SAMPLE QUESTION PAPER

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Chemistry (Code-A) Sample Question Paper for Class XII

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..

SAMPLE QUESTION PAPER

Chemistry (Theory) - Class XII (Code-A)

SECTION-A

Very Short Answer Type Questions : [8 × 1 = 8]

1. Give IUPAC name of the compound: [1]

CH — C — CH — C — CH3 2 3 — F — C H2 5 — C H2 5 — Br

2. Consider the reaction R  P. The change in the concentration of R with time is shown in the following

plot. [1]

Time [R]t

(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]

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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 : [9 × 3 = 27]

19. 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. (N_A = 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

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Chemistry (Code-A) Sample Question Paper for Class XII

21. (a) Name the isomerism exhibited by the following pair of coordination compounds: [3] [Co(NH₃)₅Br]SO₄ & [Co(NH₃)₅SO₄]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

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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}

2 2

o o

Ni /Ni Cu /Cu

E   0.25 V E  0.34 V

(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

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Chemistry (Code-A) Solutions of Sample Question Paper for Class XII

SECTION-A

1. 3-Bromo-5-fluoro-3, 5-dimethylheptane

2. (i) It is a zero order reaction. (ii) 1/ 2 0

[R] t

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.

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

H C — C — CH C — CH3 3

O

—

CH3

Due to the presence of H C — C — 3 O

group, it will respond positive to iodoform test.

Chemistry (Theory) - Class XII (Code-A)

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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.

13. (a) H—C — (CHOH) — CH — OH 4 2  CH CH CH CH CH CH3 2 2 2 2 3

O

Reduction HI/P

n-Hexane

(b) _{(CHOH) + 5(CH CO) O} _{(CHOCOCH ) + 5CH COOH}

4 3 2  3 4 3 — — CH OH2 Glucose CHO — — CH OCOCH2 3 Pentacetyl glucose CHO 14. _{H SO}₂ ₄__{H+ :OSO H}₃ H C — CH — O – H + H3 2 H C —CH — O — H3 2 + —+ H Slow H C — CH + H O3 2 2 + H — C — C — H + :OSO H 3  H C = CH + H SO2 2 2 4 — — H H — H  Fast

15. (a) Hofmann’s Bromamide reaction:

H C — C — NH + Br + 4KOH 3 2 2  H C – NH + 2KBr + K CO + 2H O3 2 2 3 2

Heat

O

(b) Gabriel phthalimide reaction:

—CO CO — NH KOH(alc.) –H O2 —CO CO — NK C H –I2 5 –KI —CO CO — N — CH CH2 3 H /H O+ 2 —COOH COOH + H C — CH — NH3 2 2

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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.

—

H N 2 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 – C – NH3

O

, which is a resonance stabilized compound.

(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–C–H...O=C Cl

Cl

(+) (–) CH3 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, ₃ A z M , N a   

 here ‘a’ is edge length

23 8 3 6.23 6.023 10 (4.00 10 ) z 4.002 4 60         

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Solutions of Sample Question Paper for Class XII Chemistry (Code-A) Now, in fcc lattice, r a 2 2  8 4 10 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)

(c) Its monomer unit is isoprene i.e., CH –C=CH–CH3 3

CH3

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_{, 4s}2_{while that of Fe(II) is [Ar], 3d}6_{since F}–_{is a}

weak field ligand that does not cause pairing up of electrons, sp3_d2_{hybridization takes place.}

[FeF ] :6 4–

3d 4s 4p 4d

sp d3 2

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.

[Fe(CN) ] :6 4–

3d 4s 4p

d sp2 3

This way, d2_sp3_{hybridization takes place and the octahedral structure is diamagnetic.}

22. (a)

(i) The adsorbate molecules are held to the surface of adsorbent by weak van der Waals forces.

(ii) It is not specific in nature. (iii)It forms multimolecular

layers.

(i) Adsorbate molecules are held to the surface of adsorbent by strong chemical forces (chemical bonds).

(ii) It is highly specific.

(iii) It forms monomolecular layers.

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(b)

(i) When dispersion medium likes dispersed phase, the sol is called lyophilic. (ii) They are quite stable and are not precipitated easily.

(iii) They are reversible in nature.

Lyophilic sol Lyophobic sol

(i) When dispersion medium dislikes dispersed phase, the sol is called lyophobic. (ii) They are easily precipitated by addition of a small amount of a suitable electrolyte.

(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.

(b)

N 1 odd electron (incomplete octet of N)

O N — N O O O (Complete octet of 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.

24. (a) F F F F Xe O sp d3 2, Square pyramidal (b) F F F P F F Triangular bipyramidal (c) S _O H O S O O O O O O H sp3 -Hybridised Sulphur

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Solutions of Sample Question Paper for Class XII Chemistry (Code-A)

OR

(a) Ca P + 6H O 3 2 2  3Ca(OH) + 2PH2 3

Cal. Phosphate Phosphine

(b) XeF + NaF 6  Na [XeF ] [Sodium heptafluoroxenate (vi)]7

+ –

(c) Cu + 2H₂SO₄(conc.)  CuSO₄ + SO₂ + 2H₂O 25. K_P = Ae–E_P/RT _; P  Presence of catalyst

K_A = Ae–E_A/RT _{; A}_{ Absence of catalyst}

P A (E E )/RT E/RT P A K e e K      P A A 10 A K E E Ine log 10 K  RT  2.303RT P P A A K (E E ) (45 55) Antillog Antilog K 2.303RT 2.303R300K          _ _ _ _     P A K 10 Antilog 1.003 K  2.303 8.314 300   P A K K

26. (a) KCN is ionic compound and generate C–N 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.

