Sample Paper Annual Examination. Class -XIIA. Subject-CHEMISTRY

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Sample Paper – Annual Examination

Class -XIIA

Subject-CHEMISTRY

Read the following instructions carefully.

a) There are 33 questions in this question paper. All questions are compulsory. b) Section A: Q. No. 1 to 16 are objective type questions. Q. No. 1 and 2 are

passage-based questions carrying 4 marks each while Q. No. 3 to 16 carry 1 mark each. c) Section B: Q. No. 17 to 25 are short answer questions and carry 2 marks each. d) Section C: Q. No. 26 to 30 are short answer questions and carry 3 marks each. e) Section D: Q. No. 31 to 33 are long answer questions carrying 5 marks each. f) There is no overall choice. However, internal choices have been provided. g) Use of calculators and log tables is not permitted.

SECTION A (OBJECTIVE TYPE)

1. Read the passage given below and answer the following questions: (1x 4 = 4)

Oxidation of alcohols to aldehydes is partial oxidation; aldehydes are further oxidized to carboxylic acids. Conditions required for making aldehydes are heat and distillation. In aldehyde formation, the temperature of the reaction should be kept above the boiling point of the aldehyde and below the boiling point of the alcohol.

Reagents useful for the transformation of primary alcohols to aldehydes are normally also suitable for the oxidation of secondary alcohols to ketones.

The following questions are multiple choice questions. Choose the most appropriate answer:

(i) Which of the following alcohols can be obtained from HCHO? a) Methanol

b) Ethanol c) Propanol d) All of these

(ii) Ethanol can be converted into ethanal by: a) Catalytic hydrogenation

b) Treatment with LiAlH4

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d) Treatment with KMnO4

OR

(ii) The compound that gives a tribromo derivative on treatment with bromine water is: a) m-Cresol

b) Benzyl alcohol c) o-Cresol d) p-Cresol

(iii) Which of the following species can act as the strongest base? a) Hydroxide

b) Alkoxide c) Phenoxide

d) m-Nitro phenoxide

(iv) Arrange the following compounds in increasing order of boiling point: Propan-1-ol, butan-1-ol, butan-2-ol, pentan-1-ol.

a) Propan-1-ol, butan-2-ol, butan-1-ol, pentan-1-ol b) Propan-1-ol, butan-1-ol, butan-2-ol, pentan-1-ol c) Pentan-1-ol, butan-2-ol, butan-1-ol, propan-1-ol d) Pentan-1-ol, butan-1-ol, butan-2-ol, propan-1-ol

Read the passage given below and answer the following questions: (1 x 4 = 4)

The foundation of colloidal chemistry was laid down by an English chemist, Thomas Graham in 1861. Various others such as Tyndall, Hardy and many more contributed to the advancement in the field. The colloidal phenomenon invented by Tyndall sketched the line of distinction between a true and a colloidal solution. The same phenomenon is encountered in a dark room and dense canopy of trees found in forests.

Colloidal particles always carry an electric charge which may be either positive or negative. For example, when AgNO3 solution is added to KI solution, negatively charged

colloidal sol is obtained. The presence of equal and similar charges on colloidal particles provide stability to the colloidal sol and if, somehow, charge is removed, coagulation of sol occurs. Lyophobic sols are readily coagulated as compared to lyophilic sols.

2. In these questions, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.

(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.

(b) Assertion and reason both are correct statements but reason is not the correct explanation for assertion.

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m 2 4 3 4

(d) Assertion is wrong statement but reason is correct statement.

(i) Assertion: Colloidal solutions do not show Brownian movement.

Reason: Brownian motion is responsible for stability of sols.

(ii) Assertion: Scattering of light illuminates the path of beam in the colloidal dispersion.

Reason: Colloidal solutions as well as true solutions show Tyndall effect.

(iii) Assertion: Ba2+ is more effective than Na+ in carrying out the coagulation of a negative sol.

Reason: The greater the valency of the flocculating ion added, the greater is its

power to cause precipitation.

