Board Paper of Class 12-Science 2019 Chemistry Delhi(Set 2) - Solutions

Write structures of compounds A and B in each of the following reactions:
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For a reaction
$2{\mathrm{H}}_2{\mathrm{O}}_2\underset{\mathrm{alkaline} \mathrm{medium}}{\overset{{\mathrm{I}}^{-}}{\to }}2{\mathrm{H}}_2\mathrm{O}+{\mathrm{O}}_2$
the proposed mechanism is as given below:
(1) H₂O₂ + I⁻ → H₂O + IO⁻ (slow) 
(2) H₂O₂ + IO⁻ → H₂O + I⁻ + O₂ (fast)

(i) Write rate law for the reaction.
(ii) Write the overall order of reaction.
(iii) Out of steps (1) and (2), which one is rate determining step? VIEW SOLUTION

Write two differences between an ideal solution and a non-ideal solution.

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When MnO₂ is fused with KOH in the presence of KNO₃ as an oxidizing agent, it gives a dark  green compound (A). Compound (A) disproportionates in acidic solution to give purple compound (B). An alkaline solution of compound (B) oxidises KI to compound (C) whereas an acidified solution of compound (B) oxidises KI to (D). Identify (A), (B), (C), and (D). VIEW SOLUTION

Write IUPAC name of the complex [Cr(NH₃)₄Cl₂ ]⁺. Draw structures of geometrical isomers for this complex.
                                                    OR
Using IUPAC norms write the formulae for the following:
(i) Pentaamminenitrito-O-cobalt(III) chloride
( ii) Potassium tetracyanidonickelate(II) VIEW SOLUTION

Out of [CoF₆]³⁻ and [Co(C₂O₄)₃]³⁻, which one complex is
(i) diamagnetic
(ii) more stable
(iii) outer orbital complex and
(iv) low spin complex?
(Atomic no. of Co = 27) VIEW SOLUTION

Write balanced chemical equations for the following processes:

(i) XeF₂ undergoes hydrolysis.

(ii) MnO₂ is heated with conc. HCl.

OR

Arrange the following in order of property indicated for each set:

(i) H₂O, H₂S, H₂Se, H₂Te - increasing acidic character

(ii) HF, HCl, HBr, HI - decreasing bond enthalpy

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An element crystallizes in fcc lattice with a cell edge of 300 pm. The density of the element is 10.8 g cm⁻³. Calculate the number of atoms in 108 g of the element. VIEW SOLUTION

A 4% solution(w/w) of sucrose (M = 342 g mol⁻¹) in water has a freezing point of 271.15 K. Calculate the freezing point of 5% glucose (M = 180 g mol⁻¹) in water.
(Given: Freezing point of pure water = 273.15 K) VIEW SOLUTION

The Decomposition of NH₃ on the platinum surface is zero order reaction. If rate constant (k) is 4  × 10⁻³ Ms⁻¹, how long it will take to reduce the initial concentration of NH₃ from 0.1 M to 0.064 M. VIEW SOLUTION

(i)  What is the role of activated charcoal in gas mask?

(ii) A colloidal sol is prepared by the given method in figure. What is the charge on hydrated ferric oxide colloidal particles formed in the test tube? How is the sol represented?



(iii) How does chemisorption vary with temperature?

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(i) Write the role of 'CO' in the purification of nickel.
(ii) What is the role of silica in the extraction of copper?
(iii) What type of metals are generally extracted by electrolytic method? VIEW SOLUTION

Give reasons for the following:

(i) Transition metals form alloys.
(ii) Mn₂O₃ is basic whereas Mn₂O₇ is acidic.
(iii) Eu²⁺ is a strong reducing agent.
  VIEW SOLUTION

Write the structures of monomers used for getting the following polymers:

(i) Nylon-6,6

(ii) Glyptal

(iii) Buna-S

OR

(i) Is  a homopolymer or copolymer? Give reason.

