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# Board Paper of Class 12-Science 2017 Chemistry (SET 3) - 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
Out of and , which is an example of a benzylic halide?       (1) VIEW SOLUTION
• Question 2
What is the effect of adding a catalyst on           (1)
(a) Activation energy (Ea), and
(b) Gibbs energy (ΔG) of a reaction? VIEW SOLUTION
• Question 3
Write the formula of the compound of iodine which is obtained when conc. HNO3 oxidises I2.            (1) VIEW SOLUTION
• Question 4
What type of colloid is formed when a gas is dispersed in a liquid? Give an example.    (1)   VIEW SOLUTION
• Question 5
Write the IUPAC name of the following compound:  (1)
VIEW SOLUTION
• Question 6
Draw the structures of the following:   (2)
(a) XeF4
(b) BrF5 VIEW SOLUTION
• Question 7
Write the name of the cell which is generally used in transistors. Write the reactions taking place at the anode and the cathode of this cell.    (2) VIEW SOLUTION
• Question 8
(a) Arrange the following compounds in the increasing order of their acid strength:   (2)

p-cresol, p-nitrophenol, phenol

(b) Write the mechanism (using curved arrow notation) of the following reaction:

OR

Write the structures of the products when Butan-2-ol reacts with the following:
(a) CrO3
(b) SOCl2 VIEW SOLUTION
• Question 9
Using IUPAC norms write the formulae for the following:  (2)

(a) Potassium trioxalatoaluminate(III)
(b) Dichloridobis(ethane-1,2-diamine)cobalt(III) VIEW SOLUTION
• Question 10
Calculate the number of unit cells in 8⋅1 g of aluminium if it crystallizes in a face-centred cubic (f.c.c.) structure. (Atomic mass of Al = 27 g mol−1)    (2) VIEW SOLUTION
• Question 11
(a) What type of isomerism is shown by the complex [Co(NH3)5(SCN)]2+?   (3)
(b) Why is [NiCl4]2− paramagnetic while [Ni(CN)4]2− is diamagnetic? (Atomic number of Ni = 28)
(c) Why are low spin tetrahedral complexes rarely observed? VIEW SOLUTION
• Question 12
Write one difference in each of the following:    (3)
(a) Multimolecular colloid and Associated colloid
(b) Coagulation and Peptization
(c) Homogeneous catalysis and Heterogeneous catalysis

OR

(a) Write the dispersed phase and dispersion medium of milk.
(b) Write one similarity between physisorption and chemisorption.
(c) Write the chemical method by which Fe(OH)3 sol is prepared from FeCl3. VIEW SOLUTION
• Question 13
(a) The cell in which the following reaction occurs:   (3)

has ${\mathrm{E}}_{\mathrm{cell}}^{\mathrm{o}}$ = 0·236 V at 298 K. Calculate the standard Gibbs energy of the cell reaction. (Given : 1 F = 96,500 C mol−1)

(b) How many electrons flow through a metllic wire if a current of 0·5 A is passed for 2 hours? (Given : 1 F = 96,500 C mol−1) VIEW SOLUTION
• Question 14
(a) Based on the nature of intermolecular forces, classify the following solids:   (3)

Sodium sulphate, Hydrogen

(b) What happens when CdCl2 is doped with AgCl?
(c) Why do ferrimagnetic substances show better magnetism than antiferromagnetic substances? VIEW SOLUTION
• Question 15
(a) Write the principle of electrolytic refining.   (3)
(b) Why does copper obtained in the extraction from copper pyrites have a blistered appearance?
(c) What is the role of depressants in the froth floatation process? VIEW SOLUTION
• Question 16
Write the structures of compounds A, B and C in the following reactions:   (3)

(a)

(b) VIEW SOLUTION
• Question 17
Give reasons for the following:   (3)

(a) Acetylation of aniline reduces its activation effect.
(b) CH3NH2 is more basis than C6H5NH2.
(c) Although − NH2 is o/p directing group, yet aniline on nitration gives a significant amount of m-nitroaniline. VIEW SOLUTION
• Question 18
Give reasons for the following:   (3)

