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# Board Paper of Class 12-Science 2015 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
Which would undergo SN2 reaction faster in the following pair and why ?

VIEW SOLUTION

• Question 2
Out of BaCl2 and KCl, which one is more effective in causing coagulation of a negatively charged colloidal Sol? Give reason. VIEW SOLUTION

• Question 3
What is the formula of a compound in which the element Y forms ccp lattice and atoms of X occupy 1/3rd of tetrahedral voids? VIEW SOLUTION

• Question 5
Write the IUPAC name of the given compound :

VIEW SOLUTION

• Question 6

Name the reagents used in the following reactions:

VIEW SOLUTION

• Question 7
What is meant by positive deviations from Raoult's law? Give an example. What is the sign of ∆mixH for positive deviation?

OR

Define azeotropes. What type of azeotrope is formed by positive deviation from Raoult's law ? Give an example. VIEW SOLUTION

• Question 8
(a) Following reactions occur at cathode during the electrolysis of aqueous silver chloride solution :

On the basis of their standard reduction electrode potential (E°) values, which reaction is feasible at the cathode and why ?

(b) Define limiting molar conductivity. Why conductivity of an electrolyte solution decreases with the decrease in concentration ? VIEW SOLUTION

• Question 9
What are the transition elements? Write two characteristics of the transition elements. VIEW SOLUTION

• Question 10
(i) Write down the IUPAC name of the following complex:
[Cr(NH3)2Cl2(en)]Cl (en = ethylenediamine)

(ii) Write the formula for the following complex:
Pentaamminenitrito-o-Cobalt (III). VIEW SOLUTION

• Question 11
(i) Draw the geometrical isomers of complex [Pt(NH3)2Cl2].
(ii) On the basis of crystal field theory, write the electronic configuration for d4 ion if ∆0 < P.
(iii) Write the hybridization and magnetic behaviour of the complex [Ni(CO)4].
(At.no. of Ni = 28) VIEW SOLUTION

• Question 12
Calculate emf of the following cell at 25 °C :
VIEW SOLUTION

• Question 13
Give reasons for the following observations :
(i) Leather gets hardened after tanning.
(ii) Lyophilic sol is more stable than lyophobic sol.
(iii) It is necessary to remove CO when ammonia is prepared by Haber's process. VIEW SOLUTION

• Question 14
Write the names and structures of the monomers of the following polymers

(i) Nylon-6, 6
(ii) PHBV
(iii) Neoprene VIEW SOLUTION

• Question 15

Predict the products of the following reactions :

VIEW SOLUTION

• Question 16
How do you convert the following :
(i) Phenol to anisole
(ii) Propan-2-ol to 2-methylpropan-2-ol
(iii) Aniline to phenol

OR

(a) Write the mechanism of the following reaction :

(b) Write the equation involved in the acetylation of Salicylic acid. VIEW SOLUTION

• Question 17
(i) Which one of the following is a disaccharide : Starch, Maltose, Fructose, Glucose ?
(ii) What is the difference between fibrous protein and globular protein ?
(iii) Write the name of vitamin whose deficiency causes bone deformities in children. VIEW SOLUTION

• Question 18
Give reasons :
(a) n-Butyl bromide has higher boiling point than t-butyl bromide.
(b) Racemic mixture is optically inactive.
(c) The presence of nitro group (−NO2) at o/p positions increases the reactivity of haloarenes towards nucleophilic substitution reactions. VIEW SOLUTION

• Question 19
3.9 g of benzoic acid dissolved in 49 g of benzene shows a depression in freezing point of 1.62 K. Calculate the van't Hoff factor and predict the nature of solute (associated or dissociated).

(Given : Molar mass of benzoic acid = 122 g mol−1, Kf for benzene = 4.9 K kg mol−1) VIEW SOLUTION

• Question 20
(i) Indicate the principle behind the method used for the refining of zinc.
(ii) What is the role of silica in the extraction of copper?
(iii) Which form of the iron is the purest form of commercial iron? VIEW SOLUTION

• Question 21
An element with molar mass 27 g mol−1 forms a cubic unit cell with edge length 4.05 ✕ 10−8 cm. If its density is 2.7 g cm−3, what is the nature of the cubic unit cell? VIEW SOLUTION

• Question 22
(a) How would you account for the following :
(i) Actinoid contraction is greater than lanthanoid contraction.
(ii) Transition metals form coloured compounds

(b) Complete the following equation :
$2{\mathrm{MnO}}_{4}^{-}+6{\mathrm{H}}^{+}+5{\mathrm{NO}}_{2}^{-}\to$ VIEW SOLUTION

• Question 23
Mr. Roy, the principal of one reputed school organized a seminar in which he invited parents and principals to discuss the serious issue of diabetes and depression in students. They all resolved this issue by strictly banning the junk food in schools and to introduce healthy snacks and drinks like soup, lassi, milk etc. in school canteens. They also decided to make compulsory half an hour physical activities for the students in the morning assembly daily. After six months, Mr. Roy conducted the health survey in most of the schools and discovered a tremendous improvement in the health of students.

(i) What are the values (at least two) displayed by Mr. Roy ?
(iii) What are tranquillizers ? Give an example.
(iv) Why is use of aspartame limited to cold foods and drinks ? VIEW SOLUTION

• Question 24

An aromatic compound 'A' of molecular formula C7H7ON undergoes a series of reactions as shown below. Write the structures of A, B, C, D and E in the following reactions :

OR

(a) Write the structures of main products when aniline reacts with the following reagents :

(i) Br2 water

(ii) HCl

(iii) (CH3CO)2O/pyridine

(b) Arrange the following in the increasing order of their boiling point :

C2H5NH2, C2H5OH, (CH3)3N

​(c) Give a simple chemical test to distinguish between the following pair of compounds :

(CH3)2NH and (CH3)3N
VIEW SOLUTION

• Question 25

For the hydrolysis of methyl acetate in aqueous solution, the following results were obtained :

 t/s 0 30 60 [CH3COOCH3] / mol L–1 0.6 0.3 0.15

(i) Show that it follows pseudo first order reaction, as the concentration of water remains constant.

(ii) Calculate the average rate of reaction between the time interval 30 to 60 seconds.

(Given log 2 = 0.3010, log 4 = 0.6021)

Or

(a) For a reaction A + B → P, the rate is given by

Rate = k[A] [B]2

(i) How is the rate of reaction affected if the concentration of B is doubled ?

(ii) What is the overall order of reaction if A is present in large excess ?

(b) A first order  reaction takes 30 minutes for 50% completion. Calculate the time required for 90% completion of this reaction.

(log 2 = 0.3010)

VIEW SOLUTION

• Question 26

(a) Account for the following :

(i) Acidic character increases from HF to HI.

(ii) There is large difference between the melting and boiling points of oxygen and sulphur.

(iii) Nitrogen does not form pentahalide.

(b) Draw the structures of the following :

(i) ClF3

(ii) XeF4

OR

(i) Which allotrope of phosphorus is more reactive and why?

(ii) How the supersonic jet aeroplanes are responsible for the depletion of ozone layers?

(iii) F2 has lower bond dissociation enthalpy than Cl2. Why?

(iv) Which noble gas is used in filling balloons for meteorological observations?

(v) Complete the equation :​

VIEW SOLUTION
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