making combs, electrical switches, handles of utensils, computer discs, etc.

   When moulded once, bakelite cannot be softened on heating. So, it is a thermosetting plastic.



   Section C


    Question 13 ( 3.0 marks)
   (a) What is meant by linear combination of atomic orbitals?

   (b) Illustrate bonding and anti-bonding molecular orbitals based on homo-nuclear dihydrogen
   molecule.

   OR

   What kinds of molecular forces are expected to exist between the species in any three of the
   following pairs constituting mixtures?

   (a) He and N2

   (b) Cl2 and NO - 3

   (c) NH3 and CO 2

   (d) H2 S and HBr


   Solution:
   (a) Linear combination of atomic orbitals (LCAO) method is an approximate technique to obtain the
   wave functions for molecular orbitals.

   (b) Each hydrogen atom in ground state has one electron in is orbital. The atomic orbitals of these
   atoms can be represented by the wave functions Ψ A and Ψ B. Then, according to LCAO method, the
   molecular orbitals in the H2 molecule are given by the linear combination (addition or subtraction of
   wave functions of the individual atoms) of Ψ A and Ψ B as shown below.

   Ψ MO = Ψ A ± Ψ B

   Therefore, the two molecular orbitals σ and σ* are formed as

   σ = ΨA + ΨB

   σ* = Ψ A − Ψ B

   σ is called bonding molecular orbital as it is formed by the addition of atomic orbitals, and σ* is called
   anti-bonding molecular orbitals as it is formed by the subtraction of atomic orbitals.




   OR

   (a) He and N2 → London force

   (b) Cl2 and NO - 3 → Ion-induced dipole

   (c) NH3 and CO 2 → Dipole−dipole force

   (d) H2 S and HBr → Hydrogen bond



    Question 14 ( 3.0 marks)

…meritnation.com/…/t1IkDrsDbv5Aox5v…                                                                            5/14
2/4/2011                                          Subjective Test Paper - Chemistry - Meri…
   Aluminium metal forms a cubic close-packed crystal structure. Its atomic radius is 125 x 10 -12 m.

   (a) Calculate the length of the side of the unit cell.

   (b) How many such unit cells are there in 1.00 m3 of aluminium?

   Solution:
   (a) For a cubic close-packed crystal structure,


   Radius of an atom,


   Where, a → Edge length

   Therefore, a =




   Hence, the length of the side of the unit cell is 354 × 10 −12 m.

   (b) Volume of the unit cell = a3




    Question 15 ( 3.0 marks)
   A solution is made by dissolving 30 g of a non-volatile solute in 90 g of water. It has a vapour
   pressure of 2.8 kPa at 298 K. At 298 K, vapour pressure of pure water is 3.64 kPa. Calculate the
   molar mass of the solute.

   Solution:
   Given,

   Vapour pressure of pure water at 298 K, p° = 3.64 kPa

   Vapour pressure of the solution at 298 K, p = 2.8 kPa

   Mass of the solute = 30 g

   Mass of water = 90 g


   Now, moles of water =               = 5 mol


   Let molar mass of the solute be M.


   So, moles of solute =




   Now, mole fraction of w ater,




   We know that




…meritnation.com/…/t1IkDrsDbv5Aox5v…                                                                    6/14
2/4/2011                                          Subjective Test Paper - Chemistry - Meri…




   Hence, molar mass of the solute is 20 g mole −1 .



    Question 16 ( 3.0 marks)
   Comment on the validity of the following statements, giving reasons:

   (a) Thermodynamically an exothermic reaction is sometimes not spontaneous.

   (b) The entropy of steam is more than that of water at its boiling point.

   (c) The equilibrium constant for a reaction is one or more if ∆rG0 for it is less than zero.


   Solution:
   (a) For a spontaneous reaction, ∆G < 0

   We know that

   ∆G = ∆H − T∆S

   For an exothermic reaction, ∆H < 0

   An exothermic reaction will be non-spontaneous if an only if the change in entropy (∆S) is highly
   negative to make T∆S positive and greater in magnitude than ∆H. This will make ∆G positive and
   non-spontaneous.

   (b) Entropy is the measure of the degree of randomness or disorder in a system, i.e., decrease in
   regularity in structure means increase in entropy. Steam is more disordered in structure than water.
   Therefore, the entropy of steam is more than that of water at its boiling point.