(iv) Assertion: Lyophobic sols are more stable than lyophilic sols.

Reason: Lyophilic colloids are extensively solvated. OR

(iv) Assertion: When KI solution is added to AgNO3 solution, positively charged

colloidal sol is obtained.

Reason: Positive charge is due to the preferential adsorption of ions.

Following questions (3-11) are multiple choice questions carrying 1 mark each: 3. The value of λ0 _{of Al (SO ) is 858 S cm}2 _mol-1_{, while limiting ionic conductivity of SO}

2-is 160 S cm2 _mol-1_{. The limiting ionic conductivity of Al}3+_is: (a) 698 S cm2 _mol-1

(b) 189 S cm2 _mol-1 (c) 378 S cm2 _mol-1 (d) 349 S cm2 _mol-1

4. Which of the following reactions of glucose cannot be explained by its open

chain structure?

a) Glucose is oxidised by Br2(aq) to gluconic acid

b) Glucose reacts with acetic anhydride to form pentaacetate derivative c) Glucose does not react with 2,4-DNP

d) Glucose is reduced to n-hexane on reaction with hydrogen iodide OR

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4. Nucleotide units in a nucleic acid are linked through .

a) Glycosidic linkage b) Phosphodiester linkage c) Peptide linkage

d) Heterocyclic bases

5. If two substances A and B have P0A : P0B = 1:2 and have mole fraction in solution 1:2,

then mole fraction of A in vapours is a) 0.33

b) 0.25 c) 0.52 d) 0.2

6. Lanthanide contraction is caused due to

a) appreciable shielding effect offered by 4f electrons b) appreciable shielding effect offered by 5d electrons c) some effective nuclear charge from Ce to Lu d) poor shielding effect offered by 4f electrons

OR

6. Which of the following is a diamagnetic ion? a) V2+

b) Sc3+ c) Cu2+

d) Mn3+

7. Trichloroacetaldehyde was subjected to Cannizzaro’s reaction by using NaOH. The mixture of the products contains sodium trichloro acetate ion and another compound. The other compound is:

a) 2,2,2-Trichloro ethanol b) Trichloro methanol c) 2,2,2-Trichloropropanol d) Chloroform

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7. Which of the following alkyl halides is most suitable for alkylation of ethyl amine through SN1 mechanism

a) Bromo ethane b) Bromo benzene c) Benzyl bromide

d) 2-Bromo-2-methyl propane

8. Which response gives the correct coordination number and oxidation number of the transition metal atom in [Co(NH3)2(H2O)2Cl2]+ ?

a) C.N = 3; O.N = +1 b) C.N = 4; O.N = +2 c) C.N = 6; O.N = +1 d) C.N = 6; O.N = +3

OR

8. The correct IUPAC name of the complex: [FeF4(OH2)2]- is

a) diaquairon(III)tetraflourate(III)ion b) diaquatetraflouroferrate(III)ion c) diaquatetraflouroiron(III)ion d) tetraflourodihydroxyferrate(III)ion

9. Which of the following has the maximum number of unpaired electrons? a) Fe2+

b) Cr3+

c) Fe3+

d) Co2+

10. In the chemical reaction of diazotisation of aniline to form product A, followed by treatment with fluoroboric acid to form product B, the compounds A and B respectively are a) Benzene diazonium chloride and Nitrobenzene

b) Nitrobenzene and Fluorobenzene

c) Phenol and Benzene diazonium chloride

d) Benzene diazonium chloride and fluorobenzene

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In the following questions (Q No. 12-16), a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.

(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.

(b) Assertion and reason both are correct statements but reason is not the correct explanation for assertion.

(c) Assertion is correct statement but reason is wrong statement. (d) Assertion is wrong statement but reason is correct statement.

12. Assertion: Thymine pairs with adenine whereas cytosine pairs with guanine in the DNA molecule. Reason: The hydrogen bonding between bases of two strands is highly specific. 13. Assertion: On moving down in group 16, the thermal stability of hydrides decreases

from H2O to H2Po

Reason: The bond (H – E) dissociation enthalpy decreases down the group

14. Assertion: To avoid bends, the tanks used by scuba divers are filled with air diluted with helium. Reason: Helium is very less soluble in blood even at high pressure.

