Board Paper of Class 12-Science 2012 Chemistry (SET 3) - Solutions

A 1.00 molal aqueous solution of trichloroacetic acid (CCl₃COOH) is heated to its boiling point. The solution has the boiling point of 100.18°C. Determine the van’t Hoff factor for trichloroacetic acid. (K_b for water = 0.512 kg mol⁻¹)

OR

Define the following terms:

(i) Mole fraction

(ii) Isotonic solutions

(iii) Van’t Hoff factor

(iv) Ideal solution

Name the two groups into which phenomenon of catalysis can be divided. Give an example of each group with the chemical equation involved.

What do you understand by the ‘order of a reaction’? Identify the reaction order from each of the following units of reaction rate constant:

(i) L⁻¹ mol s⁻¹

(ii) L mol⁻¹ s⁻¹

Explain the following terms giving one example for each:

(i) Miscelles

(ii) Aerosol

Explain the following giving an appropriate reason in each case.

(i) O₂ and F₂ both stabilize higher oxidation states of metals but O₂ exceeds F₂ in doing so.

(ii) Structures of Xenon fluorides cannot be explained by Valence Bond approach.

Describe the principle involved in each of the following processes.

(i) Mond process for refining of Nickel.

(ii) Column chromatography for purification of rare elements.

What is meant by (i) peptide linkage (ii) biocatalysts?

Complete the following chemical equations:

(i)

(ii)

Draw the structure of the monomer for each of the following polymers:

(i) Nylon 6

(ii) Polypropene

Write any two reactions of glucose which cannot be explained by the open chain structure of glucose molecule.

Tungsten crystallizes in body centred cubic unit cell. If the edge of the unit cell is 316.5 pm, what is the radius of tungsten atom?

OR

Iron has a body centred cubic unit cell with a cell dimension of 286.65 pm. The density of iron is 7.874 g cm⁻³. Use this information to calculate Avogadro’s number (At. Mass of Fe = 55.845 u)

15.0 g of an unknown molecular material was dissolved in 450 g of water. The resulting solution was found to freeze at −0.34°C. What is the molar mass of this material? (K_f for water

= 1.86 K kg mol⁻¹)³

For the reaction

2NO_(g) + Cl_2(g) → 2 NOCl_(g)

The following data were collected. All the measurements were taken at 263 K:

(a) Write the expression for rate law.

(b) Calculate the value of rate constant and specify its units.

(c) What is the initial rate of disappearance of Cl₂ in exp. 4?

Explain the following observations giving as appropriate reason for each.

(i) The enthalpies of atomization of transition elements are quite high.

(ii) There occurs much more frequent metal-metal bonding in compounds of heavy transition metals (i.e 3^rd series).

(iii) Mn²⁺ is much more resistant than Fe²⁺ towards oxidation.

Write the name, the structure and the magnetic behaviour of each one of the following complexes:

(i) [Pt (NH₃)Cl(NO₂)]

(ii) [Co(NH₃)₄ Cl₂]Cl

(iii) Ni(CO)₄

(At.nos. Co = 27, Ni = 28, Pt = 78)

Write chemical equation for the following conversions:

(i) Nitrobenzene to benzoic acid.

(ii) Benzyl chloride to 2-phenylethanamine.

(iii) Aniline to benzyl alcohol.

Although chlorine is an electron withdrawing group, yet it is ortho-, para-directing in electrophilic aromatic substitution reactions. Explain why it is so?

Draw the structure and name the product formed if the following alcohols are oxidized. Assume that an excess of oxidizing agent is used.

(i) CH₃CH₂CH₂CH₂OH

(ii) 2-butenol

(iii) 2-methyl-1-proponal

Explain the following terms giving one example of each type:

(i) Antacids,

(ii) Disinfectants,

(iii) Enzymes.

(a) What type of a battery is the lead storage battery? Write the anode and the cathode reactions and the overall reaction occurring in a lead storage battery when current is drawn from it.

(b) In the button cell, widely used in watches, the following reaction takes place

Determine E° and ΔG° for the reaction

OR

(a) Define molar conductivity of a solution and explain how molar conductivity changes with change in concentration of solution for a weak and a strong electrolyte.

(b) The resistance of a conductivity cell containing 0.001 M KCl solution at 298 K is 1500Ω. What is the cell constant if the conductivity of 0.001 M KCl solution at 298 K is 0.146 × 10⁻³ S cm⁻¹?

(a) Illustrate the following name reaction giving suitable example in each case:

(i) Clemmensen reduction

(ii) Hell-Volhard-Zelinsky reaction

(b) How are the following conversions carried out?

(i) Ethylcyanide to ethanoic acid

(ii) Butan-1-ol to butanoic acid

(iii) Benzoic acid to m-bromobenzoic acid

OR

(a) Illustrate the following reactions giving a suitable example for each.

(i) Cross aldol condensation

(ii) Decarboxylation

(b) Give simple tests to distinguish between the following pairs of compounds

(i) Pentan-2-one and Pentan-3-one

(ii) Benzaldehyde and Acetophenone

(iii) Phenol and Benzoic acid

(a) Draw the molecular structures of following compounds:

(i) XeF₆

(ii) H₂S₂O₈

(b) Explain the following observations:

(i) The molecules NH₃ and NF₃ have dipole moments which are of opposite direction.

(ii) All the bonds in PCl₅ molecule are not equivalent.

(iii) Sulphur in vapour state exhibits paramagnetism.

OR

(a) Complete the following chemical equations:

(i) XeF₄ + SbF₅ →

(ii) Cl₂ + F₂ (excess) →

(b) Explain each of the following:

(i) Nitrogen is much less reactive than phosphorus.

(ii) The stability of +5 oxidation state decreases down group 15.

(iii) The bond angles (O − N − O) are not of the same value in