12th Chemistry Paper Solutions Set 2 : CBSE Abroad Previous Year 2015

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.
Q1 :

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 ?


Answer :

Number of octahedral voids formed = Number of atoms of element Y
Number of atoms of element Y in the ccp unit cell = 4
∴ Number of octahedral voids formed = 4

Now,
Number of octahedral voids occupied by atoms of X = 23x4=83
Ratio of the numbers of atoms of X and Y = 83 : 4

Hence, the formula of the compound is X2Y3.

Q2 :

Write the IUPAC name of the given compound :


Answer :

Q3 :

Physisorption is reversible while chemisorption is irreversible. Why ?


Answer :

Physisorption takes place with the help of non-covalent bonding between an adsorbate and an adsorbent; it makes the process reversible. Chemisorption, on the other hand, takes place with the help of covalent bonding; it makes the process irreversible.

Q4 :

Which would undergo SN2 reaction faster in the following pair and why ?
CH3 – CH2 ​– Br and CH3 ​– CH2 ​– I


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Q5 :

Which allotrope of sulphur is thermally stable at room temperature ?


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Q6 :

(a) Following reactions occur at cathode during the electrolysis of aqueous copper(II) chloride solution :
Cu2+(aq) + 2e--→---              


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Q7 :

Why do transition elements show variable oxidation states ? In 3d series (Sc to Zn), which elements shows the maximum number of oxidation state and why ?


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Q8 :

(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)


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Q9 :

Name the reagents used in the following reactions:


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Q10 :

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.


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Q11 :

(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?


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Q12 :

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


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Q13 :

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)


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Q14 :

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


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Q15 :

(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.


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Q16 :

(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)


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Q17 :

(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' ?


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Q18 :

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)

E0(Zn2+/Zn)=-0.76 V,      E0


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Q19 :

Predict the products of the following reactions :
(i) CH3-CH=CH2-→----------       ii


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Q20 :

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.


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Q21 :

(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 :
3MnO2-4+4H+→


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Q22 :

Give reasons for the following observations :

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

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

(iii) Powdered substances are more effective  adsorbents.


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Q23 :

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.
After reading the above passage, answer the following questions :

(i) What are the values (at least two) displayed by Mr. Chopra ?

(ii) As a student, how can you spread awareness about this issue ?

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

(iv) Give two examples of artificial sweeteners.


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Q24 :

(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 (C6 H5 N+2CI-) reacts with the following reagents :
(i) HBF4/∆
(ii) Cu/HBr
(b) Write the structures of A, B and C in the following reactions :


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Q25 :

(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.


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Q26 :

(a) Account for the following :

(i) Bond angle in 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.


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12th Chemistry Paper Solutions Set 3 : CBSE Delhi Previous Year 2013 will be available online in PDF book soon. The solutions are absolutely Free. Soon you will be able to download the solutions.