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SAMPLE PAPER -10 CLASS-XII SUB - CHEMISTRY Time Allowed: 3 Hrs Maximum Marks: 70 General Instructions: 1. All questions are compulsory. 2. Question No. 1-8 are very short answer questions and carry 1 mark each. 3. Question No. 9-18 are short answer questions and carry 2 marks each. 4. Question No. 19-27 are also short answer questions and carry 3 marks each. 5. Question No. 28-30 are long answer questions and carry 5 marks each. 6. Use log tables if necessary, use of calculators is not allowed. 1. Why is the bond dissociation energy of fluorine molecule less than that of chlorine molecule? 2. What is meant by shape selective catalysis? 3. Write the IUPAC name of CH3CO CH2CH=CH COOH. 4. Is optical isomerism possible in tetrahedral complex? Why? 5. What do you mean by order of reaction? 6. How are phenols much more acidic than alcohols? 7. What are reducing sugars? 8. Give the use of DDT, Freon 12 . 9. Aluminium crystallizes in a fcc closed packed structure. Its atomic radius is 12.5 pm. (a) What is the length of the edge of the unit cell? (b) How many such unit cells are there in a 2.00 m3 piece of aluminium. 10. Give reasons: (a)Aromatic amines are less basic than aliphatic amines. (b)Aniline does not undergo Friedel Crafts alkylation 11. (a) Write IUPAC name of the following: (i)K3 [Fe (C2O4)3] www.cpprashanthschemistry.com Page 1 (ii)Pt (NH3)6] Cl4. (b)What are ambidentate ligands ? Explain with example. 12. (a)Give the resonating structures of NO2 & N2O5 . (b)Complete the following reactions: (i) 4Al + 3O2 → (ii)C2H4 + O2 OR Write the steps involved in Contact’s process 13. For the reaction: NO2 (g) + CO2 (g) → CO2 (g) + NO(g) The proposed mechanism is as below: (a)NO2+NO2→NO+NO3 (slow) (b)NO3+CO→CO2+NO2 (fast) What is the rate law for the reaction? 14. How will you distinguish between: (a)(CH3)2NH & (CH3)3N (b)C6H5NH2 & CH3NH2 15. Account for the following observation: (a) Among the halogens, fluorine is the strongest oxidizing agent. (b) Acidity of oxoacids of chlorine is HOCl< HOClO<HOClO2 <HOClO3 16. Define ferro magnetism (ii) anti ferromagnetism 17. (a) Explain the terms strong and weak electrolyte. (b) Calculate the emf of the cell: Mg(s) /Mg2+ (0.1M)║Cu2+(1x10-3M)/ Cu(s) www.cpprashanthschemistry.com Page 2 18. The rate of a particular reaction doubles when temperature changes from 270C to 370C. Calculate the activation energy of such reaction. 19. Describe the following with suitable example: (a)Transquilizers (b) Preservatives (c) Analgesics. 20. (a) What are fuel cells? Write the electrode reaction of a fuel cell which uses the reaction of hydrogen with oxygen. (b) Write the formulation and the standard cell potential of the galvanic cell in which the following reaction takes place: Fe2+(aq)+ Ag+(aq) →Fe3+(aq) +Ag(s) 21. How are the following conversions carried out? (a) Phenol to acetophenone (b) Ethanol to 2-propanol 22. (a)Differentiate between roasting and calcinations. Explain with example. (b) Why is copper matte roasted in a reverberatory furnace lined inside with silica? 23. Which alkyl halide from the following pairs reacts more rapidly by SN2 mechanism? Explain it. (a) CH3-CH (CH3)-CH2CH2Br (I) or CH3CH2-CH (CH3)-CH2Br (II) (b)CH 3CH 2CH 2CH 2Br or CH 2CH 2CH(Br) CH3 (I) (c) CH3CH2CH(Br)CH3 (II) or CH3CH(CH3)2Br (I) (II) 24. (a)Explain the principle of electrodialysis. (b) In NH3 and CO2, which gas will be absorbed more rapidly on the surface of charcoal and why? (c)How are multimolecular colloids different from macromolecular colloids? www.cpprashanthschemistry.com Page 3 25. Differentiate between addition and condensation polymers based on mode polymerization. Give one example of each. OR Wite the monomers of i) PVC (ii) Teflon (iii) nylon-6 26. Give reasons (a) interhalogen compounds are more reactive than halogens. (b)PCl5 is known but NCl5 is not known. (c) Amongst all noble gases only xenon is known to form compounds with oxygen and fluorine. 