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Board Paper of Class 12 2016 Chemistry - Solutions

Answer all questions in Part A and six questions from Part B choosing two questions from Section A, two from Section B and two from Section C.
All working, including rough work, should be done on the same sheet as, and adjacent to the rest of the answer.
The intended marks for questions or parts of questions are given in brackets [ ].
Balanced equations must be given wherever possible and diagrams where they are helpful.
When solving numerical problems, all essential working must be shown.
In working out problems, use the following data:
Gas constant R = 1·987 cal deg–1 mol–1 = 8·314 JK–1 mol–1 = 0·0821 dm3 atm K–1mol–1 1 l atm = 1 dm3 atm = 101·3 J. 1 Faraday = 96500 Coulombs.
Avogadro’s number = 6·023 × 1023

  • Question 1
    (a) Fill in the blanks by choosing the appropriate word/words from those given in the brackets:
    (Henry's, aldol condensation, absence, do not, ohm, Raoult's, increases, common ion effect, easily, three, solubility product, ohm–1, two, four, ohm–1cm2, cannizzaro, ohrn–1cm–1·', zero, decreases, presence).
    (i) Ideal solutions obey. __________ law and they __________ form azeotropic mixtures.
    (ii) Benzaldehyde undergoes __________ reaction due to __________ of α-hydrogen atom.
    (iii) The solubility of silver chloride __________ in the presence of sodium chloride because of __________
    (iv) The unit of conductance is __________ and that of specific conductance is __________
    (v) When the concentration of a reactant of first order reaction is doubled, the rate becomes ____ times, but for __________ order reaction, the rate remains same.

    (b) Complete the following statements by selecting the correct alternative from the choices given:
    (i) Electrochemical equivalent is the amount of substance which gets deposited from its solution on passing electrical charge equal to:
    (1) 96,500 Coulombs
    (2) 1 Coulomb
    (3) 60 Coulombs
    (4) 965 Coulombs

    (ii) The complex ion [Ni(CN)4]2– is:
    (1) Square planar and diamagnetic
    (2) Tetrahedral _and paramagnetic
    (3) Square planar and paramagnetic
    (4) Tetrahedral and diamagnetic

    (iii) Wohler's synthesis is used for the preparation of:
    (I) Glycine
    (2) Amino acids
    (3) Urea
    (4) Proteins

    (iv) When SO2 gas is passed through acidified K2Cr2O7 solution, the colour of the solution changes to:
    (1) Red
    (2) Black
    (3) Orange
    (4) Green

    (v) In the equation CH3COOH+Cl2-HClRed PA, the compound A is:
    (1) CH3CH2Cl
    (2) ClCH2COOH
    (3) CH3Cl
    (4) CH3COCl

    (c) Answer the following questions:
    (i) What is the order of reaction whose rate constant has the same unit as the rate of reaction?
    (ii)· What is the pH value of a solution whose hydroxyl ion concentration is 1 × 10–2 M?
    (iii) Calculate the number of coulombs required to deposit 5·4g of Al when the electrode reaction is:
    Al3+ + 3e →+ Al           [Atomic Weight of Al = 27 g / mol].
    (iv) Write the reaction to prepare acetaldehyde from hydrogen gas and an acid chloride.
    (v) The edge length of unit cell of a body centered cubic (bcc) crystal is 352 pm. Calculate the radius of the atom.

    (d) Match the following:
     (i) Weak electrolyte  (a) pH of a solution
     (ii) Colour in crystals  (b) Iodoform
     (iii) Acetone  (c) Tollen's reagent
     (iv) Sorensen  (d) Ostwald dilution law
     (v) Ammonical silver nitrate  (e) F - centre

  • Question 2
    (a) (i) A 10% aqueous solution of cane sugar (mol. wt. 342) is isotonic with 1·754% aqueous solution of urea. Find the molecular mass of urea.

    (ii) The molecular weight of an organic compound is 58 g mol–1. What will be the boiling point of a solution containing 48 grams of the solute in 1200 grams of water?
    [Kb for water = 0·513° C kg mole–1; Boiling point of water = 100°C.]

    (iii) What will be the value of Van't Hoff factor(i) of benzoic acid if it dimerises in aqueous solution?
     How will the experimental molecular weight vary as compared to the normal molecular weight?

    (b) (i) Determine the pH value of 0·001 M acetic acid solution if it is 2% ionised at this concentration.
    How can the degree of dissociation of this acetic acid solution be increased?

    (ii) The solubility product of PbCl2 at 298K is l.7 × 10–5. Calculate the solubility of PbCl2 in g/lit. at 298K.
    Atomic Weights: [Pb = 207 and Cl = 35·5]

    (c) Graphite is anisotropic with respect to conduction of electric current. Explain. VIEW SOLUTION

  • Question 3
    (a) (i) In a body centered and face centered arrangement of atoms of an element, what will be the number of atoms present in respective unit cells? Justify your answer with calculation.
    (ii) A compound AB has a simple cubic structure and has molecular mass 99. Its density is 3·4 g cm–3. What will be the edge length of the unit cell?

