Board Paper of Class 12-Science 2009 Chemistry (SET 1) - Solutions

A reaction is of second order with respect to a reactant. How will the rate of reaction be affected if the concentration of this reactant is

(i) Doubled,

(ii) Reduced to half?

Explain the role of

(i) Cryolite in the electrolytic reduction of alumina.

(ii) Carbon monoxide in the purification of nickel.

Draw the structures of the following molecules:

(i) XeF₄

(ii) BrF₃

Complete the following chemical reaction equations:

(i)

(ii)

Differentiate between molality and molarity of a solution. What is the effect of change in temperature of a solution on its molality and molarity?

Which ones in the following pairs of substances undergoes S_N2 substitution reaction faster and why?

(i)

(ii)

or

Complete the following reaction equations:

(i)

(ii)

Explain what is meant by

(i) A peptide linkage

(ii) A glycosidic linkage

Name two water soluble vitamins, their sources and the diseases caused due to their deficiency in diet.

Draw the structures of the monomers of the following polymers:

(i) Teflon

(ii) Polythene

OR

What is the repeating unit in the condensation polymer obtained by combining HO₂CCH₂CH₂CO₂H (succinic acid) and H₂NCH₂CH₂NH₂ (ethylene diamine)?

Iron has a body-centred cubic unit cell with a cell edge of 286.65 pm. The density of iron is 7.87 g cm⁻³. Use this information to calculate Avogadro’s number.

(At. Mass of Fe = 56 g mol⁻¹)

100 mg of a protein is dissolved in just enough water to make 10.0 mL of solution. If this solution has an osmotic pressure of 13.3 mm Hg at 25°C, what is the molar mass of the protein?

(R = 0.0821 L atm mol⁻¹ K⁻¹ and 760 mm Hg = 1 atm)

A first-order reaction has a rate constant of 0.0051 min⁻¹. If we begin with 0.10 M concentration of the reactant, what concentration of reactant will remain in the solution after 3 hours?

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

(i) An aerosol (ii) A hydrosol (iii) An emulsion

Account for the following:

(i) NH₃ is a stronger base than PH₃.

(ii) Sulphur has a greater tendency for catenation than oxygen.

(iii) Bond dissociation energy of F₂ is less than that of Cl₂.

OR

Explain the following situations:

(i) In the structure of HNO₃ molecule, the N − O bond (121 pm) is shorter than the N − OH bond (140 pm).

(ii) SF₄ is easily hydrolysed whereas SF₆ is not easily hydrolysed.

(iii) XeF₂ has a straight linear structure and not a bent angular structure.

For the complex [Fe(en)₂Cl₂] Cl, (en = ethylene diamine), identify

(i) The oxidation number of iron,

(ii) The hybrid orbitals and the shape of the complex,

(iii) The magnetic behaviour of the complex,

(iv) The number of geometrical isomers,

(v) Whether there is an optical isomer also, and

(vi) Name of the complex. (At. No. of Fe = 26)

Explain the mechanism of the following reactions:

(i) Addition of Grignard’s reagent to the carbonyl group of a compound forming an adduct followed by hydrolysis.

(ii) Acid catalysed dehydration of an alcohol forming an alkene.

(iii) Acid catalysed hydration of an alkene forming an alcohol.

Giving an example for each, describe the following reactions:

(i) Hofmann’s bromamide reaction

(ii) Gatterman reaction

(iii) A coupling reaction

Explain the following types of substances with one suitable example, for each case:

(i) Cationic detergents

(ii) Food preservatives

(iii) Analgesics

(a) Define molar conductivity of a substance and describe how for weak and strong electrolytes, molar conductivity changes with concentration of solute. How is such change explained?

(b) A voltaic cell is set up at 25°C with the following half cells:

Ag⁺ (0.001 M) | Ag and Cu²⁺ (0.10 M) | Cu

What would be the voltage of this cell?

()

OR

(a) State the relationship amongst the cell constant of a cell, the resistance of the solution in the cell and the conductivity of the solution. How is molar conductivity of a solute related to the conductivity of its solution?

(b) A voltaic cell is set up at 25°C with the following half-cells:

Al | Al³⁺ (0.001 M) and Ni | Ni²⁺ (0.50 M)

Calculate the cell voltage.

(a) Complete the following chemical reaction equations:

(i)

(ii)

(b) Explain the following observations about the transition/inner transition elements:

(i) There is in general an increase in density of element from titanium (Z = 22) to copper (Z = 29).

(ii) There occurs much more frequent metal−metal bonding in compounds of heavy transition elements (3^rd series).

(iii) The members of the actinoid series exhibit a larger number of oxidation states than the corresponding members of the lanthanoid series.

OR

(a) Complete the following chemical equations for reactions:

(i)

(ii)

(b) Give an explanation for each of the following observations:

(i) The gradual decrease in size (actinoid contractions) from element to element is greater among the actinoids than among the lanthanoids (lanthanoid contraction).

(ii) The greatest number of oxidation states are exhibited by the members in the middle of a transition series.

(iii) With the same d-orbital configuration (d⁴) Cr²⁺ ion is a reducing agent but Mn³⁺ ion is an oxidising agent.

(a) Illustrate the following name reactions by giving example:

(i) Cannizzaro’s reaction

(ii) Clemmensen reduction

(b) An organic compound A contains 69.77% carbon, 11.63% hydrogen and rest oxygen. The molecular mass of the compound is 86. It does not reduce Tollen’s reagent but forms an addition compound with sodium hydrogen sulphite and gives positive iodoform test. On vigorous oxidation it gives ethanoic and propanoic acids. Derive the possible structure of compound A.

OR

(a) How are the following obtained?

(i) Benzoic acid from ethyl benzene

(ii) Benzaldehyde from toluene

(b) Complete each synthesis by giving the missing material, reagent or products:

(i)

(ii)

(iii)