27. Nita’s mother fell ill & doctor diagnosed her with pernicious anemia. She felt lethargic and her mother in household work till she recovered. i) ii) iii) Name the vitamin whose deficiency caused pernicious anemia. Name the sources which will provide this vitamin. Mention the values shown by Nita 28. (a) Assign reason for the following: (i)Transition metal ions are usually coloured. (ii) Transition elements exhibit variable oxidation state. (iii) Interstitial compounds are well known for transition metal. (b) Give balanced chemical equation of the two reactions in which KMnO4 acts as an oxidizing agent in acidic medium. OR Give reasons for the following: a) Transition metals have high enthalpies of atomization. b) Among the lanthanoids, Ce(III) is easily oxidised to Ce(IV). c) Fe3+/Fe2+ redox couple has less positive electrode potential than Mn3+/Mn2+couple. www.cpprashanthschemistry.com Page 4 d) Copper (I) has d10 configuration, while copper (II) has d9 configuration, still copper (II) is more stable in aqueous solution than copper (I). e) The second and third transition series elements have almost similar atomic radii. 29. (a) Account for the following: (i) Electrophilic substitution in benzoic acid takes place at meta position. (ii)Carboxylic acids have higher boiling points than alcohols of comparable molecular mass. (b)How will you bring about the following conversions? (i)Propanone to Propene (ii) Benzoic acid to Benzaldehyde (iii) Ethanol to 3-hydroxybutenal. OR a) How are the following preparations carried out? i) 2- Butenal from ethanal ii) Tert - Butyl alcohol from acetone b) Give the mechanism of HCN addition to acetaldehyde c) Write chemical equations to illustrate each of the following reaction: i) Acylation reaction ii) Rosenmund reaction 30. What is meant by Van’t Hoff factor? The osmotic pressure of 0.0103 molar solution of an electrolyte is found to be 0.70 atm at 270C. Calculate the Van’t Hoff factor. [R=0.082 Later mol-1K-1]. What conclusion do you draw about the molecular state of the solute in the solution? OR www.cpprashanthschemistry.com Page 5 a) Vapour pressure of CCl4 at 250C is 143 mm of Hg. 0.5g of a non volatile solute(molar mass 65)is dissolved in 100 ml CCl4. Find the vapour pressure of the solution.(Density of CCl4 = 1.58g/cm3) b) State Henry’s law. Give its two practical applications. SAMPLE PAPER -10 SCORING KEY www.cpprashanthschemistry.com Page 6 1. (a) Lower value of bond dissociation energy of F 2 is due to strong repulsion between the non bonding elements of F atom in F2 molecule.( 1) (b)Due to the absence of the d- orbitals, multiple bonding cannot occour(1). 2. Shape selective catalysis is a chemical reaction in which the rate depends on the pore size of catalyst and also on the shape and size of the reactant and product molecule(1). 3. 5-oxohex-2-enoicacid. (1). 4. No. because all 4 bonds are symmetrically placed and equivalents 5. Order of the reaction may be defined as “the sum of powers or exponents of the reactants in the rate of law expression (1). 6. Phenol is more acidic than alcohol because after losing H+ ion, it forms the phenoxide ion which is resonance stabilized. On the other hand, in methoxide ion, no resonance is possible (1). 7. All these carbohydrates which reduce the Fehling solution and Tollens reagent are referred to as reducing sugar. Eg. All monosaccharides like Lactose, Maltose are reducing sugar (1). 