CBSE Sample Paper Class XII Chemistry

Chemistry (Code-A)

Sample Question Paper for Class XII

SAMPLE QUESTION PAPER Chemistry (Theory) - Class XII (Code-A) Time : 3 Hours

Max. Marks : 70

General Instructions : (i) All questions are compulsory. (ii) The question paper consists of four sections A, B, C and D. Section A contains 8 questions of 1 mark each. Section B is of 10 questions of 2 marks each. Section C has 9 questions of 3 marks each, whereas Section D is of 3 questions of 5 marks each. (iii) There is no overall choice. However, an internal choice has been provided in one question of 2 marks, one question of 3 marks and all three questions of 5 marks weightage. A student has to attempt only one of the alternatives in such questions. (iv) Wherever necessary, the diagrams drawn should be neat and properly labelled..

SECTION-A Very Short Answer Type Questions : 1.

[8 × 1 = 8]

Give IUPAC name of the compound:

— —

Br

— —

F

[1]

C2H5

C2H5

CH3 — C — CH2 — C — CH3

2.

Consider the reaction R  P. The change in the concentration of R with time is shown in the following plot. [1]

[R]t Time (i) Predict the order of the reaction. (ii) Write the expression for half life of this reaction. 3.

Predict the shape of BrF3 on the basis of VSEPR theory.

[1]

4.

What are the dispersed phase and dispersion medium in milk?

[1]

5.

A compound contains two type of atoms A and B. It crystalises in a cubic lattice with atom A at the corners of the cube and atom B at the face centres. What is the simplest formula of the compound? [1]

6.

An ionic compound AB is 50% dissociated in aqueous solution. Determine the value of Van’t Holf factor for this compound. [1]

7.

An ore sample of galena (PbS) is contaminated with zinc blende (ZnS). Name one chemical which can be used to concentrate selectively by froth floatation method. [1]

8.

Write balanced equation for the complete hydrolysis of XeF4. (1)

[1]

Sample Question Paper for Class XII

Chemistry (Code-A)

SECTION-B Short Answer Type Questions :

[10 × 2 = 20]

9.

Write the structure of 4-Methylpent-3-en-2-one. Will it respond positive to iodoform test? If so, Why?

[2]

10.

Define osmotic pressure. How does it change with

[2]

(a) Temperature (b) Atmospheric pressure 11.

Write the equations of the reactions involved in the extraction of copper from its sulphide ore (Cu2S).

[2]

12.

Name the two components of starch. How do they differ from each other structurally?

[2]

13.

Give the equations of the reactions involved when glucose is treated with

[2]

(a) HI (b) (CH3CO)2O 14.

Describe the mechanism of the formation of ethene from ethanol in the presence of concentrated sulphuric acid. [2]

15.

Give one example each of

[2]

(a) Hofmann bromamide reaction (b) Gabriel phthalimide reaction 16.

Distinguish chemically between

[2]

(a) Butan-1-ol and 2-Methyl propan-2-ol (b) Phenol and benzyl alcohol 17.

Account for the following:

[2]

(a) Aniline does not undergo Friedel Crafts alkylation (b) Aniline undergoes bromination even in the absence of halogen carrier OR (a) Unlike alkylation, acylation of amines stops after first step (b) Tertiary amines do not undergo acylation 18.

Explain the type of deviation shown by a mixture of acetone and chloroform.

[2]

SECTION-C Short Answer Type Questions : 19.

[9 × 3 = 27]

An element X with atomic mass 60 g/mole has a density 6.23 g/cm3. If the edge length of unit cell is 400 pm, identify the type of cubic unit cell. Calculate the radius of an atom of this element. (NA = 6 × 1023 mole–1) [3]

20.

Write the names of the monomers of these polymers and classify them as addition or condensation polymers. [3] (a) Terylene (b) Teflon (c) Natural rubber (2)

Chemistry (Code-A)

21.

Sample Question Paper for Class XII

(a) Name the isomerism exhibited by the following pair of coordination compounds:

[3]

[Co(NH 3)5Br]SO4 & [Co(NH3) 5SO 4]Br. Give one chemical test to distinguish between these two compounds. (b) Using valence bond theory compare the structures of [FeF6]4– and [Fe(CN)6]4– (Atomic number of Fe = 26) 22.

Give three differences each between

[3]

(a) Physisorption and chemisorption (b) Lyophilic sol and lyophobic sol 23.

Account for the following :

[3]

(a) ICl is more reactive than l2 (b) NO2 dimerises to form N2O4 (c) H3PO3 is a reducing agent but not H3PO4 24.