(a) Red phosphorus is less reactive than white phosphorus.
(b) Electron gain enthalpies of halogens are largely negative.
(c) N2O5 is more acidic than N2O3. VIEW SOLUTION
• Question 19
Define the following:  (3)
(a) Cationic detergents
(b) Broad spectrum antibiotics
(c) Tranquilizers VIEW SOLUTION
• Question 20
Write the structures of the monomers used for getting the following polymers:   (3)
(a) Teflon
(b) Melamine-formaldehyde polymer
(c) Neoprene VIEW SOLUTION
• Question 21
The following compounds are given to you:    (3)
2-Bromopentane, 2-Bromo-2-methylbutane, 1-Bromopentane

(a) Write the compound which is most reactive towards SN2 reaction.
(b) Write the compounds which is optically active.
(c) Write the compounds which is most reactive towards β-elimination reaction. VIEW SOLUTION
• Question 22
A first order reaction takes 20 minutes for 25% decomposition. Calculate the time when 75% of the reaction will be completed.   (4)

(Given : log = 2 = 0·3010, log 3 = 0·4771, log 4 = 0·6021) VIEW SOLUTION
• Question 23
After watching a programme on TV about the presence of carcinogens (cancer causing agents) Potassium bromate and Potassium iodate in bread and other bakery products, Rupali a Class XII student decided to make others aware about the adverse effects of these carcinogens in foods. She consulted the school principal and requested him to instruct the canteen contractor to stop selling sandwiches, pizzas, burgers and other bakery products to the students. The principal took an immediate action and instructed the canteen contractor to replace the bakery products with some protein and vitamin rich food like fruits, salads, sprouts, ets. The decision was welcomed by the parents and the students.    (4)

After reading the above passage, answer the following questions:
(a) What are the values (at least two) displayed by Rupali?
(b) Which polysaccharide component of carbohydrates is commonly present in bread?
(c) Write the two type of secondary structures of proteins.
(d) Give two examples of water soluble vitamins. VIEW SOLUTION
• Question 24
(a) Write the product(s) in the following reactions:   (5)

(i)
(ii)
(iii)

(b) Give simple chemical tests to distinguish between the following pairs of compounds:
(i) Butanal and Butan-2-one
(ii) Benzoic acid and Phenol

OR

(a) Write the reaction involved in the following:
(i) Etard reaction
(ii) Stephen reduction

(b) How will you convert the following in not more than two steps:
(i) Benzoic acid to Benzaldehyde
(ii) Acetophenone to Benzoic acid
(iii) Ethanoic acid to 2-Hydroxyethanoic acid
VIEW SOLUTION
• Question 25
(a) Account for the following:     (5)
(i) Transition metals show variable oxidation states.
(ii) Zn, Cd and Hg are soft metals.
(iii) Eo value for the Mn3+/Mn2+ couple is highly positive (+ 1·57 V) as compared to Cr3+/Cr2+.

(b) Write one similarity and one difference between the chemistry of lanthanoid and actionoid elements.

OR

(a) Following are the transition metal ions of 3d series:

Ti4+, V2+, Mn3+, Cr3+

(Atomic numbers: Ti = 22, V = 23, Mn = 25, Cr = 24)

(i) Which ion is most stable in an aqueous solution and why?
(ii) Which ion is a strong oxidising agent and why?
(iii) Which ion is colourless and why?

(b) Complete the following equations:
(i)
(ii) VIEW SOLUTION
• Question 26
(a) A 10% solution (by mass) of sucrose in water has a freezing point of 269·15 K. Calculate the freezing point of 10% glucose in water if the freezing point of pure water is 273·15 K.     (5)

Given:
(Molar mass of sucrose = 342 g mol−1)
(Molar mass of glucose = 180 g mol−1)

(b) Define the following terms:
(i) Molality (m)
(ii) Abnormal molar mass

OR

(a) 30 g of urea (M = 60 g mol−1) is dissolved in 846 g of water. Calculate the vapour pressure of water for this solution if vapour pressure of pure water at 298 K is 23·8 mm Hg.
(b) Write two differences between ideal solutions and non-ideal solutions. VIEW SOLUTION
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