Board Paper of Class 12-Science 2010 Chemistry (SET 3) - Solutions

Draw the structures of white phosphorus and red phosphorus. Which one of these two types of phosphorus is more reactive and why?

The rate constant for a reaction of zero order in A is 0.0030 mol L⁻¹ s⁻¹. How long will it take for the initial concentration of A to fall from 0.10 M to 0.075 M?

A reaction is of first order in reactant A and of second order in reactant Β. How is the rate of this reaction affected when (i) the concentration of B alone is increased to three times (ii) the concentrations of A as well as B are doubled?

Non-ideal solutions exhibit either positive or negative deviations from Raoult’s law. What are these deviations and why are they caused? Explain with one example for each type.

Explain the following observations:

(i) Transition elements generally form coloured compounds.

(ii) Zinc is not regarded as a transition element.

How are the following conversions carried out?

(i) Benzyl chloride to benzyl alcohol,

(ii) Methyl magnesium bromide to 2-methylpropan-2-ol

Illustrate the following reactions giving a chemical equation for each:

(i) Kolbe’s reaction,

(ii) Williamson synthesis.

Explain the following terms:

(i) Invert sugar

(ii) Polypeptides

OR

Name the products of hydrolysis of sucrose. Why is sucrose not a reducing sugar?

Name the following coordination compounds according to IUPAC system of nomenclature:

(i) [Co(NH₃)₄ (H₂O)Cl] Cl₂

(ii) [CrCl₂ (en)₂] Cl, (en = ethane − 1, 2 − diamine)

State clearly what are known as nucleosides and nucleotides.

The density of copper metal is 8.95 g cm⁻³. If the radius of copper atom is 127.8 pm, is the copper unit cell a simple cubic, a body-centred cubic or a face centred cubic structure? (Given: At. Mass of Cu = 63.54 g mol⁻¹ and N_A = 6.02 × 10²³ mol⁻¹)

How are the following colloids different from each other in respect of their dispersion medium and dispersed phase? Give one example of each.

(i) Aerosol

(ii) Emulsion

(iii) Hydrosol

A solution prepared by dissolving 1.25 g of oil of winter green (methyl salicylate) in 99.0 g of benzene has a boiling point of 80.31 °C. Determine the molar mass of this compound. (B.P. of pure benzene = 80.10 °C and K_b for benzene = 2.53 °C kg mol⁻¹)

Describe how the following changes are brought about:

(i) Pig iron into steel

(ii) Zinc oxide into metallic zinc

(iii) Impure titanium into pure titanium.

OR

Describe the role of

(i) NaCN in the extraction of gold from gold ore.

(ii) SiO₂ in the extraction of copper from copper matte.

(iii) Iodine in the refining of zirconium.

Write chemical equations for the involved reactions.

(i) State oneuseeach of DDT and iodoform.

(ii) Which compound in the following couples will react faster in S_N2 displacement and why?

(a) 1-Bromopentane or 2-bromopentane

(b) 1-bromo-2-methylbutane or 2-bromo-2-methylbutane.

How would you account for the following?

(i) The atomic radii of the metals of the third (5d) series of transition elements are virtually the same as those of the corresponding members of the second (4d) series.

(ii) The E^° Value for the Mn³⁺/Mn²⁺ couple is much more positive than that for Cr³⁺/Cr²⁺ couple or Fe³⁺/Fe²⁺ couple.

(iii) The highest oxidation state of a metal is exhibited in its oxide or fluoride.

In the following cases rearrange the compounds as directed:

(i) In an increasing order of basic strength:

C₆H₅NH₂,C₆H₅ N (CH₃)₂, (C₂H₅)₂ NH and CH₃NH₂

(ii) In a decreasing order of basic strength:

Aniline, p-nitroaniline and p-toluidine

(iii) In an increasing order of pK_b values:

C₂H₅NH₂, C₆H₅ NHCH₃, (C₂H₅)₂ NH and C₆H₅NH₂

Differentiate between thermoplastic and thermosetting polymers. Give one example of each.

Explain the following terms with one suitable example in each case.

(i) Cationic detergents

(ii) Enzymes

(iii) Antifertility drugs

(a) Explain the mechanism of a nuclophilic attack on the carbonyl group of an aldehyde or a ketone.

(b) An organic compound (A) (molecular formula C₈H₁₆O₂) was hydrolysed with dilute sulphuric acid to give a carboxylic acid (B) and an alcohol (C). Oxidation of (C) with chromic acid also produced (B). On dehydration (C) gives but-1-ene. Write the equations for the reactions involved.

OR

(a) Give chemical tests to distinguish between the following pairs of compounds:

(i) Ethanal and Propanal

(ii) Phenol and Benzoic acid

(b) How will you bring about the following conversions?

(i) Benzoic acid to benzaldehyde

(ii) Ethanal to but-2-enal

(iii) Propanone to propene

Give complete reaction in each case.

(a) State Kohlrausch law of independent migration of ions. Write an expression for the molar conductivity of acetic acid at infinite dilution according to Kohlrausch law.

(b) Calcualte for acetic acid.

Given that (HCl) = 426 S cm² mol⁻¹

(NaCl) = 126 S cm² mol⁻¹

(CH₃COONa) = 91 S cm² mol⁻¹

OR

(a) Write the anode and cathode reactions and the overall reaction occurring in a lead storage battery.

(b) A copper-silver cell is set up. The copper ion concentration is 0.10 M. The concentration of silver ion is not known. The cell potential when measured was 0.422 V. Determine the concentration of silver ions in the cell. (Given)

(a) Complete the following chemical equations:

(b) How would you account for the following?

(i) The value of electron gain enthalpy with negative sign for sulphur is higher than that for oxygen.

(ii) NF₃ is an exothermic compound but NCl₃ is endothermic compound.

(iii) ClF₃ molecule has a T-shaped structure and not a trigonal planar one.

OR

(a) Complete the following chemical reaction equations:

(i) P₄ + SO₂Cl₂ →

(ii) XeF₄ + H₂O →

(b) Explain the following observations giving appropriate reasons:

(i) The stability of + 5 oxidation state decreases down the group in group 15 of the periodic table.

(ii) Solid phosphorus pentachloride behaves as an ionic compound.

(iii) Halogens are strong oxidizing agents.