    (b) (i) For the reaction: 2NOgN2g+O2g; H=-heat Ke=2.5×102 at 298 K what will happen to the concentration of N2 if:
    (1) Temperature is decreased to 273K.
    (2) Pressure is reduced.

    (ii) In a first order reaction, 10% of the reactant is consumed in 25 minutes. Calculate:
    (1) The half-life period of the reaction.
    (2) The time required for completing 87·5% of the reaction.

    (c) Water acts as Bronsted acid as well as a Bronsted base. Give one example each to illustrate this statement. VIEW SOLUTION

  • Question 4
    (a) (i) Consider the following cell reaction at 298 K:
    2Ag+ + Cd → 2Ag + Cd2+
    The standard reduction potentials (E°) for Ag+/ Ag and Cd2+ /Cd are 0.80V and –0·40V respectively:
    (1) Write the cell representation.
    (2) What will be the emf of the cell if the concentration of Cd2+ is 0.1 M and that of Ag+ is 0·2 M?
    (3) Will the cell work spontaneously for the condition given in (2) above?

    (ii) What is a buffer solution? How is it prepared? Explain the buffer action of a basic buffer with a suitable example.

    (b) Explain the following:
    (i) When NaCl is added to AgNO3 solution, a white precipitate is formed.
    (ii) An aqueous solution of ammonium chloride is acidic in nature.

    (c) A 0·05 M NH4OH solution offers the resistance of 50 ohms to a conductivity cell at 298K. If the cell constant is 0·50 cm–1 and molar conductance of NH4OH at infinite dilution is 471.4 ohm–1 cm2 mol–1, calculate:
    (i) Specific conductance
    (ii) Molar conductance
    (iii) Degree of dissociation VIEW SOLUTION

  • Question 5
    (a) Write the IUPAC names of the following:
    (i) [Co(NH3)4SO4]NO3
    (ii) K[Pt(NH3)Cl3]

    (b) What type of isomerism is exhibited by the following pairs of compounds:
    (i) [PtCl2(NH3)4]Br2 and [PtBr2(NH3)4]Cl2
    (ii) [Cr(SCN)(H2O)5]2+ and [Cr(NCS)(H2O)5]2+

    (c) How does K2[PtCl4] get ionised when dissolved in water? Will it form precipitate when AgNO3 solution is added to it? Give a reason for your answer. VIEW SOLUTION

  • Question 6
    (a) Give balanced equations for the following reactions:
    (i) Silver nitrate is added to dilute solution of sodium thiosulphate.
    (ii) Potassium dichromate is treated with acidified ferrous sulphate solution.
    (iii) Phosphorous reacts with conc. sulphuric acid.

    (b) How will you obtain pure potassium permanganate (KMnO4) crystals from its ore, pyrolusite? Give the steps involved and the reactions. VIEW SOLUTION

  • Question 7
    (a) (i) Sulphur dioxide acts as an oxidizing agent as well as a reducing agent. Give one reaction each to show its oxidizing nature and its reducing nature.
    (ii) Explain why an aqueous solution of potassium hexacyanoferrate (II) does not give the test for ferrous ion.

    (b) What is meant by Lanthanide contraction? Write the general electronic configuration of inner transition elements. VIEW SOLUTION

  • Question 8
    (a) How can the following conversions be brought about:
    (i) Acetaldehyde to acetaldehyde phenyl hydrazone.
    (ii) Benzoic acid to aniline.
    (iii) Methyl chloride to acetone.
    (iv) Benzene to benzene diazonium chloride.

    (b) (i) Glycerol (propane 1, 2, 3 triol) is more viscous than ethylene glycol (ethane 1, 2, diol). Explain.
    (ii) How can urea be detected by Biuret test?

    (c) Identify the compounds A, B and C:

  • Question 9
    (a) Give balanced equations for the following name reactions:
    (i) Benzoin condensation
    (ii) Wurtz-Fittig reaction
    (iii) Carbylamine reaction

    (b) Give chemical test to distinguish:
    (i) Formaldehyde and acetaldehyde
    (ii) Dimethyl ether and ethyl alcohol.

    (c) (i) Write the structure of three ethers with molecular formula C4H10O.
    (ii) Starting with Grignard's reagent, how will you prepare propanoic acid? VIEW SOLUTION

  • Question 10
    (a) An organic compound A has the molecular formula C7H6O. When A is treated with NaOH followed by acid hydrolysis, it gives two products B and C. When B is oxidized, it gives A, when A and C are each treated separately with PCl5, they give two different products D and E.
    (i) Identify A, B, C, D and E.
    (ii) Give the chemical reaction when A is treated with NaOH and name the reaction.

    (b) Answer the following:
    (i) What do you observe when glucose solution is heated with Tollen's reagent?
    (ii) Name the monomers and the type of polymerisation in each of the following polymers:
    (1) Terylene
    (2) Polyvinyl chloride

    (c) Give balanced equations for the following reactions:
    (i) Ethylamine with nitrous acid.
    (ii) Diethyl ether with phosphorous pentachloride.
    (iii) Aniline with acetyl chloride. VIEW SOLUTION
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