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BISHOP COTTON GIRLS SCHOOL I TERM EXAMINATION JANUARY 2021 CHEMISTRY STD XI 21-1-2021 Max Marks : 70 Reading time:9 AM to 9.10 AM Writing time: 9.10 AM to 12.10 PM Instructions: Your Log in time is 8.45 AM and Uploading time is 12.10 to 12.30 PM. Students are required to read, complete the paper and upload the clear copies of the answer scripts with your name as the pdf file name in the given time on assignment itself as informed earlier. Question 1 is of 20 marks having four sub parts, all of which are compulsory. Question numbers 2 to 8 carry 2 marks each with any two questions having internal choice. Question numbers 9 to 15 carry 3 marks each with any two questions having an internal choice. Question numbers 16 to 18 carry 5 marks each with an internal choice . All working including rough work should be done on the same sheet as, and adjacent to the rest of the answer. Balanced equations must be given wherever possible ,and diagrams where they are helpful. When solving numerical problems , all the essential working must be shown. The intended marks for questions or part of questions are given in brackets [ ]. ---------------------------------------------------------------------------------------------------------------------------------------QUESTION-1. (a) Fill in the blanks with appropriate words: [4x1=4] i. Ammonium chloride solution is ---------- because of ----------hydrolysis. ii. According to the Law of Mass Action , the rate of chemical reaction is ----------proportional to the product of the -----------------of reactants. iii. In conversion of Cl 2 to ClO3 -- the oxidation state of Chlorine changes from ------ to ------. iv. The chlorides of Beryllium and Aluminium are soluble in ----------- solvents and behave as strong Lewis -------------. (b) Select the correct alternative from the choices given: [4x1=4] i. The correct set of four quantum numbers for the valence electron of Rubidium (Z=37) is: 1. 5,0,1, +1/2 2. 5,1,0, +1/2 3. 5,0,0 +1/2 4. 5,1,1, +1/2 ii. Which of the following molecules contain no pi bonds? iii. iv. (c) (d) 1. CO2 2. H2O 3. SO2 4. NO2 In the reaction 2 FeSO4 + H2SO4 +H2O2 Fe 2(SO4)3 + 2H2O, the oxidizing agent is/are: 1. Both H2SO4 and H2O2 2. H2O2 3. FeSO4 4. H2SO4 Which of the following alkyl groups has the highest inductive effect? 1. (CH3) 3C 2. (CH3 ) 2C H 3. CH3CH2 4. C H3 Match the following: [4x1=4] 1. Azimuthal quantum number a. Specific rotation 2. Alums b. Sodium Hydroxide 3. Polarimeter c. Number of shells 4. Castner Kellner shell d. Antiseptic Answer the following questions: [2x4=8] i. BF3 is non-polar while NF3 is polar. Give reason. ii. Dissociation of H2 S is suppressed in acidic medium. Explain iii. What will be the percentage dissociation in 0.1 M CH3COOH at equilibrium having dissociation constant 1.8x10-5. iv. Draw the isomers of a compound with molecular formula C 3H9N. Name these isomers and their type of isomerism. QUESTION-2 [2] a. On complete combustion 0.246 gm of an organic compound gave 0.198 gm of CO 2 and 0.1014 gm of water . Determine the percentage of carbon and Hydrogen in the compound. [C=12, O=16, H=1] OR In a Carius method for estimation of Phosphorous 0.31 gm of an organic compound gives 0.55 gm of Mg2P2O2 . Calculate the percentage of Phosphorous in the organic compound. [Atomic weight of Mg=24, P=31, O=16] QUESTION-3 [2] Complete and balance the following equation: i. ii. PbS + H2O2 ------------- + ----------------H2O2 + Cl 2 -------------- + ---------------- QUESTION-4 [2] Consider the following reversible reaction N2O4 + 2NO2(g) . How is the composition of the equilibrium mixture affected by : (1).A change in temperature (2). A change in pressure ( 3). A change in concentration of N2O4 (4). The removal of NO2 from the reaction mixture. QUESTION-5 [2] Write the IUPAC names of the following compounds: i. CH3 CH CH2 CH CH2- NH2 ii. CH C - CH CH CH2 CONH2 I I I I COCH3 OH Cl OH QUESTION-6 [2] Define Ionisation enthalpy. Why is the first ionization enthalpy of Beryllium greater than that of both Lithium and Boron QUESTION-7 [2] What do you understand by S N1 mechanism . Explain by using a suitable example. OR Draw the structures of all the isomers of Tartaric acid. Which amongst these is optically inactive? QUESTION-8 [2] Explain why: 1. Beryllium and magnesium do not give colour to the flame unlike other group 2 elements. 