Give the structures of the following compounds :

[3]

(a) XeOF4 (b) PF5 (c) Peroxo disulphuric acid OR Give the products and balance the following equations: (a) Ca3P2 + H2O  (b) XeF6 + NaF  (c) Cu + H2SO4 (conc.)  25.

Activation energy of a reaction at 300 K is 55 kJ/mole. When the same reaction is carried out in the presence of a catalyst, activation energy is lowered to 45 kJ/mole at 300 K. Determine the extent to which the rate of the reaction is increased. [3]

26.

Account for the following:

[3]

(a) Haloalkanes react with KCN to give alkyl cyanide as a major product and not alkyl isocyanide. (b) In chloro benzene, Cl is electron withdrawing group but it undergoes electrophilic substitution at ortho and para position. (c) Allyl chloride is more reactive towards nucleophilic substitution than n-propyl chloride. 27.

Why are vitamin A and C essential to us? Also tell their chemical names.

[3]

SECTION-D Long Answer Type Questions :

[3 × 5 = 15]

28. (a) Carry out the following conversions:

[3]

(i) Ethanal to butane-1, 3-diol (ii) Acetone to tert. butyl alcohol (iii) Benzoic acid to m-nitro benzoic acid (3)

Sample Question Paper for Class XII

Chemistry (Code-A)

(b) Give one example each of

[2]

(i) Clemmensen reduction (ii) Cannizzaro reaction OR (a) Carry out the following conversions:

[3]

(i) Ethanal to butan-1-ol (ii) Benzaldehyde to 3-phenyl propanol (iii) Ethyl benzene to benzene (b) Give one example each of

[2]

(i) Aldol condensation (ii) HVZ reaction 29. (a) At what pH of HCl solution will the standard hydrogen electrode have a potential – 0.118 V at 298 K?

[2]

(b) Write the equations of the reactions involved at each electrode in a H2 – O2 fuel cell.

[2]

(c) Why does the potential of a mercury cell remain constant?

[1]

OR (a) Calculate the equilibrium constant and work done by the cell

[2]

Ni + Cu2+  Ni2+ + Cu, given Eo 2   0.25 V Eo 2  0.34 V Ni /Ni Cu /Cu (b) Write the equations of the reactions involved at each electrode during the electrolysis of

[2]

(i) CuSO4(aq) using inert electrode (ii) Dilute solution of sulphuric acid (c) How many coulombs of electricity are needed for the conversion of 9 grams of Al form molten AlCl3? (Atomic mass of Al = 27) [1] 30. Police usually disperse the indisciplined mob by using tear gas shell. One of the person in the mob advised the people either to use water wetted cloth on eyes or to avoid smoke. (i) Write the chemical formula of tear gas.

[1]

(ii) Write the value involved as advised by the person present in the mob.

[2]

(iii) Write IUPAC name of tear gas.

[2] OR

Arrange the following in order of property indicated: (i) F2, Cl2, Br2, I2 – Increasing bond dissociation enthalpy (ii) HF, HCl, HBr, HI – Increasing acid strength (iii) NH3, PH3, AsH3, SbH3 – Increasing base strength (iv) H2O, H2S, H2Se, H2Te – Increasing boiling point (v) HF, HCl, HBr, HI – Increasing boiling point

   (4)

Chemistry (Code-A)

Solutions of Sample Question Paper for Class XII

Chemistry (Theory) - Class XII (Code-A) SOLUTIONS SECTION-A 1. 3-Bromo-5-fluoro-3, 5-dimethylheptane 2. (i) It is a zero order reaction. [R]0 2K 3. Out of the five electron pairs around the central Br-atom, the two lone pairs are at equatorial positions to minimise the repulsive interactions. Hence, BrF3 has T-shaped structure.

(ii) t1/ 2 

F

F

Br

F 4. Dispersed phase – milk fats Dispersion medium – water 5. Number of A-atoms per unit cell 

1  8(corners)  1 8

Number of B-atoms per unit cell  6 

1 3 2

Hence, the formula of the compound is AB3. 6.

AB

aq.    

A– (aq.) +

B+ (aq.)

