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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
What is the formula of a compound in which the element Y forms ccp lattice and atoms of X occupy 2/3rd of octahedral voids ? VIEW SOLUTION

• Question 2
Write the IUPAC name of the given compound :
VIEW SOLUTION

• Question 3
Physisorption is reversible while chemisorption is irreversible. Why ? VIEW SOLUTION

• Question 4
Which would undergo SN2 reaction faster in the following pair and why ?
CH3 – CH2 ​– Br and CH3 ​– CH2 ​– I VIEW SOLUTION

• Question 5
Which allotrope of sulphur is thermally stable at room temperature ? VIEW SOLUTION

• Question 6
(a) Following reactions occur at cathode during the electrolysis of aqueous copper(II) chloride solution :

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

(b) State Kohlrausch law of independent migration of ions. Write its one application. VIEW SOLUTION

• Question 7
Why do transition elements show variable oxidation states? In 3d series (Sc to Zn), which element shows the maximum number of oxidation states and why? VIEW SOLUTION

• Question 8

(i) Write down the IUPAC name of the following complex :
[Cr(en)3]Cl3

(ii) Write the formula for the following complex :
Potassium trioxalatochromate(III)

VIEW SOLUTION

• Question 9

Name the reagents used in the following reactions:

VIEW SOLUTION

• Question 10
What is meant by negative deviation from Raoult's law? Give an example. What is the sign of ∆mixH for negative deviation?

OR

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

• Question 11
(a) Why are alkyl halides insoluble in water?
(b) Why is Butan-1-ol optically inactive but Butan-2-ol is optically active?
(c) Although chlorine is an electron withdrawing group, yet it is ortho-, para- directing in electrophilic aromatic substitution reactions. Why? VIEW SOLUTION

• Question 12
How do you convert the following :

(i) Benzoic acid to Benzaldehyde
(ii) Ethyne to Ethanal
(iii) Acetic acid to Methane

OR

Write the equations involved in the following reactions :

(i) Stephen reaction
(ii) Wolff-Kishner reduction
(iii) Etard reaction VIEW SOLUTION

• Question 13
Calculate the mass of NaCl (molar mass = 58.5 g mol−1) to be dissolved in 37.2 g of water to lower the freezing point by 2°C, assuming that NaCl undergoes complete dissociation. (Kf for water = 1.86 K kg mol−1) VIEW SOLUTION

• Question 14
Write the names and structures of the monomers of the following polymers:
(i) Terylene
(ii) Bakelite
(iii) Buna-S VIEW SOLUTION

• Question 15
(i) Which one of the following is a monosaccharide:
starch, maltose, fructose, cellulose
(ii) What is the difference between acidic amino acids and basic amino acids?
(iii) Write the name of the vitamin whose deficiency causes bleeding of gums. VIEW SOLUTION

• Question 16
(i) Draw the geometrical isomers of complex [Pt(en)2Cl2]2+.
(ii) On the basis of crystal field theory, write the electronic configuration for d4 ion, if ∆0 > P.
(iii) Write the hybridization type and magnetic behaviour of the complex [Ni(CN)4]2−. (Atomic number of Ni = 28) VIEW SOLUTION

• Question 17
(i) Indicate the principle behind the method used for the refining of Nickel.
(ii) What is the role of dilute NaCN in the extraction of gold?
(iii) What is 'copper matte'? VIEW SOLUTION

• Question 18
Calculate the emf of the following cell at 25°C :

Zn | Zn2+ (0.001 M) || H+ (0.01 M) | H2(g) (1 bar) | Pt(s)

VIEW SOLUTION

• Question 19
Predict the products of the following reactions :
(i)

(ii)

(iii) VIEW SOLUTION

• Question 20
An element X (molar mass = 60 g mol−1) has a density of 6.23 g cm−3. Identify the type of cubic unit cell, if the edge length of the unit cell is 4 ✕ 10−8 cm. VIEW SOLUTION

• Question 21
(a) How would you account the following :
(i) Highest fluoride of Mn is MnF4 whereas the highest oxide is Mn2O7.
(ii) Transition metals and their compounds show catalytic properties.

(b) Complete the following equation :
$3{\mathrm{MnO}}_{4}^{2-}+4{\mathrm{H}}^{+}\to$ VIEW SOLUTION

• Question 22

Give reasons for the following observations :

(i) A delta is formed at the meeting point of seawater and river water.

(ii) NH3 gas adsorbs more readily than N2 gas on the surface of the charcoal.

(iii) Powdered substances are more effective adsorbents.

VIEW SOLUTION

• Question 23

Seeing the growing cases of diabetes and depression among children, Mr. Chopra, the principal of one reputed school organized a seminar in which he invited parents and principals. They all resolved this issue by strictly banning the junk food in schools and by introducing 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. Chopra 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. Chopra ?

(iii) Why should antidepressant drugs not be taken without consulting a doctor ?

(iv) Give two examples of artificial sweeteners.

VIEW SOLUTION

• Question 24
(a) Illustrate the following reactions giving suitable example in each case :
(i) Ammonolysis
(ii) Coupling reaction
(iii) Acetylation of amines
(b) Describe Hinsberg method for the identification of primary, secondary and tertiary amines. Also write the chemical equations of the reactions involved.

OR

(a) Write the structures of main products when benzene diazonium chloride reacts with the following reagents :
(i) HBF4/∆
(ii) Cu/HBr

(b) Write the structures of A, B and C in the following reactions :
VIEW SOLUTION

• Question 25
(a) Define the following terms:
(i) Activation energy
(ii) Rate constant

(b) A first order reaction takes 10 minutes for 25% decomposition. Calculate t1/2 for the reaction.

(Given : log 2 = 0.3010, log 3 = 0.4771, log 4 = 0.6021)

OR

(a) For a chemical reaction R → P, the variation in the concentration, ln [R] vs. time (s) plot is given as

(i) Predict the order of the reaction.
(ii) What is the slope of the curve?
(iii) Write the unit of rate constant for this reaction.

(b) Show that the time required for 99% completion is double of the time required for the completion of 90% reaction. VIEW SOLUTION

• Question 26

(a) Account for the following :

(i) Bond angle in ${\mathrm{NH}}_{4}^{+}$ is higher than NH3.

(ii) H2S has lower boiling point than H2O.

(iii) Reducing character decreases from SO2 to TeO2.

(b) Draw the structures of the following :

(i) H​4P2O7 (Pyrophosphoric acid)

(ii) XeF2

OR

(a) Draw the structures of the following :

(i) XeF4

​(ii) H2S2O7

(b) Account for the following :

(i) Iron on reaction with HCl forms FeCl2 nd not FeCl3.

(ii) HClO4 is a stronger acid than HClO.

(iii) BiH3 is the strongest reducing agent amongst all the hydrides of group 15.

VIEW SOLUTION
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