8. (a) Freon 12: It is used as aerosol propellants, refrigeration and air conditioner purposes. (b) DDT: It is used as insecticide. (1) 9. (a) It crystallizes in a cubic closed packed structure. Therefore, length of the side of the cube= 2√2r =2√2 x 1.25 x 10-8 cm =3.53 x 10-8 cm =353.6 pm. (1) (b) Volume of the unit cell = (3.53 x 10-8) 3 = 4.398 x 10-23 cm3 Therefore, number of unit cells present in 1 cm3 of Al =1/4.398 x 1023 = 2.27 x 1022 unit cell.(1) 10. (a) Aromatic amines are less basic than alphatic amines because in the former, lone pair of nitrogen is involved in the conjugation due to resonance. Thus, the availability of lone pair of donation decreases and acts as weak base. (1) www.cpprashanthschemistry.com Page 7 (b) Aniline reacts withAlCl 3 a lewis acid to form salt. Hence, it does not undergo Fridel Crafts alkylation (1). 11. (a) Potassium trioxalatoferate (III)(1) (b) Hexaamine platinum (IV) chloride.(1) 12.Correct structures (1/2 +1/2). OR S + O2→ S O2 S O2+ O2→ S O3 S O3 + H2SO4 →H2 S 2O7 H2 S 2O7 + H2O→ H2SO4 13. The slowest step of the reaction is: NO2 + NO2 → NO + NO3 (1) Hence, the rate of reaction is: Rate= K [NO2] [NO2] = K [NO2]2 (1) 14. (a) Secondary Amine [(CH3)2NH] Secondary amine gives insoluble substance with benzene sulphonyl chloride which remains unaffected on addition of acid. Tertiary Amine [(CH3)3N Tertiary amine does not react with benzene sulphonyl chloride and remains insoluble in alkali and can be dissolved in acid. (b) Primary Amine(CH3NH2) Does not give dye test www.cpprashanthschemistry.com Aromatic Amine (C6H5NH2) Aromatic amines produces yellow coloured azodye when it is treated with benzene diazonium chloride.. Page 8 15. (a) The electrode potential of F2 is maximum, which is why it is the strongest oxidizing agent(1). (b) Explanation with resonating structures.(1) 16. Correct definitions 17. (a) (i) Strong electrolyte: Those electrolytes which dissociate completely into ions are called strong electrolytes. Eg. NaOH, HCl, NaCl etc.(1/2) (ii) Weak electrolyte: Those electrolytes which do not ionize completely in aqueous solution or in molten state are called weak electrolytes. Eg. H2CO3, CH3COOH, etc.(1/2) (b)Cu/Cu2+ (aq)║Mg2+ (aq)/Mg E0 Cell =-2.37-(+0.34)=-2.71V. (1) 18. log K2 /K1=Ea /2.303R [1/T1 -1/T2] Log2=Ea x10 /2.303x8.314x300 x310 (1/2) (1/2) Ea =0.3010 x2.302 x8.314x300x310/10 (1/2) =53598.6J mol-1 ( (1/2) 19. (a) Transquilizers: The chemical substances used to cure mental diseases are called transquilizers. They reduce anxiety and tension. Eg. Calmpose, veronal etc.(1) (b)Preservatives: Chemical substances which are added to food to improve itsshelf life, appearance, taste and food value are called preservatives. Eg. Sodium benzoate. C6H5COONa.(1) (c) Analgesics: Those drugs which relieve or decrease pain are termed as analgesics. Eg. Analgin, etc.(1) 20. (a)Fuel cell: Electrical cells which are designated to convert the energy from combustion of fuels such as H2, or CH4 directly into electrical energy are called fuel cell. In this cell, the hydrogen and oxygen are bubbled through a porous carbon electrode into concentrated aqueous NaOH(1) At anode: 2H2(g)+ 4OH- (aq)→ 4H2O(l) +4e At cathode: O2(g) + 2H2O(l) +4e →4OH_(aq) www.cpprashanthschemistry.com Page 9 Overallreaction:O2(g) +2H2(g)→2H2O(l) (b)Fe2+ (aq) +Ag+((aq)→Fe3+(aq) +Ag(s) E0Ag/Ag =0.80v, E0Fe/Fe=0.77v. E0cell=E0Cathode-E0Anode =0.80-0.77=0.03V (1) G0= -nFE =2x96500x0.03=5790J/mol =5.790Kj/m0l(1). 