Initially

1

0

0

At equilibrium

0.5

0.5

0.5

van’t Hoff factor  1    1.5 7. NaCN is used as a depressant for ZnS and prevents it from coming with froth. 8. 6XeF4 + 12H2O  4Xe + 2XeO3 + 24HF + 3O2

SECTION-B 9. The structural formula of 4-methylpent-3-en-2-one is

H3C — C — CH

CH3

—

O

C — CH3

O Due to the presence of H3C — C — group, it will respond positive to iodoform test. (1)

Solutions of Sample Question Paper for Class XII

Chemistry (Code-A)

10. Osmotic pressure may be defined as the excess pressure which must be applied to the solution side to just prevent the osmosis. Osmotic pressure is directly proportional to temperature as well as pressure. 11. 2Cu2S + 3O2  2Cu2O + 2SO2 Cu2S + 2Cu2O  6Cu + SO2 12. The two components of starch are amylose and amylopectin. Amylose is a linear polymer of -D-(+)-Glucose while amylopectin is heavily branched polymer of -D(+)-Glucose. O HI/P Reduction

13. (a) H—C — (CHOH)4 — CH2 — OH  CH3CH2CH2CH2CH2CH3

—

CHO

—

CHO

n-Hexane

—

—

(b) (CHOH)4 + 5(CH3CO)2O  (CHOCOCH3)4 + 5CH3COOH

CH2OH

CH2OCOCH3

Glucose

Pentacetyl glucose

14. H2SO4  H+ :OSO3H

—

H + H3C — CH2 — O – H + H+ H3C —CH2 — O — H Slow

+ H3C — CH2 + H2O

—

—

H

—

H



Fast H C = CH + H SO H — C — C — H + :OSO3H  2 2 2 4

H 15. (a) Hofmann’s Bromamide reaction: O Heat

H3C — C — NH2 + Br2 + 4KOH  H3C – NH2 + 2KBr + K2CO3 + 2H2O

CO

NK CO

CO

—

C2H5–I  –KI

—

—

CO

N — CH2CH3 CO H+/H2O —

NH

KOH(alc.)  –H2O

—

CO

—

—

(b) Gabriel phthalimide reaction:

COOH + H3C — CH2 — NH2 COOH

(2)

Chemistry (Code-A)

Solutions of Sample Question Paper for Class XII

16. (a) Distinction can be made by Lucas reagent. Treat both the solutions separately with Lucas reagent which is a mixture of HCl(g) and anhy. ZnCl2. The compound that shows turbidity instantly is 2-methylpropan-2-ol while the solution that shows turbidity after 5 minutes of heating, is Butan-1-ol. (b) Distinction can be made by litmus test. Add a few drops of blue litmus separately to the solutions of both the compounds. The solutions which changes the colour of the blue litmus to red is that of phenol while the other is benzyl alcohol. 17. (a) Aniline does not undergo Friedel Crafts reaction. It being a Lewis base, coordinates with anhy. AlCl3.

—

H2N  AlCl3

The amino group now, is not in a position to activate the benzene ring towards electrophilic substitution, that is alkylation or acylation. Also, AlCl3 does not remain free to generate the carbonation from alkyl or acyl halide. (b) The –NH2 group over benzene ring makes it so electron-rich site that Br2 molecule itself gets polarized under its influence. This helps in the generation of the electrophile Br+, even in the absence of a halogen carrier. OR (a) During acylation aniline gives CH 3 – C – NH

, which is a resonance stabilized compound.

O

(b) 3°-amine does not contain replaceable hydrogen on N-atom. 18. The solution of acetone and chloroform will show negative deviation from their ideal behaviour.

Cl

(+)

(–)

CH3

Cl–C–H..........O=C Cl

CH3

There is formation of hydrogen bond between acetone and chloroform molecules, so the escaping tendency of both components is lowered.

SECTION-C 19. We know that,  

z 

zM N A  a3

, here ‘a’ is edge length

6.23  6.023  1023  (4.00  108 )3  4.002  4 60

 The cubic unit cell is ‘face-centered cubic’. (3)

Solutions of Sample Question Paper for Class XII

Now, in fcc lattice, r  

Chemistry (Code-A)

a 2 2

4  108 2 2

= 1.414 ×10–8 cm 20. (a) Terylene is a condensation polymer and its monomers are Ethylene glycol (HOCH2CH2OH) and terephthalic acid HOOC

COOH

(b) Teflon is an addition polymer and its monomer is tetrafluoroethylene (CF2 = CF2) CH 3

(c) Its monomer unit is isoprene i.e., CH 3–C=CH–CH 3 21. (a) These two compounds are ionization isomers to each other and on treating the aq. solutions of the two with AgNO3(aq), [CO(NH3)5(SO4)]Br gives yellow ppts. of AgBr while the other compound does not. (b) The electronic configuration of Fe(Z = 26) is [Ar], 3d6, 4s2 while that of Fe(II) is [Ar], 3d6 since F– is a weak field ligand that does not cause pairing up of electrons, sp3d2 hybridization takes place. 4–

