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# Board Paper of Class 12-Science 2019 Chemistry Delhi(Set 1) - Solutions

General Instructions:

(i) All questions are compulsory

(ii) Section A : Q. no. 1 to 5 are very short-answer questions and carry 1 mark each.

(iii) Section B : Q. no. 6 to 12 are short-answer questions and carry 2 marks each.

(iv) Section C : Q. no. 13 to 24 are also short-answer questions and carry 3 marks each.

(v) Section D : Q. no. 25 to 27 are long-answer questions and carry 5 marks each.

(vi) There is no overall choice. However, an internal choice has been provided in two questions of one mark, two questions of two marks, four questions of three marks and all the three questions of five marks weightage. You have to attempt only one of the choices in such questions.

(vii) Use log tables if necessary. Use of calculators is not allowed.

• Question 1
Out of NaC​l and AgCl, which one shows Frenkel; defect and why? VIEW SOLUTION
• Question 2
Arrange the following in increasing order of boiling points:

(CH3)3N, C2H5OH, C2H5NH2

VIEW SOLUTION
• Question 3

Why are medicines more effective in colloidal state?

OR

What is difference between an emulsion and a gel?

VIEW SOLUTION
• Question 4
Define ambident nucleophile with an example. VIEW SOLUTION
• Question 5
What is the basic structural difference between glucose and fructose?

OR

Write the products obtained after hydrolysis of lactose. VIEW SOLUTION
• Question 6

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

VIEW SOLUTION
• Question 7
State Raoult's law for a solution containing volatile components. Write two characteristics of the solution which obeys Raoult's law at all concentrations. VIEW SOLUTION
• Question 8
For a reaction

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
• Question 9
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
• Question 10
Write IUPAC name of the complex [Pt(en)2Cl2]. Draw structures of geometrical isomers for this complex.
OR
Using IUPAC norms write the formulae for the following:
(i) Hexaamminecobalt(III) sulphate
(ii) Potassium trioxalatochromate(III) VIEW SOLUTION
• Question 11
Out of [CoF6]3− and [Co(en)3]3+, which one complex is
(i) paramagnetic
(ii) more stable
(iii) inner orbital complex and
(iv) high spin complex
(Atomic no. of Co = 27) VIEW SOLUTION
• Question 12
Write structures of compounds A and B in each of the following reactions:
VIEW SOLUTION
• Question 13
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
• Question 14
(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?

VIEW SOLUTION
• Question 15
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
• Question 16
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
• Question 17

(a) Name the method of refining which is

(i) used to obtain semiconductor of high purity,

(ii) used to obtain low boiling metal.

(b) Write chemical reactions taking place in the extraction of copper from Cu2S.

VIEW SOLUTION
• Question 18
Give reasons for the following:

(i) Transition elements and their compounds act as catalysts.

(ii) E° value for (Mn2+|Mn) is negative whereas for (Cu2+|Cu) is positive.

(iii) Actinoids show irregularities in their electronic configuration.

VIEW SOLUTION
• Question 19
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?

VIEW SOLUTION
• Question 20
(i) Why type of drug is used in sleeping pills?
(ii) What type of detergent are used in toothpastes?
(iii) Why the use of alitame as artificial sweetener is not recommended?

OR

Define the following terms with a suitable example in each:
(ii) Disinfectants
(iii) Cationic detergents VIEW SOLUTION
• Question 21

(i) Out of (CH3)3C – Br and (CH3)3 C – I, which one is more reactive towards SN1 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?

VIEW SOLUTION
• Question 22
An aromatic compound 'A' on heating with Br2 and KOH forms a compound 'B' of molecular formula C6H7N which on reacting with CHCl3 and alcoholic KOH produces a foul smelling compound 'C'. Write the structures and IUPAC names of compounds A, B and C. VIEW SOLUTION
• Question 23

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.

VIEW SOLUTION
• Question 24
Differentiate between the following:
(i) Amylose and Amylopectin
(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
• Question 25
cell for the given redox reaction is 2.71 V
Mg(s) + Cu2+ (0.01 M) → Mg2+(0.001 M) + Cu(s)
Calculate Ecell 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
OR

(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 (c1/2), following curves are obtained for two electrolytes A and B:

(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
• Question 26

(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.

VIEW SOLUTION
• Question 27
(A) Give reasons for the following:
(i) Sulphur in vapour state shows paramagnetic behaviour.
(ii) N-N bond is weaker than P-P bond.
(iii) Ozone is thermodynamically less stable than oxygen.

(b) Write the name of gas released when Cu is added to
(i) dilute HNO3 and
(ii) conc. HNO3

OR

(a) (i) Write the disproportionation reaction of H3PO3.
(ii) Draw the structure of XeF4.

(b) Account for the following:
(i) Although Fluorine has less negative electron gain enthalpy yet F2 is strong oxidizing agent.
(ii) Acidic character decreases from N2O3 to Bi2O3 in group 15.

(c) Write a chemical reaction to test sulphur dioxide gas. Write chemical equation involved. VIEW SOLUTION
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