   (c) For ∆r G0 < 0, the reaction is spontaneous. For a spontaneous reaction, the value of equilibrium
   constant (K) is greater than 1. This is why a reaction with ∆r G0 les than zero always has an
   equilibrium constant value greater than 1.

   Mathematically,


   K=

   If ∆G0 < 0,

   Then −∆G0 /RT > O

   So,

   Therefore, K > 1



    Question 17 ( 3.0 marks)
   A first-order reaction takes 69.3 minutes for 50% completion. Set up an equation for determining the
   time needed for 80% completion of this reaction. (Calculation of result is not required)

   Solution:

   Given,


   For a first-order reaction,




…meritnation.com/…/t1IkDrsDbv5Aox5v…                                                                      7/14
2/4/2011                                          Subjective Test Paper - Chemistry - Meri…



   Hence, the required time for 80% completion of the reaction is 161 minutes approximately.



    Question 18 ( 3.0 marks)
   Illustrate with examples:

   (a) Lyophilic and Lyophobic sols

   (b) Multimolecular and Macromolecular colloids

   (c) Homogeneous and Heterogeneous catalysis

   Solution:
   (a) Lyophilic sols are colloidal sols formed by bringing substances such as gum, gelatin, starch,
   rubber, etc., in contact with the solvent.

   Substances such as metals, their sulphides, etc., do not from colloidal sols when simply mixed with
   the dispersion medium. Their colloidal sols can be prepared only by special methods. Such sols are
   called lyophobic sols.

   (b) Multimolecular colloids are the species having size in the colloidal range (diameter < 1 nm). They
   are formed by the aggregation of a large number of atoms or smaller molecules of a substance on
   dilution, e.g., sulphur sol; it consists of particles containing a thousand or more of S8 molecules.

   Macromolecular colloids are the species in which the dispersed particles are large molecules, usually
   polymers. The sizes of these particles lie within the colloidal range. Thus, their dispersions behave
   like colloidal solutions, e.g., synthetic rubber.

   (c) The reaction in which the catalyst is present in the same phase as the reactants is said to be
   homogeneous catalysis. For example: the oxidation of sulphur dioxide into sulphur trioxide in the
   presence of oxides of nitrogen in a lead chamber.




   The catalytic process in which the reactants and catalyst are present in different phases is said to be
   heterogeneous catalysis. For example: the oxidation of sulphur dioxide into sulphur trioxide in the
   presence of Pt.




    Question 19 ( 3.0 marks)
   The E° values in respect of electrodes of chromium (Z = 24), manganese (Z = 25) and iron (Z =26)
   are:




   On the basis of the above information compare the feasibilities of further oxidation of their +2
   oxidation states.

   Solution:
   From the given data, it is known that the +2 oxidation state of Mn is more stable than that of Fe,
   which in turn is more stable than that of Cr. Therefore, further oxidation of the +0 oxidation state of
   Cr is more feasible than that of Fe, which in turn is more feasible than that of Mn, i.e., the order of
   the feasibilities of the further oxidation of the +2 oxidation state is:




    Question 20 ( 3.0 marks)
   Draw a sketch to show the splitting of d orbitals in an octahedral crystal field. State for a d6 ion how
   the actual configuration of the split d orbitals in an octahedral crystal field is decided by the relative
   values of ∆0 and P.


   Solution:




…meritnation.com/…/t1IkDrsDbv5Aox5v…                                                                            8/14
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   For a d6 ion, if ∆0 < P, then the first three electrons enter the     orbital; the fourth and fifth

   electrons enter the      orbital; and the sixth electron enters the     orbital, giving the configuration

           .


   On the other hand, if ∆0 > P, then all the six electrons enter the      orbital, giving the configuration

           .



    Question 21 ( 3.0 marks)
   (a) Write the structural formula of 3-phenylprop-2-enal.

   (b) Write one chemical equation each to illustrate the following reactions:

   (i) Aldol condensation

   (ii) Cannizzaro's reaction

   Solution:
   (a)




   (b) (i) Aldol condensation




   (ii) Cannizzaro’s reaction




    Question 22 ( 3.0 marks)
   (a) Assign a reason for each of the following statements:

   (i) Alkylamines are stronger bases than arylamines.

   (ii) Acetonitrile is preferred as solvent for carrying out several organic reactions.

   (b) How would you convert methylamine into ethylamine?