(ii) Write the monomers of the following polymer:

(iii) What is the role of Sulphur in the vulcanization of rubber?

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(i) Why bithional is added in soap?
(ii) Why magnesium hydroxide is a better antacid than sodium bicarbonate?
iii) Why soaps are biodegradable whereas detergents are non-biodegradable? Define the following terms with a suitable example in each:
(i) Antibiotics
(ii) Artificial sweeteners
(iii) Analgesics
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Write the structures of main products when benzene diazonium chloride reacts with the following reagents:
(i)  CuCN
(ii) CH₃CH₂OH
(iii) KI VIEW SOLUTION

(i) Out of (CH₃)₃C – Br and (CH₃)₃ C – I, which one is more reactive towards S_N1 and why?

(ii) Write the product formed when p-nitrochlorobenzene is heated with aqueous NaOH at 443 K followed by acidification.

(iii) Why dextro and laevo – rotatory isomers of Butan-2-ol are difficult to separate by fractional distillation?

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Differentiate between the following:
(i) Amylose and Amylopectin
(ii) Peptide linkage and Glycosidic linkage
(iii) Fibrous proteins and Globular proteins

OR

Write chemical reactions to show that open structure of D-glucose contains the following:
(i) Straight chain
(ii) Five alcohol groups
(iii) Aldehyde as carbonyl group VIEW SOLUTION

Complete the following reactions:

OR

Write chemical equations for the following reactions:
(i) Propanone is treated with dilute Ba(OH)₂.
(ii) Acetophenone is treated with Zn(Hg)/Conc. HCl
(iii) Benzoyl chloride is hydrogenated in presence of Pd/BaSO₄.

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(A) Give reasons for the following:
(b) Write the name of gas released when Cu is added to  
(a) (i) Write the disproportionation reaction of H₃PO₃.
(b) Account for the following:
(c) Write a chemical reaction to test sulphur dioxide gas. Write chemical equation involved. VIEW SOLUTION

E°_cell for the given redox reaction is 2.71 V
Mg_(s) + Cu²⁺ _{(0.01 M)} → Mg²⁺(0.001 M) + Cu_(s)
Calculate E_cell for the reaction. Write the direction of flow of current when an external opposite potential applied is
(i) less than 2.71 V and
(ii) greater than 2.71 V
(a) A steady current of 2 amperes was passed through two electrolytic cells X and Y connected in series containing electrolytes FeSO₄ and ZnSO₄ until 2.8 g of Fe deposited at the cathode of cell X. How long did the current flow? Calculate the mass of Zn deposited at the cathode of cell Y.
(Molar mass : Fe = 56 g mol^–1 Zn = 65.3 g mol^–1, 1F = 96500 C mol^–1)

(b) In the plot of molar conductivity (∧_m) vs square root of concentration (c^1/2), following curves are obtained for two electrolytes A and B:


Answer the following:
(i) Predict the nature of electrolytes A and B.
(ii) What happens on extrapolation of ∧_m to concentration approaching zero for electrolytes A and B? VIEW SOLUTION

(a) How do you convert the following:
      (i) Phenol to Anisole
      (ii) Ethanol to Propan-2-ol

(b) Write mechanism of the following reaction:
${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}\underset{443\mathrm{K}}{\overset{{\mathrm{H}}_2{\mathrm{SO}}_4}{\to }}{\mathrm{CH}}_2={\mathrm{CH}}_2+{\mathrm{H}}_2\mathrm{O}$

(c) Why phenol undergoes electrophilic substitution more easily than benzene?

OR

(a) Account for the following:
      (i) o-nitrophenol is more steam volatile than p-nitrophenol.
      (ii) t-butyl chloride on heating with sodium methoxide gives 2-methylpropene instead of t-butylmethylether.

(b) Write the reaction involved in the following:
      (i) Reimer-Tiemann reaction
      (ii) Friedal-Crafts Alkylation of Phenol

(c) Give simple chemical test to distinguish between Ethanol and Phenol.

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