OR

14. Assertion: The solutions, which show a large positive deviation from Raoult’s law form maximum boiling azeotrope at a specific composition.

Reason: Ethanol-water mixture containing 95% ethanol by volume form minimum boiling azeotrope.

15. Assertion: Formaldehyde is a planar molecule.

Reason: The carbonyl carbon of formaldehyde lies in sp2 hybrid state. 16. Assertion: Phenetole on cleavage with HI yields phenol and ethyl

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SECTION B

The following questions, Q. No 17-25 are short answer type and carry 2 marks each.

17. Draw the structures of the optically active unsaturated compound having molecular formula C5H9Br, that after addition of hydrogen becomes either optically inactive or

shows optical activity. Explain.

OR 17. Convert in not more than two steps:

a) Propene to Propyne

b) Ethyl benzene to 2-Phenyl propanamide

18. Vapour pressure of water at 293K is 17.535mm of Hg. Calculate the vapour pressure of water at 293K when 25g of glucose is dissolved in 450g of water.

19. (i) Explain: [Fe(H2O)6]3+ is more paramagnetic than [Fe(CN)6]

3-(ii) Write the IUPAC name of the coordination complex: [CrCl2(en)2]Cl

OR

19. Give the electronic configuration of d-orbitals of K3[Fe(CN)6] and K3[FeF6] and

explain why these complexes give different colours with the same solution? 20. A reaction is first order in A and second order in B.

(i) Write the differential rate equation.

(ii) How is the rate affected when the concentration of both A and B are doubled?

OR

20. The following results have been obtained during the kinetic studies of the reaction: 2A + B → C + D

Experiment A / mol L-1 B / mol L-1 Initial rate of formation of D / mol L-1

1 0.1 0.1 6.0 x 10-3

2 0.3 0.2 7.2 x 10-2

3 0.3 0.4 2.88 x 10-1

4 0.4 0.1 2.40 x 10-2

Determine the rate law and rate constant for the reaction.

21. A first order reaction takes 23.1 minutes for 50% completion. Calculate the time required for 75% completion of this reaction.

(log 2 = 0.301, log 3 = 0.477, log 4 = 0.6021) 22. Write one chemical reaction each to illustrate the following:

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(i) Reimer-Tiemann reaction

(ii) Williamson’s synthesis to obtain anisole.

23. Give the formula and describe the structure of a noble gas species which is isostructural with BrO3 –.

24. Following compounds are given to you: 2- Bromo pentane, 2- Bromo-2-methyl butane, 1-Bromo pentane

(i) Write the compound which is most reactive towards SN2 reaction.

(ii) Write the compound which is optically active showing its chiral centre. (iii) Show the reaction of the compound which is most reactive towards

elimination reaction.

25. A sample of ferrous oxide has actual formula Fe0.93 O1.00. In this sample what

fraction of metal ions are Fe2+ _{ions? What type of non-stoichiometric defect is}

present in this sample?

SECTION C

Q.NO 26-30 are Short Answer Type II carrying 3 mark each.

26. Give reasons for the following:

a) Why is Cr2+ reducing and Mn3+ oxidising when both have d4 configuration b) E0 _{of Cu is + 0.34V while that of Zn is -- 0.76V. Explain.}

c) The lowest oxide of transition metal is basic whereas the highest oxide is amphoteric or acidic.

OR

26. Following are the transition metal ions of 3d series: Ti4+, V2+, Mn3+, Cr3+ Answer the following questions:

a) Which ion is most stable in an aqueous solution and why? b) Which ion is a strong oxidising agent and why?

c) Which ion is colourless and why?

27. 4-Nitro phenol reacts with Sn/HCl to form compound A which on further reaction with benzene diazonium chloride, at a pH of 9-10 forms compound B while the same reaction at a pH of 4-5 forms compound C. Identify A, B and C and give sequence of reactions., along with their IUPAC names.

