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PRELIMINARY EXAMINATION 1 (2024-25) CHEMISTRY GRADE XII Maximum Marks: 70 Time Allotted: Three Hours Reading Time: Additional Fifteen minutes Instructions to Candidates You are allowed additional 15 minutes for only reading the question paper. You must NOT start writing during the reading time. This question paper has 7 printed pages. It is divided into four sections and has 21 questions in all. All questions are compulsory. Answer all questions. Section A has fourteen subparts. Each question carries 1 mark. While attempting Multiple Choice Questions in Section A, you are required to write only ONE option as the answer. Section B has ten questions. Each question carries 2 marks. Section C has seven questions. Each question carries 3 marks. Section D has three questions. Each question carries 5 marks. Internal choices have been provided in one question each in Sections B, C and D. The intended marks for questions are given in brackets [ ]. 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 essential workings must be shown. In working out problems, use the following data: Gas constant R=1 987cal deg-1mol-1=8 314JK-1mol-1 =0 0821dm3atmK-1mol-1, 1 l atm =1dm3atm=101 3 J. 1 Faraday=96500 coulombs. Avogadro s number= 6 023 1023. .. This paper contains 14 printed pages ISC SECTION A- 14 Marks Question1 (A) (i) (ii) (iii) (iv) (B) (i) (ii) (iii) (iv) (v) Fill in the blanks by choosing the appropriate word(s) from [4x1] those given in the brackets: (zero, ethylethanoate, first, octahedral, diethylether, dependent, ethene, anode, chloroform, independent, square planar, cathode, phosgene, tetrahedral, glucose) For a particular reaction, the value of rate constant is 0.05 s-1. The reaction is of ________ order and will be ______of initial concentration. The dehydration of ethyl alcohol with conc. H2SO4 at 140 C mainly yields _______ while at 170 C the mail product is ________. In a galvanic cell, the movement of electrons in the external circuit is from _______ to ________. The geometry of [Ni(CN)4]-2 and [NiCl4]-2 are ________ and _________ respectively. Select and write the correct alternative from the choices given [7x1] below: Which of the following gives the carbylamine test? (a) (C2H5)3N (b) (C2H5)2NH (c) C2H5NH2 (d) C2H5NHCH3 For a spontaneous reaction, G; Kc and Eocell will be respectively: (a) -ve, >1, +ve (b) +ve, >1, -ve (c) -ve, <1, -ve (d) -ve, >1, -ve The rate of a reaction between two reactants A and B decreases by a factor of 4 if the concentration of reactant B is doubled. The order of the reaction with respect to B is: (a) 2 (b) -1 (c) 1 (d) -2 CH3CHO and C6H5CH2CHO can be distinguished chemically by: (a) Benedict s test (b) Iodoform test (c) Tollens reagent test (d) Fehling s solution test In comparison to a 0.01M solution of glucose, the depression of freezing point of a 0.01M MgSO4 solution is: (a) The same 2 (vi) (vii) (b) About twice (c) About three times (d) About half Assertion: Ethanol is less acidic than water. Reason: The electron releasing inductive effect of the ethyl group decreases the acidic character. (a) Assertion and reason both are true and reason is correct explanation for assertion. (b) Assertion and reason both are true but reason is not correct explanation for assertion. (c) Assertion is true but reason is false. (d) Assertion is false but reason is true. Assertion: Conductivity of all electrolytes decreases on dilution. Reason: On dilution number of ions per unit volume decreases. (a) Assertion and reason both are true and reason is correct explanation for assertion. (b) Assertion and reason both are true but reason is not correct explanation for assertion. (c) Assertion is true but reason is false. (d) Assertion is false but reason is true. (C) Read the passage carefully and answer the questions that [3x1] follow. When an aldehyde with no a-hydrogen reacts with concentrated aqueous NaOH, half the aldehyde is converted to carboxylic acid salt and other half is converted to an alcohol. In other words, half of the reactant is oxidized and other half is reduced. This reaction is known as Cannizzaro reaction. (i) A mixture of benzaldehyde and formaldehyde on heating with aqueous NaOH solution gives: (a) benzyl alcohol and sodium formate (b) sodium benzoate and methyl alcohol (c) sodium benzoate and sodium formate (d) benzyl alcohol and methyl alcohol Which of the following compounds will undergo Cannizzaro reaction? (a) CH3CHO (b) CH3COCH3 (c) C6H5CHO (d) C6H5CH2CHO (ii) 3 (iii) Trichloroacetaldehyde is subjected to Cannizzaro s reaction by using NaOH. The mixture of the products contains sodium trichloroacetate ion and another compound. The other compounds is: (a) 2, 2, 2-trichloroethanol (b) trichloromethanol (c) 2, 2, 2-trichloropropanol (d) chloroform SECTION B 20 MARKS Question2 [2] Account for the following: a) Zr and Hf exhibit similar properties. b) The paramagnetic character in 3d transition series elements increases up to Mn and then decreases. Question3 [2] Two students X and Y were studying the basicity of compounds. X wrote that ammonia is less basic