Chemistry: 2016:CBSE:[All India]:Set-II

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  • Q1

    Write the IUPAC name of the given compound:

     

    Marks:1
    Answer:

    The IUPAC name of the given compound is 2-phenylethanol.

     

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  • Q2

    Write the structure of an isomer of compound C4H9Br which is most reactive towards SN1 reaction.

    Marks:1
    Answer:

    The possible isomers from the formula C4H9Br are 1-Bromobutane, 2-Bromobutane, 1-Bromo2-methylpropane and 2-Bromo2-methylpropane. The isomer of C4H9Br, which is the most reactive towards SN1 reaction is the one that forms a tertiary carbocation upon the elimination of the leaving group. This isomer is 2-Bromo2-methylpropane and its structure is shown below:

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  • Q3

    What is the reason for the stability of colloidal sols?

    Marks:1
    Answer:

    There are two main reasons for the stability of colloidal sols:

    1. Electrostatic stabilisation: The stability of a colloidal solution is mainly due to the presence of equal and similar charges on the colloidal particles. The colloidal particles repel one another and are thus are unable to combine together to form larger particles. This keeps them dispersed in the medium and the colloidal solution remains stable. This is why sol particles do not settle down even on standing for a long time. 
     

    2. Brownian movement: The constant rapid zig-zag motion of the particles plays an important role in imparting stability to the sol. This is because Brownian movement opposes the gravitational forces acting on colloidal particles and prevents them from settling down.

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  • Q4

    Give an example each of a molecular solid and an ionic solid.

    Marks:1
    Answer:

    The examples of molecular solids include ice (H2O) and solid ammonia.

    The examples of ionic solids include sodium chloride (NaCl) and magnesium oxide (MgO).

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  • Q5

    Pb(NO3)2 on heating gives a brown gas which undergoes dimerization on cooling. Identify the gas.

    Marks:1
    Answer:

    Pb(NO3)2 on heating gives brown coloured nitrogen dioxide gas which on cooling dimerizes to dinitrogen tetroxide (N2O4).

     

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  • Q6

    For a reaction:

    (i) Write the order and molecularity of this reaction.

    (ii) Write the unit of k.

    Marks:2
    Answer:

    (i) Since, rate = k, the given reaction is a zero-order reaction. On the basis of stoichiometry, the molecularity of the reaction is 2.

    (ii) The unit of rate constant (k) is mole L–1 sec–1.

     

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  • Q7

    Write the chemical equations involved in the following reactions:

    (i) Hoffmann-bromamide degradation reaction

    (ii) Carbylamine reaction

    Marks:2
    Answer:

    i. Hofmann bromamide degradation reaction:
    It is the method of preparation of primary amines in which acid amide is treated with an aqueous or ethanolic solution of sodium hydroxide and bromine. Primary amine so formed has one carbon atom less than the original amide. The reaction is used in step down conversion.

    ii. Carbylamine reaction

    The reaction is used as a test for primary amines. Aliphatic and aromatic primary amines on heating with chloroform and alcoholic potassium hydroxide form isocyanides that are foul smelling substances.

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  • Q8

    i. Gas (A) is more soluble in water than gas (B) at the same temperature. Which one of the two gases will have the higher value of KH (Henry’s constant) and why?

    ii. In non-ideal solution, what type of deviation shows the formation of maximum boiling azeotropes?

     

    Marks:2
    Answer:

    i.  According to Henry’s law, the solubility of a gas is inversely related to the Henry’s constant (KH) for that gas. Since, gas (B), is less soluble, it will have a higher KH value.

    ii. A maximum boiling azeotrope shows negative deviation from the Raoult’s law.

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  • Q9

    When a coordination compound CoCl3.6NH3 is mixed with AgNO3, 3 moles of AgCl are precipitated per mole of the compound. Write

    (i) Structural formula of the complex

    (ii) IUPAC name of the complex

    Marks:2
    Answer:

    (i)   Formation of 3 moles of AgCl indicates that all the 3 Cl ions in the coordination compound CoCl3.6NH3 must be present outside the coordination sphere and they will satisfy the primary valency. Therefore, the structural formula of the complex will be [Co(NH3)6]Cl3.

    (ii) The IUPAC name of the complex is Hexaamminecobalt (III) chloride.

     

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  • Q10

    Write the structures of the following:
    i. BrF3         
    ii. XeF4     

    Marks:2
    Answer:

    i. Structure of BrF3: Bent T-shaped

    ii. Structure of XeF4: Square planar

     

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