Plustwo Chemistry – Some Questions for Practice

  1. An element ‘A’ exists as a yellow solid in standard state. It forms a volatile hydride ‘B’ which is a foul smelling gas
    and is extensively used in qualitative analysis of salts. When treated with oxygen, ‘B’ forms an oxide ‘C’ which is
    a colourless, pungent smelling gas. This gas when passed through acidified KMnO4 solution, decolourises it. ‘C’
    gets oxidized to another oxide ‘D’ in the presence of a heterogeneous catalyst. Identify A,B,C,D, and also give the
    chemical equation of reaction of ‘C’ with acidified KMnO4 solution and for conversion of ‘C’ to ‘D’.
  2. (a) An organic compound ‘A’ with molecular formula C5H8O2 is reduced to n-pentane on treatment with Zn-Hg/
    HCI. ‘A’ forms a dioxime with hydroxylamine and gives a positive lodoform test and Tollen’s test. Identify the
    compound A and deduce its structure.
    (b) Write the chemical equations for the following conversions:
    (not more than 2 steps)
    (i) Ethyl benzene to benzene
    (ii) Acetaldehyde to butane – 1, 3 – diol
    (iii) Acetone to propene 5
  3. Give reasons for the following:
    (a) Transition metals have high enthalpies of atomization.
    (b) Among the lanthanoids, Ce(III) is easily oxidised to Ce(IV).
    (c) redox couple has less positive electrode potential than couple.
    (d) Copper (I) has d10 configuration,while copper (II) has d9 configuration, still copper (II) is more stable in
    aqueous solution than copper (I).
    (e) The second and third transition series elements have almost similar atomic radii.
  4. (a) A blackish brown coloured solid ‘A’ when fused with alkali metal hydroxides in presence of air, produces a
    dark green coloured compound ‘B’, which on electrolytic oxidation in alkaline medium gives a dark purple coloured
    compound C. Identify A, B and C and write the reactions involved.
    (b) What happens when an acidic solution of the green compound (B) is allowed to stand for some time? Give the
    equation involved. What is this type of reaction called?
  5. (a) Calculate the standard free energy change for the following reaction at 250C
    Predict whether the reaction will be spontaneous or not at 250C. Which of the above two half cells will act as an
    oxidizing agent and which one will be a reducing agent?
    (b) The conductivity of 0.001M acetic acid is 4 x 10-5S / cm. Calculate the dissociation constant of acetic acid, if
    for acetic acid is 390. 5S cm2/mol.
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