[FeF6] : 3d

4s

4p 3

4d 2

sp d hybridization The structure of the complex is octahedral and it is a high-spin complex. On the other hand, CN– is a strong field ligand that causes greater crystal field splitting and hence, pairing up of electrons. 4–

[Fe(CN)6] : 3d

4s

4p

d2sp3 This way, d2sp3 hybridization takes place and the octahedral structure is diamagnetic. 22. (a)

Physisorption

Chemisorption

(i) The adsorbate molecules (i) Adsorbate molecules are are held to the surface of held to the surface of adsorbent by weak van adsorbent by strong der Waals forces. chemical forces (chemical bonds). (ii) It is not specific in nature. (ii) It is highly specific. (iii)It forms multimolecular (iii) It forms monomolecular layers. layers.

(4)

Chemistry (Code-A)

Solutions of Sample Question Paper for Class XII

Lyophilic sol

(b)

Lyophobic sol

(i) When dispersion medium likes dispersed phase, the sol is called lyophilic.

(i) When dispersion medium dislikes dispersed phase, the sol is called lyophobic.

(ii) They are quite stable and (ii) They are easily precipitated are not precipitated easily. by addition of a small amount of a suitable electrolyte. (iii) They are reversible in nature.

(iii) They are reversible in nature.

23. (a) ICl is polar due to electronegativity difference between I and Cl. But I2 is nonpolar covalent compound. So stability of polar bond is less than covalent bond and ICl is more reactive than I2.

1 odd electron (incomplete octet of N)

N O

O

O

O

(b)

(Complete octet of N)

N—N

O O At lower temperature NO2 is converted into N2O4 due to incomplete octet of N in NO2. (c) In H3PO3, oxidation number of P is +3 and in H3PO4, P present in higher oxidation number +5, so H3PO4 is not further oxidised.

O F

F

Xe 24. (a)

F

F 3

2

sp d , Square pyramidal F F

P

F

(b)

Triangular bipyramidal

F F

(c)

O H

S O

O O

O

S O

H O

O

3

sp -Hybridised Sulphur (5)

Solutions of Sample Question Paper for Class XII

Chemistry (Code-A)

OR (a) Ca 3P2 + 6H 2O  3Ca(OH) 2 + 2PH 3 Cal. Phosphate

Phosphine

(b) XeF6 + NaF  Na+[XeF7]– [Sodium heptafluoroxenate (vi)] (c) Cu + 2H2SO4(conc.)  CuSO4 + SO2 + 2H2O 25. KP = Ae–EP/RT ; P  Presence of catalyst KA = Ae–EA/RT ; A  Absence of catalyst KP  e(EP E A )/RT  e E/RT KA KP E EA   A Ine   log10 10 KA RT 2.303RT  (45  55)  KP  (EP  E A )   Antillog    Antilog  2.303R300K  KA 2.303RT    

KP 10  Antilog  1.003 KA 2.303  8.314  300 KP  K A –

26. (a) KCN is ionic compound and generate CN ion in solution, the attack takes place mainly through carbon atom due to C — C bond strength is higher than C – N bond strength. (b) Resonating structure of chlorobenzene

CI

—



CI

— —



CI

— —



CI

— —

—

CI

Lone pair of Cl is conjugated with double bonds of ring. So the electron density of ortho and para positions increases by resonance and it undergoes electrophilic substitution at ortho and para positions while Cl is deactivating group.  Nu (c) CH2 = CH – CH2 – Cl  CH2 = CH – CH2 + Cl Allyl Chloride

Allyl (more stable carbocation by resonance)

 Nu CH3 – CH2 – CH2 – Cl  CH3 – CH2 – CH2 + Cl n-Propylchloride

1° carbocation

Intermediate allyl carbocation is more stable than 1° carbocation. So the allyl chloride is more reactive towards nucleophilic substitution. (6)

Chemistry (Code-A)

Solutions of Sample Question Paper for Class XII

27. Deficiency diseases by vitamin – A  Xerophthalmia, Night blindness C  Scurvy (Bleeding gums) Vitamin-A  Retinol Vitamin-C  Ascorbic acid

SECTION-D O

28. (a) (i)

O

OH

O

OH

Aldol

CH3 — CH + CH2 — CH  CH3 — CH — CH2 — CH  CH3 — CH — CH2 LiAlH4

(Condensations) Ba(OH)2

H

CH2 — OH Butan-1-3-diol

CH3

O H2O

(ii) CH3 — C — CH3 + CH3 — Mg — I  CH3 Acetone

OMgI  CH3 — C — OH –Mg(OH)I

Methyl

C

Mag. Iodide

CH3

CH3

CH3

tert-butyl alcohol

Adduct

COOH

COOH (Conc.) ( HNO3 + H2SO 4)



(iii)

NO2 Meta ntiro benzoic acid

Benzoic Acid (b) (i) Clemmensen reduction Zn–Hg

CH3 — CHO + 4[H]  CH3 — CH3 + H2O  Ethanal Ethane (ii) Cannizzaro reaction  2HCHO + NaOH  CH3 OH + HCOONa Formaldehyde

Methanol

OR (a) (i) Zn–Hg (Conc. HCl)

Na

Cl2/U.V.