21. Phenol to Acetophenone ( a )C6H5-OH + ( CH3CO)2O→C6H5( OCOCH3)+AlCl3→C6H4(OH) (OCOCH3)+Zn Distill→C6H5(COCH3)(1) (b)C2H5OH+[O]→CH3CHO+CH3MgBr/H2O→ (CH3)2CHOH (1) (a) C6H5NH2+diasotisation→C6H5N2Cl+boiling water→C6H5OH (1) 22. Calcination involves heating when volatile matter escapes leaving behind the metal oxide. Eg: ZnCO3 (s) → ZnO(s)+CO2(g) (1) Roasting the ore is heating it in presence of regular supply of air at high temperature below its melting point. Eg: 2PbS+3O2 → 2PbO +2SO2 (1) (b) To remove the iron oxide as iron silicate FeO +SiO2 → FeSiO3 (1) 23. Structure (I)undergo SN2 reaction (1) (b) Structure (I) UndergoSN2reaction because it is primary halide (1) (c) Structure (I) undergo SN2reaction faster because it is secondary halide and structure (II)is tertiary halide(1) 24. (a)It is based on the principle that the ions pass through the parchment membrane fsster in the electric field .(1) www.cpprashanthschemistry.com Page 10 (b)NH3 will be absorbed more readily because it has higher critical temperature. (1) (c)Multimolecular colloids consists of aggregation of small molecules or atoms.eg;sulphur sol. Macromolecular colloids consists of macromlecules ie polymers; eg starchsol.. 25. Two differences (2) One example each (1). OR i) vinyl chloride ii) tetra fluoro ethene (iii) caprolactum 26. (a)X-X’ bond present in inter halogen compounds is weaker than the X-X bonds present in halogens. (1) (b) d-orbital is present in phosphorous while it absent in nitrogen(1) (c)Because of large size and low ionization enthalpy.(1). 27. i) Vitamin B12 (ii) Yeast, milk (iii) Concern and love for her mother 28. (a) (i) Due to d-d transition.(1) (ii) Because the energy of(n-1)d orbital and ns orbitals are of coparable energy. (iii) Because of small size of their atoms other small atoms can be easily trapped in the interstitial space.(1) (b) 2KMnO4+5C2H2O4+3H2SO4→K2SO4+2MnSO4+10CO2 +8H2O (1) Or ionic equation 2KMnO4 +5SO2 +2H2O→K2SO4 +2MnSO4 +2H2SO4 (1) OR a) Are held by strong inter atomic forces. Explain. b) Ce(IV) is quite stable due to 4f0 configuration. Explain. c) Mn2+ has 3d5 configuration explain. www.cpprashanthschemistry.com Page 11 d) Cu(1) is not stable due to its less negative enthalpy of hydration than Cu(II). e) Due to lanthanoid contraction, the increase in radii of second to third transition series almost vanishes. 29. (a) (i)due to resonance stabilization of of benzoic acid meta position becomes electron rich.(1) (ii)Strong hydrogen bonding in benzoic acid.(1) (b)(i)CH3COCH3+[H]/Ni→CH3CH(OH)CH3+Con.H2SO4→CH3CH=CH2(1) (ii)C6H5COOH+SOCl2→C6H5COCl +H2 /PdBaSO4 →C6H5CHO (1) (iii)2CH3CH2OH +Mild oxidation (KMnO4 )→2CH3OH +NaOH→CH3CH3 (OH)CH2CHO (1) OR a) i) Aldol condensation; give the equation. ii) Acetone is treated with methyl magnesium bromide followed by hydrolysis. Equation. b) Mechanism c) i) The reaction of aceyl halide with acides, amines etc. give equation. ii) Reduction of acid halide with Pd and BaSO4 to form aldehyde. 30. Vant Hoff’s factor-correct definition and equation (1+1) ╖=ICRT (1) 0.70=ix0.0i03 x0.082 x (27+273) (1) I=0.70/0.0103 x0.082x300=2.76 (1) OR W2= 0.5g M2= 65amu W1= 100X1.58=158g P01-P1 W2 M1 www.cpprashanthschemistry.com Page 12 ----- = -----P01 M2 W1 0.5X154 P1= 143 - -------- X 143 65X158 =142 mm of Hg. b) Henry’s law m=KHP Application: i) bends, (ii) anoxia SAMPLE PAPER -10 Blue Print www.cpprashanthschemistry.com Page 13 Unit No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Unit VSA(1) The Solid State Solutions Electrochemistry Chemical Kinetics Surface Chemistry General Principles & Processes of isolation of elements p - Block Elements d & f elements Co - ordination Compounds Haloalkanes & Haloarenes Alcohols, Phenols & ethers Aldehydes, Ketones & Carboxylic acids Amines Biomolecules Polymers Chemistry in everday life SA(3) LA(5) 2 1 1 1 1 1 2 2 1 1 1 1 1 1 1 1 1 1 1 1 1 2 1 8 www.cpprashanthschemistry.com SA(2) 1 10 1 1 9 3 Page 14 Total 70 4 5 5 5 4 3 8 5 3 4 4 6 4 4 3 3 70