Chemistry: 2015:CBSE:[Delhi]:Set -III

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  • Q1

    Out of BaCl2 and KCl, which one is more effective in causing coagulation of a negatively charged colloidal Sol? Give reason.

    Marks:1
    Answer:

    According to the Hardy–Schulze rule, the greater the charge of a coagulating ion, the greater is its power to cause precipitation of the oppositely charged ion. Between Ba2+ (from BaCl2) and K+ (from KCl), Ba2+ has greater charge. Therefore, it will be more effective in causing the coagulation of a negatively charged colloidal sol.

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  • Q2

    What is the formula of a compound in which the element Y forms ccp lattice and atoms of X occupy 1/3rd of tetrahedral voids?

    Marks:1
    Answer:

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  • Q3

    What is the basicity of H3PO4 ?

    Marks:1
    Answer:

    Basicity of oxoacid of Phosphorus = Total no. of P–OH bonds
    Hence, its basicity is 3.

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  • Q4

    Write the IUPAC name of the given compound:

    Marks:1
    Answer:

    2,5-Dinitrophenol

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  • Q5

    Which would undergo SN2 reaction faster in the following pair and why?

    Marks:1
    Answer:

    For SN2 reactions the rate of reaction is faster for primary alkyl halides as compared to tertiary alkyl halides because of less steric hindrance experienced by the approaching nucleophile. Hence, out of the given pair (CH3−CH2−Br) would undergo SN2 reaction faster.

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  • Q6

    What is meant by positive deviations from Raoult's law? Give an example. What is the sign of ∆mixH for positive deviation?

    Marks:2
    Answer:

    The non ideal solutions having vapour pressure higher than the solution exhibit positive deviation from Raoult’s law. In case of positive deviation from Raoult’s law, the intermolecular attractive forces between the solute-solvent molecules are weaker than those between the solute-solute and solvent-solvent molecules.

    Heat is absorbed during the formation of such solutions and ΔmixH has a positive sign. Volume of the solution formed is more, i.e. DmixV > 0

    A mixture of ethanol and acetone is an example of a solution that shows a positive deviation from Raoult’s law.

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  • Q7

    Define azeotropes. What type of azeotrope is formed by positive deviation from Raoult's law ? Give an example.

    Marks:2
    Answer:

    Azeotropes are the binary mixtures of solutions that have the same composition in liquid and vapour phases and boil at constant temperature. It is not possible to separate their components by fractional distillation.

    A minimum-boiling azeotrope is formed by solutions showing a positive deviation from Raoult’s law at a specific composition. Example: An ethanol–water mixture containing approximately 95% ethanol by volume.

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  • Q8

    a) Following reactions occur at cathode during the electrolysis of aqueous silver chloride solution:

    On the basis of their standard reduction electrode potential (E°) values, which reaction is feasible at the cathode and why?

    b) Define limiting molar conductivity. Why conductivity of an electrolyte solution decreases with the decrease in concentration?

    Marks:2
    Answer:

    a) Given:

    The relationship between the standard free energy change and EMF of a cell reaction is given by
    ΔG°=−nFE°

    Thus, the more positive the standard reduction potential of a reaction, the more negative is the standard free energy change associated with the process and consequently, the higher is the feasibility of the reaction.

    Since, E° (Ag+/Ag) has a greater positive value than E° (H+/H), the reaction which is feasible at the cathode is given by

    b) Limiting molar conductivity is the molar conductivity of the solution when the concentration of the electrolyte approaches zero (at infinite dilution).

    The conductivity of an electrolyte solution is the conductance of ions present in a unit volume of the solution. The number of ions (required for conduction) decreases when the solution is diluted or the concentration is decreased. As a result, the conductivity of an electrolyte solution decreases with the decrease in concentration.

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  • Q9

    What are the transition elements? Write two characteristics of the transition elements.

    Marks:2
    Answer:

    The elements having incompletely filled d-orbitals either in their ground state or in any of their oxidation states are known as transition elements.
    Characteristics of transition elements are as follows:
    1. They show variable oxidation states.
    2. They generally form coloured compounds.

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  • Q10

    Marks:2
    Answer:

    [Cr(NH3)2Cl2(en)]Cl
    IUPAC Name: Diamminedichlorido(ethane-1,2-diamine)chromium(III) chloride

    (ii) Pentaamminenitrito-O-Cobalt (III)
    Formula: [Co(NH3)5(ONO)]2+

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