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CBSE Class 11 Pre Board 2019 : Chemistry (St Xavier's Sr. Sec. School, Delhi)

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Annual Examination in CHEMISTRY Std. 11 16-2-2019 Time : 3 hrs. Max. Marks : 70 General Instructions: i) Question numbers 1 - 5 carry 1 mark each. ii) Question numbers 6 - 12 carry 2 marks each. iii) Question numbers 13 - 24 carry 3 marks each. iv) Question numbers 25 - 27 carry 5 marks each. v) Use log table if necessary. 1. What is common ion effect? (OR) What are Lewis bases? Give an example. (1) 2. Boiling point of alkanes increases down the homologous series. Explain. (1) 3. B3+ ions are not known. Why? (1) 4. Write the IUPAC name of the product obtained by the addition reaction of HBr to Hex-1-ene in the presence of a peroxide. (1) 5. Differentiate between oxidation number and valency. (1) 6. a) b) Butan-2-one and Butanal are isomers. Name the type of isomerism. Why addition reaction of alkenes are electrophilic in nature? (OR) What are Grignard reagents? Give chemical equation for the preparation of propane from a Grignard reagent. (2) 7. a) b) Give an example for homogeneous equilibria. State Le-Chatlier s Principle. (2) 8. a) b) Why does aluminium chloride behave as Lewis acid? What happens when orthoboric acid is heated? (2) 9. a) Write the IUPAC name: i) CH3 - CH - CH2 - CH - CH3 OH ii) CH3 OCH3 b) 10. (OR) Draw the structure of the following: i) 2-Methyl pent-1, 4-diene ii) 3-Chloro 4-ketohexanal (2) Complete the following reactions: a) b) Std. 11 COOH NaNO3 Li +O2 Heat (2) -2- CHEMISTRY 11. Calculate the solubility of BaSO4 if its Ksp value is 1.1 x 10-10. (2) 12. Account for the following: i) PbX2 is more stable than PbX4 ii) Atomic radius of gallium is less than that of aluminium. (2) Explain the following with a chemical equation: i) Decarboxylation ii) Friedel crafts acylation iii) Wurtz Reaction (3) Commercially available concentrated hydrochloric acid contains 38% of HCl by mass and has a density of 1.19g/cm3. Calculate the molarity of this concentrated hydrochloric acid. (Molar Mass of HCl = 36.5g mol 1) (3) 13. 14. 15. 16. 17. 18. 19. a) b) 21. Std. 11 (3) a) Distinguish between intermolecular and intramolecular hydrogen bonds giving suitable example. b) What are sigma bonds? Why sigma bonds are stronger than pi bonds? (OR) Define hybridization. With the help of hybridization, explain the shape of ammonia molecule. (3) (Atomic No. of N = 7, H = 1) Draw a neat labelled diagram for the galvanic cell which represents the following chemical reaction: Zn (s) + CuSO4(aq) ZnSO4(aq) + Cu(s) Also explain how is the electrical neutrality maintained in the solution of two half cells? (3) a) b) Define molality. Why is it preferred over molarity? If 4g of NaOH dissolves in 36g of water, calculate the mole fraction of each component in the solution. (Atomic Mass of H = 1u, Na = 23u, O = 16u) (3) a) Balance the following reaction in acidic medium: Fe2+ + Cr2O72- + H+ Fe3+ + Cr3+ What is meant by electrochemical series? (3) b) 20. Discuss the stability of carbocations on the basis of inductive effect. 0.3780g of an organic chloro compound gave 0.5740g of AgCl in carius estimation. Calculate the percentage of chlorine in the compound. (Atomic Mass of Cl = 35.5u, Ag = 108u) Write the mechanism of nitration of benzene. (OR) Addition of HBr to propene gives 2-Bromopropane as the major product. Explain giving mechanism. (3) An electrochemical cell is set up between two half cells Al3+/Al and Mg2+/Mg. The reduction potentials of these half cells are -1.66V and -2.36V respectively. a) Write the half cell reactions. b) What will be the overall reaction? c) Name the positive electrode. d) Calculate the EMF of the cell. (OR) -3- CHEMISTRY 22. 