Board Paper of Class 12-Science 2016 Chemistry (SET 2) - Solutions

General Instructions :
(i) All questions are compulsory.
(ii) Q. no. 1 to 5 are very short answer questions and carry 1 mark each.
(iii) Q. no. 6 to 10 are short answer questions and carry 2 marks each.
(iv) Q. no. 11 to 22 are also short answer questions and carry 3 marks each.
(v) Q. no. 23 is a value based question and carry 4 marks.
(vi) Q. no. 24 to 26 are long answer questions and carry 5 marks each.
(vii) Use log tables if necessary, use of calculators is not allowed.

Question 1
Write the IUPAC name of the given compound:

VIEW SOLUTION

Question 2
Write the main reason for the stability of colloidal sols. VIEW SOLUTION

Question 3
Out of and , which is more reactive towards S_N1 reaction and why? VIEW SOLUTION

Question 4
On adding NaOH to ammonium sulphate, a colourless gas with pungent odour is evolved, which forms a blue-coloured complex with Cu²⁺ ion. Identify the gas. VIEW SOLUTION

Question 5
What type of magnetism is shown by a substance if magnetic moments of domains are arranged in same direction? VIEW SOLUTION

Question 6
For a reaction : $2 {NH}_{3} (g) \to_{}^{Pt} N_{2} (g) + 3 H_{2} (g) Rate = k$
(i) Write the order and molecularity of this reaction.

(ii) Write the unit of k. VIEW SOLUTION

Question 7
Write the mechanism of the following reaction:

$2 {CH}_{3} {CH}_{2} OH \to_{413 K}^{Conc . H_{2} {SO}_{4}} {CH}_{3} - {CH}_{2} - O - {CH}_{2} - {CH}_{3}$ VIEW SOLUTION

Question 8
From the given cells:
Lead storage cell, Mercury cell, Fuel cell and Dry cell
Answer the following:
(i) Which cell is used in hearing aids?
(ii) Which cell was used in Apollo Space Programme?
(iii) Which cell is used in automobiles and inverters?
(iv) Which cell does not have long life? VIEW SOLUTION

Question 9
When chromite ore FeCr₂O₄ is fused with NaOH in presence of air, a yellow-coloured compound (A) is obtained, which on acidification with dilute sulphuric acid gives a compound (B). Compound (B) on reaction with KCl forms an orange coloured crystalline compound (C).

(i) Write the formulae of the compounds (A), (B) and C.
(ii) Write one use of compound (C).

OR

Complete the following chemical equations:
(i) $8 {MnO}_{4}^{-} + 3 S_{2} O_{3}^{2 -} + H_{2} O \underset{}{\to}$
(ii) ${Cr}_{2} O_{7}^{2 -} + 3 {Sn}^{2 +} + 14 H^{+} \underset{}{\to}$ VIEW SOLUTION

Question 10
When a co-ordination compound CrCl₃.6H₂O is mixed with AgNO₃, 2 moles of AgCl are precipitated per mole of the compound. Write
(i) Structural formula of the complex.
(ii) IUPAC name of the complex. VIEW SOLUTION

Question 11

(i) Differentiate between adsorption and absorption.

(ii) Out of MgCl₂ and AlCl₃, which one is more effective in causing coagulation of negatively charged sol and why?

(iii) Out of sulphur sol and proteins, which one form multimolecular colloids?
VIEW SOLUTION

Question 12
(i) Name the method of refining of metals such as Germanium.

(ii) In the extraction of Al, impure Al₂O₃ is dissolved in conc. NaOH to form sodium aluminate and leaving impurities behind. What is the name of this process?

(iii) What is the role of coke in the extraction of iron from its oxides? VIEW SOLUTION

Question 13
Calculate e.m.f of the following cell at 298 K:

2Cr(s) + 3Fe²⁺ (0.1M) → 2Cr³⁺ (0.01M) + 3 Fe(s)

Given: E°(Cr³⁺ | Cr) = – 0.74 VE° (Fe²⁺| Fe) = – 0.44 V VIEW SOLUTION

Question 14
Given reasons:

(i) C–Cl bond length in chlorobenzene is shorter than C–Cl bond length in CH₃–Cl.

(ii) The dipole moment of chlorobenzene is lower than that of cyclohexyl chloride.