OR 27. (i) Bring out the following conversions:

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b) Ethanamine to Methanamine

(ii) How does benzylamine and aniline react with nitrous acid at 0-50 C? Justify the reaction.

28. An element ‘X’ (At. Mass = 40g/mol) having fcc structure, has unit cell edge length of 400 pm. Calculate the density of ‘X’ and the number of unit cells in 4g of ‘X’.

29. (i) Amino acids behave like salts rather than simple amines or carboxylic acids. Explain.

(ii) Show the peptide linkage when alanine combines with glycine and glycine with alanine.

(iii) Draw structures to show the essential difference between α-form of glucose and β- form of glucose.

30. (a) Reducing character increases from HF to HI. Why?

(b) Arrange the hydrides of group 15 in increasing order of their basic nature. (c) Ozone is thermodynamically unstable. Account for the statement.

SECTION D

Q.No. 31 to 33 are long answer type carrying 5 marks each.

31. (a) Answer the following questions:

(i) Write the balance chemical reaction for reaction of zinc with dilute nitric acid (ii) Draw the shape of BrF5

(b) A colourless gas ‘A’ with a pungent odour is highly soluble in water and its aqueous solution is weakly basic. As a weak base it precipitates the hydroxides of many metals from their salt solution. Gas ‘A’ finds application in detection of metal ions. It gives a deep blue colouration with copper ions. Identify the gas ‘A’ and write the chemical equations involved in the following:

(i) Gas ‘A’ with copper ions

(ii) Solution of gas ‘A’ with zinc sulphate solution

OR

31. (a) Give reason to explain why ClF3 exist but FCl3 does not?

(b) With what neutral molecule is ClO- isoelectronic. Is that molecule a Lewis base? (c) On heating compound ‘A’ gives a gas ‘B’ which is a constituent of air. This gas

when treated with 3 moles of hydrogen in presence of a catalyst gives another gas ‘C’ which is basic in nature. Gas ‘C’ on further oxidation in moist condition gives a compound ‘D’ which is part of acid rain. Identify the compounds ‘A’ to ‘D’ and also give necessary equations of all steps involved.

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Cr /Cr Fe /Fe

32. (i) An alkene, A with molecular formula C7H14 on ozonolysis yields an aldehyde.

The aldehyde is easily oxidised to B. B when treated with bromine in the presence of red Phosphorous yields C, which on hydrolysis gives D. This acid can also be obtained from acetone by reaction of hydrogen cyanide in alkaline medium followed by hydrolysis. Identify A, B, C and D and write chemical reactions involved.

(ii) Carboxylic acids do not give reactions of aldehydes and ketones. Justify with structural explanation.

OR

32. (i) An organic compound A with molecular formula C5H8O2 is reduced to n-Pentane

on treatment with Zn/Hg-HCl(l). A forms a dioxime with hydroxyl amine and gives a positive iodoform test and Tollen’s test. Identify the compound A, deduce its structure and write chemical reactions involved.

(ii) Why are aldehydes more volatile than the corresponding alcohols? (iii) Name the reagent which converts But-2-ene-1-nitrile to But-2-enal.

(iv) Dialkyl cadmium is preferred over Grignard reagent for preparation of ketone. Why?

33. (a) State Kohlrausch law

(b) Calculate e.m.f. of the following cell at 298 K: 2Cr(s) + 3Fe2+ (0.1M) 2Cr3+ (0.01M) + 3Fe (s)E0 3+ = -0.74V, E0 2+

= -0.44V

OR

33. (a) Which reference electrode is used to measure the electrode potential of other electrodes?

(b) Molar conductance of a 1.5 M solution of an electrolyte is found to be 138.9 S Cm2. What would be the specific conductance of this solution?

(c) When acidulated water is electrolysed, will the pH of the solution be affected? Justify your answer.

(d) Write the Nernst equation for a Zn – Cu cell. How will the Ecell be affected