   Solution:
   (a) (i) In arylamines, due to resonance in the benzene ring, the lone pair of electrons on the nitrogen
   atom is less available for donation. Hence, alkylamines are stronger bases than arylamines.




   (ii) The reasons for which acetonitrile is preferred as a solvent for carrying out several organic
   reactions are given below.
…meritnation.com/…/t1IkDrsDbv5Aox5v…                                                                           9/14
2/4/2011
    reactions   are given below.                     Subjective Test Paper - Chemistry - Meri…
    1. Due to its high polar nature, it can dissolve a variety of reactants.

    2. It does not react with mild acidic and basic substances.

    3. It is miscible with water and a variety of organic solvents.

    4. The boiling point of acetone is moderate, so it can be easily removed.

    (b)




     Question 23 ( 3.0 marks)
    When the nuclides        ,       and          are separately subjected to (α, n) nuclear reactions, three
    separate new nuclides are produced, each of which further undergoes one positron emission, finally
    giving stable nuclei. Write the nuclear equations for the reactions involved in these cases.

    Solution:
    Out of current syllabus



     Question 24 ( 3.0 marks)
    (a) State the function along with one example each of:

    (i) Antihistamines

    (ii) Antioxidants

    (b) What are hybrid propellants?

    Solution:
    (a) (i) Antihistamines: The function of antihistamines is to relieve the symptoms of allergies caused
    by histamines (a compound made from amino acid histidine), e.g., brompheniramine (Dimetapp).

    (ii) Antioxidants: The function of antioxidants is to prevent oxidation of other molecules, and thereby,
    retard the formation of free radicals, e.g., glutathione.

    (b) Out of current syllabus



    Section D


     Question 25 ( 5.0 marks)
    (a) Define electrical conductivity and molar conductivity of a solution and write the units of molar
    conductivity.

    (b) The E° values corresponding to the following two reduction electrode processes are:

    (i)

    (ii)

    Formulate the galvanic cell for their combination. What will be the standard cell potential for it?
    Calculate      for the cell reaction. (F = 96500 C mol -1 ) (2, 3)

    OR

    (a) In the button cell, widely used in watches and other devices, the following reaction takes place:




    Determine E° and          for the reaction.


    Given

    (b) Explain with examples the terms weak and strong electrolytes. How can these be distinguished?
…meritnation.com/…/t1IkDrsDbv5Aox5v…                                                                            10/14
2/4/2011                                         Subjective Test Paper - Chemistry - Meri…
   (b) Explain with examples the terms weak and strong electrolytes. How can these be distinguished?

   Solution:
   (a) Electrical conductivity of a solution is the conductance of the solution enclosed in a cell containing
   two electrodes having unit cross-sectional area and separated by one cm.

   Molar conductivity of a solution at a given concentration is the conductance of volume V of the
   solution containing 1 mole of the electrolyte kept between two electrodes having the area of cross-
   section A and separated by a distance of unit length.




   Now, l = 1 and A = V (Volume containing 1 mole of the electrolyte)

   So,

   Unit of molar conductivity is S m2 mol−1 or S cm2 mol−1 .

   (b) The galvanic cell representation is

   Cu +|Cu 2+||Cu +|Cu

   The standard cell potential is




   We know that




   Here,

   n =1

   F = 96500 C mol−1

   So,


   = − 34740 J mol−1

   OR

   (a) From the given reaction, it is known that zinc is oxidised and silver is reduced in the button cell.

   The reactions occurring at the anode and cathode are −

   Anode:


   Cathode:




   We know that




   Here,

   n =2

   F = 96500 C mol−1




   (b) Strong electrolytes are substances which dissociate completely (100%) in solution. Strong acids
   (such as HCl, HNO 3 ), strong bases (such as NaOH, KOH) and salts that are not weak acids or weak
   bases (such as NaCl, KBr) are strong electrolytes.

   Weak electrolytes are substances which dissociate partially in solution. Weak acids (such as CH
…meritnation.com/…/t1IkDrsDbv5Aox5v…                                                                            11/14
2/4/2011                                           Subjective Test Paper - Chemistry - Meri…
   Weak electrolytes are substances which dissociate partially in solution. Weak acids (such as CH3
   COOH3 C 5 H5 N) are weak electrolytes.

   Strong and weak electrolytes can be distinguished by their conducting power, which is expressed in
   terms of degree of dissociation. For strong electrolytes, it is almost equal to 1, while for weak
   electrolytes, its value is less than 1.