(iii) S_N1 reactions are accompanied by racemization in optically active alkyl halides. VIEW SOLUTION

Question 15
An element crystallizes in a f.c.c. lattice with cell edge of 250 pm. Calculate the density if 300 g of this element contain 2 × 10²⁴ atoms. VIEW SOLUTION

Question 16
The rate constant for the first-order decomposition of H₂O₂ is given by the following equation:

$\log k = 14.2 - \frac{1.0 \times 10^{4}}{T} K$

Calculate E_a for this reaction and rate constant k if its half-life period be 200 minutes.

(Given: R = 8.314 JK^–1 mol^–1) VIEW SOLUTION

Question 17
(i) What is the role of t-butyl peroxide in the polymerization of ethene?
(ii) Identify the monomers in the following polymer:

(iii) Arrange the following polymers in the increasing order of their intermolecular forces:

Polystyrene, Terylene, Buna-S

OR

Write the mechanism of free radical polymerization of ethene. VIEW SOLUTION

Question 18
(i) Write the name of two monosaccharides obtained on hydrolysis of lactose sugar.

(ii) Why Vitamin C cannot be stored in our body ?

(iii) What is the difference between a nucleoside and nucleotide ? VIEW SOLUTION

Question 19
(a) For the complex [Fe(CN)₆]^3–, write the hybridization type, magnetic character and spin nature of the complex. (At. number : Fe = 26).

(b) Draw one of the geometrical isomers of the complex [Pt(en)₂Cl₂]²⁺ which is optically active. VIEW SOLUTION

Question 20
Give reasons:

(i) Mn shows the highest oxidation state of +7 with oxygen but with fluorine, it shows the highest oxidation state of +4.

(ii) Transition metals show variable oxidation states.

(iii) Actinoids show irregularities in their electronic configurations. VIEW SOLUTION

Question 21
Write the main product(s) in each of the following reactions:

(i)

(ii)

(iii)
VIEW SOLUTION

Question 22
Write the structures of A, B and C in the following:

(i)

(ii)
VIEW SOLUTION

Question 24

(a) Calculate the freezing point of solution when 1.9 g of MgCl₂ (M = 95 g mol⁻¹) was dissolved in 50 g of water, assuming MgCl₂ undergoes complete ionization.
(K_f for water = 1.86 K kg mol⁻¹)

(b) (i) Out of 1 M glucose and 2 M glucose, which one has a higher boiling point and why?

(ii) What happens when the external pressure applied becomes more than the osmotic pressure of solution?

OR

(a) When 2.56 g of sulphur was dissolved in 100 g of CS₂, the freezing point lowered by 0.383 K. Calculate the formula of sulphur (S_x).

(K_f for CS₂ = 3.83 K kg mol⁻¹, Atomic mass of sulphur = 32 g mol⁻¹]

(b) Blood cells are isotonic with 0.9% sodium chloride solution. What happens if we place blood cells in a solution containing

(i) 1.2% sodium chloride solution?
(ii) 0.4% sodium chloride solution?
VIEW SOLUTION

Question 25
(a) Account for the following :
(i) Ozone is thermodynamically unstable.
(ii) Solid PCl₅ is ionic in nature.
(iii) Fluorine forms only one oxoacid HOF.

(b) Draw the structure of
(i) BrF₅
(ii) XeF₄

OR

(i) Compare the oxidizing action of F₂and Cl₂ by considering parameters such as bond dissociation enthalpy, electron gain enthalpy and hydration enthalpy.

(ii) Write the conditions to maximize the yield of H₂SO₄ by contact process.

(iii) Arrange the following in the increasing order of property mentioned :
(a) H₃PO₃, H₃PO₄, H₃PO₂(Reducing character)
(b) NH₃, PH₃, AsH₃, SbH₃, BiH₃ (Base strength)
VIEW SOLUTION

Question 26
Write the structures of A, B, C, D and E in the following reactions:

OR

(a) Write the chemical equation for the reaction involved in Cannizzaro reaction.
(b) Draw the structure of the semicarbazone of ethanal.
(c) Why pKa of F-CH₂-COOH is lower than that of Cl−CH₂−COOH?
(d) Write the product in the following reaction:

(e) How can you distinguish between propanal and propanone? VIEW SOLUTION

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