Board Paper of Class 12-Science 2011 Chemistry (SET 3) - Solutions

Calculate the packing efficiency of a metal crystal for a simple cubic lattice.

Explain how you can determine the atomic mass of an unknown metal if you know its mass density and the dimensions of unit cell of its crystal.

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

The thermal decomposition of HCO₂H is a first order reaction with a rate constant of 2.4 × 10⁻³ s⁻¹ at a certain temperature. Calculate how long will it take for three-fourths of initial quantity of HCO₂H to decompose.

(log 0.25 = − 0.6021)

What do you understand by the rate law and rate constant of a reaction?

Identify the order of a reaction if the units of its rate constant are:

(i) L⁻¹ mol s⁻¹

(ii) L mol⁻¹ s⁻¹

Describe the principle controlling each of the following processes:

(i) Preparation of cast iron form pig iron.

(ii) Preparation of pure alumina (Al₂O₃) from bauxite ore.

Explain giving reasons:

(i) Transition metals and their compounds generally exhibit a paramagnetic behaviour.

(ii) The chemistry of actinoids is not so smooth as that of lanthanoids.

Complete the following chemical equations:

(i)

(ii)

OR

State reasons for the following:

(i) Cu (I) ion is not stable in an aqueous solution.

(ii) Unlike Cr^3+, Mn^2+, Fe³⁺ and the subsequent other M²⁺ ions of the 3d series of elements, the 4d and the 5d series metals generally do not form stable cationic species.

Write the main structural difference between DNA and RNA. Of the four bases, name those which are common to both DNA and RNA.

Write such reactions and facts about glucose which cannot be explained by its open chain structure.

A solution prepared by dissolving 8.95 mg of a gene fragment in 35.0 mL of water has an osmotic pressure of 0.335 torr at 25°C.

Assuming that the gene fragment is a non-electrolyte, calculate its molar mass.

Classify colloids where the dispersion medium is water. State their characteristics and write an example of each of these classes.

OR

Explain what is observed when

(i) an electric current is passed through a sol

(ii) a beam of light is passed through a sol

(iii) an electrolyte (say NaCl) is added to ferric hydroxide sol

How would you account for the following:

(i) NF₃ is an exothermic compound but NCl₃ is not.

(ii) The acidic strength of compounds increases in the order:

PH₃ < H₂S < HCl

(iii) SF₆ is kinetically inert.

VIEW SOLUTION

Write the state of hybridization, the shape and the magnetic behaviour of the following complex entities:

(i) [Cr(NH₃)₄ Cl₂] Cl

(ii) [Co(en)₃] Cl₃

(iii) K₂ [Ni(CN)₄]

State reasons for the following:

(i) pK_b value for aniline is more than that for methylamine.

(ii) Ethylamine is soluble in water whereas aniline is not soluble in water.

(iii) Primary amines have higher boiling points than tertiary amines.

Rearrange the compounds of each of the following sets in order of reactivity towards S_N2 displacement:

(i) 2-Bromo-2-methylbutane, 1-Bromopentane, 2-Bromopentane

(ii) 1-Bromo-3-methylbutane, 2-Bromo-2-methylbutane, 3-Bromo-2-methylbutane

(iii) 1-Bromobutane, 1-Bromo-2, 2-dimethylpropane, 1-Bromo-2-methylbutane

How would you obtain the following:

(i) Benzoquinone from phenol

(ii) 2-methyl propan-2-ol from methyl-magnesium bromide

(iii) Propane-2-ol from propene

Write the names and structures of the monomers of the following polymers:

(i) Buna-S

(ii) Dacron

(iii) Neoprene

What are the following substances? Give one example of each.

(i) Food preservatives

(ii) Synthetic detergents

(iii) Antacids

(a) Draw the structures of the following molecules:

(i) (HPO₃)₃

(ii) BrF₃

(b) Complete the following chemical equations:

(i) HgCl₂ + PH₃ →

(ii) SO₃ + H₂SO₄ →

(iii) XeF₄ + H₂O →

OR

(a) What happens when

(i) chlorine gas is passed through a hot concentrated solution of NaOH?

(ii) sulphur dioxide gas is passed through an aqueous solution of a Fe (III) salt?

(b) Answer the following:

(i) What is the basicity of H₃PO₃ and why?

(ii) Why does fluorine not play the role of a central atom in inter-halogen compounds?

(iii) Why do noble gases have very low boiling points?

(a) What type of a battery is lead storage battery? Write the anode and cathode reactions and the overall cell reaction occurring in the operation of a lead storage battery.

(b) Calculate the potential for half-cell containing 0.10 M K₂Cr₂O₇ (aq), 0.20 M Cr³⁺ (aq) and 1.0 × 10⁻⁴ M H⁺ (aq)

The half-cell reaction is and the standard electrode potential is given as E⁰ = 1.33 V.

OR

(a) How many moles of mercury will be produced by electrolysing 1.0 M

Hg (NO₃)₂ solution with a current of 2.00 A for 3 hours?

[Hg(NO₃)₂ = 200.6 g mol⁻¹]

(b) A voltaic cell is set up at 25°C with the following half-cells Al³⁺ (0.001 M) and Ni²⁺ (0.50 M). Write an equation for the reaction that occurs when the cell generates an electric current and determine the cell potential.

(a) Illustrate the following name reactions:

(i) Cannizzaro’s reaction

(ii) Clemmensen reduction

(b) How would you obtain the following:

(i) But-2-enal from ethanal

(ii) Butanoic acid from butanol

(iii) Benzoic acid from ethylbenzene

OR

(a) Given chemical tests to distinguish between the following:

(i) Benzoic acid and ethyl benzoate

(ii) Benzaldehyde and acetophenone

(b) Complete each synthesis by giving missing reagents or products in the following:

(i)

(ii)

(iii)