12th Chemistry Paper Solutions Set 2 : CBSE All India 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 :

Zn2+ salts are white while Cu2+ salts are coloured. Why ?


Answer :

Element/Ion Electronic Configuration
Zn 3d10 4s2
Zn2+ 3d10
Cu 3d10 4s1
Cu2+ 3d9

The colours of salts of transition metals are due to the d-d transition that depend on the presence of incompletely filled d-orbitals. Zn2+ has completely filled d-orbitals (3d10), while Cu2+ has incompletely filled d-orbitals (3d9); therefore, d-d transition is possible in Cu2+, which imparts colour to copper(II) salts.

Q2 :

Which would undergo SN1 reaction faster in the following pair:


Answer :

A tertiary alkyl halide tends to undergo the SN1 mechanism because it can form a tertiary carbocation, which is stabilised by the three alkyl groups attached to it. As alkyl groups are electron donating, they allow the positive charge in the carbocation to be delocalised by the induction effect. Hence, out of the given pairs, (CH3)3C-Br would undergo SN1 reaction faster than CH3-CH2-Br.

Q3 :

How much charge is required for the reduction of 1 mol of Zn2+ to Zn?


Answer :

Zn2+ + 2e- → Zn
Number of electrons involved = 2
Charge required for the reduction of Zn2+ = 2F
We know
1F = 96,487 C
Thus,
2F = 2 × 96487 = 1,92,974 C

Q4 :

Write the dispersed phase and dispersion medium of butter.


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Q5 :

Write the IUPAC name of the given compound:


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Q6 :

Write the structures of the following molecules:
(i) H2SO3
(ii) XeOF4


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Q7 :

Write down the IUPAC name of the complex [Pt(en)2Cl2]2+. What type of isomerism is shown by this complex?
 

OR

Using IUPAC norms write the formulate for the following coordination compounds :
(i) Hexaamminecobalt (III) chloride
(ii) Potassium tetrachloridonickelate (II)


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Q8 :

Define rate of reaction? Write two factors that affect the rate of reaction.


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Q9 :

Arrange the following in increasing order of their basic strength :

(i) C6H5 – NH2, C6H5 – CH2 – NH2, C6H5 – NH – CH3

 


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Q10 :

Why does a solution containing non-volatile solute have higher boiling point than the pure solvent ? Why is elevation of boiling point a colligative property ?


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Q11 :

(i) What is the principle behind the zone refining of metals?
(ii) What is the role of silica in the extraction of copper?
(iii) How is 'cast iron' different from 'pig iron'?


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Q12 :

Give reasons for the following :
(i) N2 is less reactive at room temperature.
(ii) H2Te is the strongest reducing agent amongst all the hydrides of Group 16 elements.
(iii) Helium is used in diving apparatus as a diluent for oxygen.


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Q13 :

(a) Write the hybridization and shape of the following complexes :

(i) [CoF6]3–

(ii) [Ni(CN)4]2–

(Atomic number : Co = 27, Ni = 28)


(b) Out of NH3 and CO, which ligand forms a more stable complex with a transition metal and why?


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Q14 :

How do you convert the following:
(i) C6H5CONH2 to C6H5NH2
(ii) Aniline to phenol
(iii) Ethanenitrile to ethanamine


OR

Write the chemical equations involved when aniline is treated with the following reagents:
(i) Br2 water
(ii) CHCI3 + KOH
(iii) HCI


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Q15 :

Write the names and structures of the monomers of the following polymers:
(i) Buna-S
(ii) Glyptal
(iii) Polyvinyl chloride


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Q16 :

(i) Write the product obtained when D-glucose reacts with H2N − OH.
(ii) Amino acids show amphoteric behaviour. Why?
(iii) Why cannot vitamin C be stored in our body?


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Q17 :

Calculate the freezing point of the solution when 31 g of ethylene glycol (C2H6O2) is dissolved in 500 g of water. (Kf for water = 1.86 K kg mol–1)


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Q18 :

Define the following terms :

(i) Primitive unit cells

(ii) Schottky defect

(iii) Ferromagnetism


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Q19 :

Write the structure of the major product in each of the following reactions :
     


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Q20 :

Give reasons for the following :
(i) Phenol is more acidic than ethanol.
(ii) Boiling point of ethanol is higher in comparison to methoxymethane.
(iii) (CH3)3C − O − CH3 on reaction with HI gives CH3OH and (CH3)3C − I as the main products and not (CH3)3C − OH and CH3I.


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Q21 :

The rate constant of a first order reaction increases from 2 × 10−2 to 4 × 10−2 when the temperature changes from 300 K to 310 K. Calculate the energy of activation (Ea).

(log 2 = 0.301, log 3 = 0.4771, log 4 = 0.6021)


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Q22 :

Define the following terms :
(i) Brownian movement
(ii) Peptization
(iii) Multimolecular colloids


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Q23 :

Seeing the growing cases of diabetes and depression among young children, Mr. Lugani, the principal of on reputed school organized a seminar in which he invited parents and principals. They all resolved this issue by strictly banning junk food in schools and introducing healthy snacks and drinks like soup, lassi, milk, etc. in school canteens. They also decided to make compulsory half an hour of daily physical activities for the students in the morning assembly. After six months, Mr. Lugani conducted the health survey is most of the schools and discovered a tremendous improvement in the health of the students.
After reading the above passage, answer the following questions :
(i) What are the values (at least two) displayed by Mr. Lugani?
(ii) As a student, how can you spread awareness about this issue?
(iii) What are antidepressant drugs? Give an example.
(iv) Name the sweetening agent used in the preparation of sweets for a diabetic patient.


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Q24 :

Calculate e.m.f. and ∆G for the following cell:
Mg (s) âˆ£âˆ£Mg2+ (0.001 M)∣∣∣∣ Cu2+


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Q25 :

(a) Account for the following :

(i) Zr and Hf have almost similar atomic radii.

(ii) Transition metals show variable oxidation states.

(iii) Cu+ ion is unstable in aqueous solution.

(b) Complete the following equations :

(i) 2 MnO2 + 4 KOH + O2 â†’

(ii) 2 Na2CrO4 + 2 H + â†’​

OR

​(a)

E0(M2+/M) Cr Mn Fe Co Ni


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Q26 :

(a) A compound 'A' of molecular formula C2H3OCl undergoes a series of reactions as shown below. Write the structures of A, B, C and D in the following reactions :

(C2H3OCl) A -→--------  H2


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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.