2. Lithium fluoride is almost insoluble in water whereas Lithium chloride is soluble in water but also in acetone. QUESTION-9 i. ii. [3] What is the number of unpaired electron in Cr 3+ ? (Atomic number=24) Calculate the energy in joules required to shift the electron of the hydrogen atom from the first Bohr orbit to the fifth Bohr orbit and what is the wavelength of the light emitted when the electron returns to the ground state. The ground state electron energy is 2.18x10-11 ergs. QUESTION 10 a. Draw the molecular orbital diagram of N 2 molecule. State the bond order, stability of the molecule and the magnetic behaviour of nitrogen molecule. [3] OR b. Explain the hybridization in PCl 5 molecule .Why are axial bonds longer than the equatorial bond? QUESTION-11 [3] Give balanced chemical equations for the following reactions: i. ii. iii. Sodium sulphite is boiled with sulphur. Sodium thiosulphate is reacted with Iodine Ammonium chloride is heated with calcium hydroxide QUESTION-12 [3] a. Discuss the shapes of the following molecules using VSEPR theory. 1. H2O 2. NH3 3. CH4 OR b. Define Hydrogen bonding . Explain the different types of Hydrogen bonding with an example for each type. QUESTION-13 [3] Draw the Isomers of the following compounds and state the type of Isomerism exhibited by these compounds. 1. Azobenzene 2. Lactic acid 3. Acetophenone QUESTION-14 [3] a. Draw the resonating structures of C 6H5NO2. b. Give two points of differences between Inductive effect and Mesomeric effect. QUESTION-15 [3] a. Arrange the following species in decreasing order of their relative stability . 1. O2 , O2+ , O2 - , O222. N2 , N2+ , N2 -, N2 2b. State the type of hybridization associated with sulphur in SF 6 . QUESTION-16 a. i. Give the mathematical form of Henderson equation for acidic and basic buffer. [5] ii.0.15 mole of Pyridinium chloride has been added to 500 Cm 3 of 0.2 M Pyridine solution. Calculate the PH and hydroxyl concentration in the resulting solution assuming no change in volume. (Kb for pyridine =1.5x10-9 ). OR b. i. What is the effect of temperature on ionic product of water? How will it change the P H values of a neutral solution. ii.The ionization constant of nitrous acid is 4.5x10-4 . Calculate the P H of the 0.04 M Sodium nitrite solution and also its degree of dissociation. QUESTION-17 [5] a. i. Balance the following equations using the methods specified in the brackets: 1. Cr2 O7 2- + Fe 2+ + H + Cr3+ + Fe 3+ + H2 O ( ion electron method) 2. Cu + HNO3 Cu(NO3) 2 + NO + H2 O ( oxidation number method) ii.Find the oxidation number of the following: 1. S in S2 O322. Cl in HClO4 OR b. Give reasons for the following statements: i. 1. Boron is unable to form BF63- ion but aluminium forms AlF63- ion. 2.Boric acid is considered as a weak acid. 3.Silicon shows a higher covalency than carbon. ii. Write balanced equations: 1. Preparation of Boric acid from Borax. 2. Aluminium reacts with aqueous NaOH. QUESTION-18 [5] a. i. State Le-Chatliers Principle ii.Using Le-Chatliers principle explain the effect of pressure on solubility of gases in liquids. iii.A sample of HI (g) is placed in flask at a pressure of 0.2 atm. At equilibrium the partial pressure of HI (g) is 0.04 atm. What is the KP for the given equilibrium. OR b. i.State Ostwald s dilution law. Derive a mathematical expression for Ostwald s dilution law. ii.Give the conjugate acid and conjugate base for NH3. iii.The solubility product of barium sulphate is 1.5x10-9. Calculate its solubility in: 1. pure water 2. 0.1 M BaCl 2 . ************
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