23. 24. 25. a) Given the standard electrode potential: K+/K= -2.93V, Ag+/Ag = +0.80V, Cr3+/Cr= -0.74V. Out of these electrodes which will be the strongest reducing agent? b) Can a solution of 1M CuSO4 be stored in a vessel made of Nickel metal? Given that E Ni/Ni2+ = +0.25V, E Cu/Cu2+ = -0.34V. a) What is meant by entropy? Why is entropy of a substance taken as zero at zero Kelvin? b) Calculate the enthalpy change for the reaction: H2(g) + Br2(g) 2HBr(g). Given that the bond enthalpies of H-H, Br-Br and H-Br are 435, 192 and 364 kJ/mol respectively. (3) Account for the following: a) Beryllium and Magnesium do not give flame colouration. b) Alkali metals are not found in nature. c) Solution of alkali metals in liquid ammonia is coloured. (OR) a) Name the following: i) Alkali metal which shows diagonal relation with magnesium. ii) A metal which forms superoxide. b) Define hydration enthalpy. How is it related to atomic size? c) List two properties of lithium in which it differs from rest of the family members. (3) Explain the following: a) In PCl5, axial bonds are longer than equatorial bonds. b) Each carbon oxygen bond in CO2 molecule is polar, but the molecule itself is non-polar. c) HF has higher boiling point than HCl. a) Carry i) ii) iii) b) OH group in phenol is ortho-para directing and activating. Explain with the help of resonance structures. (OR) Arrange the following in the decreasing order of reactivity towards electrophilic substitution reaction. Nitrobenzene, Toluene, Benzene a) (3) out the following conversions: Phenol to Chlorobenzene Benzene to p-nitrobromobenzene Ethyne to but-2-yne b) Give a chemical test to distinguish between: i) ethane and ethene ii) But-1-yne and But-2-yne c) Complete the following reaction: Na / ether A (CH3)3 C - Br d) Std. 11 (3) Alc. KOH B An alkene A on ozonolysis gives a mixture of ethanal and pentan-3-one. Write the structure and IUPAC name of A. -4- (5) CHEMISTRY 26. a) State any two characteristics of equilibrium constant. b) Calculate the pH of 0.02M NaOH solution. c) Two moles of PCl5 were heated to 600K in closed two litre vessel. When equilibrium was attained, PCl5 was found to be 40% dissociated into PCl3 and Cl2. Calculate the Kc and Kp for this reaction. (R = 0.0821 lit atm/K/mol) (OR) 27. a) Chemical equilibrium is dynamic in nature. Explain. b) Calculate the degree of ionization and hydronium ion concentration of 0.01M solution of HCN. Ka = 4.8 x 10-10 c) Two moles of PCl5 were heated to 600K in closed two litre vessel. When equilibrium was attained, PCl5 was found to be 40% dissociated into PCl3 and Cl2. Calculate the Kc and Kp for this reaction. (R = 0.0821 lit atm/K/mol) a) Calculate the standard heat of formation of ammonia if its heat of reaction is - 46.2 KJ mol-1 b) Calculate the enthalpy change accompanying the transformation of C(graphite) to C(diamond). Given that enthalpies of combustion of graphite and diamond are 393.5 and 395.4 KJ/mol respectively. c) For the reaction, Ag2O(s) 2Ag(s) + O2(g), H = 30.56KJ/mol and S = 0.066KJ/mol. Calculate the temperature at which G equals to zero. (OR) State First law of thermodynamics. a) b) Predict the sign of S for the following reactions: i) H2(g) 2H(g) ii) 2SO2(g) + O2(g) 2SO3(g) c) Calculate the standard Enthalpy of formation of CH3OH from the following data: CH3OH (l) + 3/2 O2(g) H2(g) + O2 (g) C(g) + O2(g) CO2 + 2H2O(l) H2O(l) CO2(g) (5) H = -726 KJ/Mol H = -286 KJ/Mol H = -393 KJ/Mol (5) -x-x-x-x-x-x-x-

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