CH3 — CH  CH3 — CH3  CH3 — CH2 — Cl  CH3 — CH2 — CH2 — CH3 O

Clemmenson reduction

Ethane

Mono Chlorination

Wurtz Reaction

Cl2/U.V.

Ethanal (i) B2H6,THF

CH3 — CH2 — CH2 — CH2  CH3 — CH2 — CH = CH2CH3 — CH2 — CH — CH3 (ii) H O /OH –

2

Butan-1-ol

(CH3)3COK

2

Cl

OH

(7)

Solutions of Sample Question Paper for Class XII

Chemistry (Code-A)

HO – CH2 CHO

COOH KMnO4 [O]

(ii)

CH2 – CH = CH2 NaOH



 CaO

 AlCl Cl – CH2 – CH = CH2 3

Benzaldehyde

 HO B2H6, THF 2

2

3-Phenyl Propanol

CH2 – CH3

COOH

Baeyer’s reagent KMnO4

(ii.i)

CH2 – CH2

Soda Lime NaOH + CaO



 Decarboxylation

Ethyl Benzene

Benzoid Acid

Benzene

(b) (i) Aldol condensation

O

OH

OH Ba(OH)2

CH3 — CH + CH2 — CHO  CH3 — CH — CH2 — CHO Ethanal Aldol (ii) HVZ reaction

Br O O Br2/P Br2/P Br2/P CH3 — C — OH  CH2 — C — OH  CH — C — OH    Br Br O

29. (a) H+ + e–  H2(g) Ecell = –

pH2 0.0591  log 1 H   

or –0.118 = –

0.0591 1  log 1 H   

 [H+] = 10–2 mol/L  pH = 2 (b) At anode

H2(g)  2H + 2e +

–

At cathode

2H+ + 2e– +1/2 O2(I)  H2O(l)

Net reaction

H2(g) +1/2 O2(g)  H2O(l) (8)

O CBr2 — C — OH

Chemistry (Code-A)

Solutions of Sample Question Paper for Class XII

(c) Anode  Zn–Hg Cathode  Carbon Paste

Mercury cell

Overall reaction, Zn(Hg) + HgO(s)  ZnO(s) + Hg(l) 0

E = 1.35 V

In the final equation of reaction, no solvent or ion is involved therefore, the emf does not drop easily. OR (a) E°cell = E°cathode – E°anode = 0.34 – (–0.25) = 0.59 V  G° = –2 × 96500 × 0.59 J = –113870 J = –113.9 kJ Now, G° = –2.303 RT log KC  logKC =

–113900 = 19.96 –2.303  8.314  298

 KC = antilog (19.96)  KC  1020 (b) (i) At cathode Cu+2(aq) + 2e–  Cu(s) At anode

OH (aq)  OH + e

–

4OH  2H2O + O2 (ii) 2H 2SO 4

2H + + 2HSO 4

At anode 2HSO 4  H2S 2O 8 + 2e – H2S2O8 + H2O  2H2SO 4 + ½ O2

At cathode

2H  + 2e–  H 2 Net reaction Electric H2O  H2 +1/2 O2 Current

(9)

Solutions of Sample Question Paper for Class XII

Chemistry (Code-A)

(c) W = ZQ Q

W W 9   96500   96500 Z E 9

Q  96500 coulomb

Cl 30. (i) Cl – C – NO2 .

Cl Which is also called as tear gas. When it reaches in eye it irritates gland and brings tears. (ii) Social responsibility and social justice. (iii) 1, 1, 1 Trichloro-1-nitromethane OR

(i) I2 < F2 < Br2 < Cl2 : Increasing bond dissociation energy (ii) HF < HCl < HBr < HI : Increasing acid strength (iii) SbH3 < AsH3 < PH3 < NH3 : Increasing base strength (iv) H2S < H2Se < H2Te < H2O : Increasing boiling point (v) HCl < HBr < HI < HF : Increasing boiling point



(10)