    Question 26 ( 5.0 marks)
   (a) Assign an appropriate reason for each of the following statements:

   (i)        is known but         is not known.

   (ii) More metal fluorides are ionic in nature than metal chlorides.

   (iii) Solid phosphorus pentachloride exhibits some ionic character.

   (b) Write the structural formulae for the following:

   (i) BrF3

   (ii) XeOF4

   OR

   (a) Assign a reason for each of the following:

   (i) In group 14 the tendency for catenation decreases with increasing atomic numbers.

   (ii) In group 15 the bond angle H - M - H decreases in the following order

   NH3 (107.8°), PH3 (93.6°), AsH3 (91.8°)

   (iii) Sulphur hexafluoride is used as a gaseous electrical insulator.

   (b) Complete the follow ing reaction equations:

   (i) R2 SiCI2 + H2 O

   (ii) XeF4 + H2 O


   Solution:
   (a) (i) The reasons for which         is known but          is not known are −

   1. Due to the large size of chloride ions, six chloride ions cannot be accommodated around         ion.

   2. The interaction between Si4+ and lone pair of Cl− ion is weak.

   (ii) Fluorine is more electronegative than chlorine. So, fluorine tends to form more ionic compounds
   than chlorine. Hence, more metal fluorides are ionic in nature than chlorine.

   (iii) In solid state, phosphorus pentachloride (PCl5 ) exists as                 .So, solid phosphorus

   pentachloride exhibits some ionic character. The cation            has tetrahedral structure and the

   anion           has octahedral structure.

   (b) (i)




   (ii)




…meritnation.com/…/t1IkDrsDbv5Aox5v…                                                                         12/14
2/4/2011                                         Subjective Test Paper - Chemistry - Meri…
   OR

   (a) (i) On moving down a group, atomic size increases and electronegativity decreases. This is why in
   group 14, the tendency for catenation decreases with increasing atomic numbers.

   (ii) The greater the electronegativity, the higher is the electron density around the atom. As a result,
   the repulsion between the electron pairs is higher, and consequently, the H−M−H angle is greater.

   Electronegativity increases in the order

   As < P < N

   Thus, the bond angle H−M−H decreases in the order

   H−N−H < H−P−H < H−As−H

   (iii) Sulphur hexafluoride (SF6 ) is exceptionally stable due to steric reasons. It is used as a gaseous
   electrical insulator in gas-filled high voltage insulators as it can suppress internal discharges.

   (b) (i)




   (ii)



    Question 27 ( 5.0 marks)
   (a) Write chemical equations for the reactions of glucose with

   (i) acetic anhydride and

   (ii) ammoniacal silver nitrate solution.

   (b) Draw simple Fischer projections of D-glucose and L-glucose.

   (c) What do you understand by replication by DNA? How does DNA differ from RNA structurally?

   OR

   (a) Write the following about protein synthesis:

   (i) Name the location where protein synthesis occurs.

   (ii) How do 64 codons code for only 20 amino acids?

   (iii) Which of the two bases of the codon are most important for coding?

   (b) What deficiency diseases are caused due to lack of vitamins A, B, B6 and K in human diet?


   Solution:
   (a) (i)




   (ii)




   (b)




…meritnation.com/…/t1IkDrsDbv5Aox5v…                                                                          13/14
2/4/2011                                        Subjective Test Paper - Chemistry - Meri…




   (c) Replication of DNA refers to a fundamental process occurring in all living organisms in which a
   single DNA molecule produces two identical copies of itself during cell division.

   Structural difference between DNA and RNA:

   (i) The sugar moiety in DNA is β−D−2−deoxyribose, whereas that in RNA is β−D−ribose.

   (ii) DNA contains the base thymine. RNA contains the base uracil.

   (iii) DNA is double stranded, whereas RNA is single stranded.

   OR

   (a) Out of current syllabus

   (b)

           Name of vitamin                             Deficiency diseases

               Vitamin A       Xerophthalmia (hardening of the cornea of the eye), night blindness

              Vitamin B1                    Beriberi (appetite loss, growth retardation)

              Vitamin B6                                    Convulsions

               Vitamin K                             Delaying of blood clotting




…meritnation.com/…/t1IkDrsDbv5Aox5v…                                                                     14/14

				
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