(c) _{CH = CH – CH – Cl} _{CH = CH – CH + Cl}

2 2  2 2

Allyl Chloride Allyl (more stable carbocation by resonance)

Nu 

CH – CH – CH – Cl 3 2 2  CH – CH – CH + Cl3 2 2

n-Propylchloride 1° carbocation

Nu 

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

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27. Deficiency diseases by vitamin – A  Xerophthalmia, Night blindness C  Scurvy (Bleeding gums)

Vitamin-A  Retinol Vitamin-C  Ascorbic acid

SECTION-D

28. (a) (i) CH — CH + CH — CH 3 2  CH — CH — CH — CH 3 2  CH — CH — CH 3 2 O H O Aldol (Condensations) Ba(OH)2 OH O LiAlH4 OH CH — OH2 Butan-1-3-diol (ii) CH — C — CH + CH — Mg — I 3 3 3  CH 3  CH — C — OH 3 O C CH3 CH3 OMgI –Mg(OH)I H O2 CH3 CH3 Acetone Methyl Mag. Iodide Adduct tert-butyl alcohol (iii) COOH ( HNO + H SO )3 2 4 COOH NO2

Benzoic Acid Meta ntiro benzoic acid

(Conc.)

(b) (i) Clemmensen reduction

CH — CHO + 4[H] 3  CH — CH + H O3 3 2

Zn–Hg 

Ethanal Ethane

(ii) Cannizzaro reaction

2HCHO + NaOH  CH OH + HCOONa3

Formaldehyde Methanol  OR (a) (i) CH — CH 3  CH — CH 3 3 CH — CH — Cl 3 2  CH — CH — CH — CH3 2 2 3 Ethanal Clemmenson reduction Ethane Mono Chlorination Wurtz Reaction O Zn–Hg (Conc. HCl) Cl /U.V.2 Na Cl /U.V.2 CH — CH — CH — CH 3 2 2 2CH — CH — CH = CH3 2 2CH — CH — CH — CH3 2 3 Cl (CH ) COK3 3 (i) B H ,THF2 6 (ii) H O /OH2 2 – Butan-1-ol OH

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Solutions of Sample Question Paper for Class XII Chemistry (Code-A) (ii) CHO Benzaldehyde [O] KMnO4 COOH NaOH CaO  Cl – CH – CH = CH2 2 AlCl3 CH – CH = CH₂ ₂ B H , THF2 6 H O2 2 CH – CH₂ ₂ HO – CH2 3-Phenyl Propanol (ii.i) CH – CH2 3 Ethyl Benzene  Baeyer’s reagent KMnO4 COOH Benzoid Acid  Soda Lime NaOH + CaO Decarboxylation Benzene

(b) (i) Aldol condensation

CH — CH + CH — CHO 3 2  CH — CH — CH — CHO3 2 O Ba(OH)2 OH Ethanal Aldol OH (ii) HVZ reaction CH — C — OH 3  CH — C — OH 2  CH — C — OH O  Br /P2 Br O Br /P2  Br Br O Br /P2  CBr — C — OH2 O 29. (a) H+_{+ e}– H 2(g) E_cell = –0.0591 logpH2 1  _H   or –0.118 = –0.0591 log 1 1  _H_  [H+_{] = 10}–2_mol/L  pH = 2 (b) _{At anode H (g)} _{2H + 2e}

At cathode 2H + 2e +1/2 O (I) H O(l) Net reaction 2 2 2   + – + – H (g) +1/2 O (g) 2 2  H O(l)2

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(c) Anode Zn–Hg

Cathode Carbon Paste



 Mercury cell

Overall reaction,

E = 1.35 V0

Zn(Hg) + HgO(s)  ZnO(s) + Hg(l)

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 K_C  logK_C = –113900 –2.303 8.314 298  = 19.96  KC = antilog (19.96)  K_C  1020 (b) (i) At cathode Cu+2_{(aq) + 2e}–  Cu(s) At anode OH (aq)  OH + e– 4OH  2H₂O + O₂ (ii) 2H SO 2H + 2HSO2 4 4 + At anode 2HSO 4 H S O + 2e2 2 8 – H S O + H O 2 2 8 2  2H SO + ½ O2 4 2 At cathode 2H + 2e  – H2 Net reaction H O 2  H +1/2 O2 2 Electric Current

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Solutions of Sample Question Paper for Class XII Chemistry (Code-A) (c) W = ZQ W W 9 Q 96500 96500 Z E 9      Q96500 coulomb 30. (i) Cl – C – NO2 Cl 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