than methylamine whereas Y wrote that ammonia is more basic than methylamine. According to you, whose answer is correct? How have you concluded this? [2] Question4 Vitamins are required in very small amount for the healthy growth of organisms. When a person does not get a particular vitamin in diet, she/he may suffer from certain diseases. Normal functioning of an organism can be greatly affected due to deficiency of vitamins in the body. (a) Which vitamin deficiency causes rickets and scurvy? (b) Do you think, all vitamins are soluble in water? Explain by giving an example. Question5 [2] A solution of Al(NO3)3 is electrolysed between platinum electrodes using a current of 6 amperes for 50 minutes. What mass of aluminium is deposited at the cathode? [At. Mass of Al = 27]. Question6 [2] The osmotic pressure of blood at 37 C is 8.21 atm. How much glucose in grams should be used per litre of aqueous solution for an intravenous injection so that it is isotonic with blood? [Molecular weight of glucose = 180g/mol] Question7 [2] Starting with acetic acid, discuss the role of one F and one Cl groups play on the acidity of the acid when they replace a hydrogen atom of CH3 group of acetic acid. Answer by arranging the acids in increasing acid strength followed by explanation. 4 [2] Question8 John was making noodles in boiling water. When he added common salt to boiling water, the water stopped boiling for a short while. If john had added 15.0 g of NaCl to 250.0 g of water, calculate the boiling point of solution assuming NaCl dissociates completely in water.(Kb for water= 0.512 K kg/mol, molecular mass of NaCl=58.5 g/mol) Question9 (i) (ii) [2] Give one chemical test for each to distinguish between the following pair of compounds: (i) Acetaldehyde and Benzaldehyde (ii) Acetic acid and Benzoic acid OR How will you prepare the following compounds? (a) Butan-2-one from propanoic acid. (b) m-chlorotoluene from benzaldehyde. Question10 [2] Give balanced equation for the following: (i) Formaldehyde is treated with ammonia. (ii) Mixture of calcium acetate and calcium formate is dry distilled. Question11 [2] Write down the formula of : (a)Tetraamineaquachloridocobalt(III) chloride (b) Triamminechloridonickel (II) nitrate SECTION C 21 MARKS Question12 [3] Give balanced equations for the following name reactions: (a) Rosenmund s reduction (b) Hoffmann Bromamide reaction (c) Aldol Condensation Question13 [3] Write down the IUPAC name of the following: a. [Co(NH3)4 (H2O)2]Cl3 b. K2[Ni(CN)4] c. [Pt(NH3)4Cl2][PtCl4] Question14 [3] Calculate the standard cell potentials of the galvanic cells in which the following reactions take place. Question15 (i) (ii) [3] [2] For the complex [Fe(en)2Cl2]Cl a) the oxidation number of iron b) the magnetic behaviour of the complex (b) On the basis of crystal field theory, write the electronic [1] configuration for d4 ion if 0 < P. 5 Question16 (i) (ii) (iii) (iv) The half-life for radioactive decay of 14C is 5730 years. An archaeological artifact containing wood had only 80% of the 14C found in a living tree. Estimate the age of the sample. For a reaction, A + B Products, the rate law is given by : r = k [A]1/2[B]2. What is the order of reaction? OR The rate of the chemical reaction doubles for an increase of 10 K in absolute temperature from 298 K. Calculate Ea. Time required to decompose SO2Cl2 to half of its initial amount is 60 minutes. If the decomposition is a first order reaction, calculate the rate constant of the reaction. Question17 [3] [2] [1] [2] [1] [3] How will you bring about the following conversions: a) Propanone to Propene b) Benzaldehyde to Benzophenone c) Benzene to p-nitrobenzaldehyde Question18 [3] An organic compound (A) (molecular formula C8H16O2) was hydrolysed with dilute sulphuric acid to give a carboxylic acid (B) and an alcohol (C). Oxidation of (C) with chromic acid also produced (B). On dehydration (C) gives but-1-ene. Write the equations for the reactions involved. SECTION D 15 MARKS Question19 (i) [5] (c) Read the given passage and answer the questions that follow: Alcohols play very important role in our daily life. Ordinary sprit used as an antiseptic contains methanol. Ethanol is present in cough syrups, tonics, wine, beer and whisky, Sugar, starch, cellulose is carbohydrates which also contain large number of - OH groups. Phenol is also an antiseptic in low concentration (0.2%) where as 2% solution of phenol is used as disinfectant. The fragrance of rose is due to citronellol (unsaturated alcohol). Phenol is used for preparation of many useful compounds like aspirin, methyl salicylate (Iodex) and phenyl salicylate (salol) used as intestinal antiseptic. How is phenol prepared from cumene? What is advantage of [2] this method? Convert phenol to picric acid. [1] (d) Distinguish between phenol and benzyl alcohol? [1] (e) Why does phenol turn pink after long standing? [1] (a) 6 Question20 (i) [5] A reaction is second order with respect to a reactant. How is the rate of reaction affected if the concentration of the reactant is: (i) Doubled (ii) Reduced to half? Question21 [5] (i) How many primary amines possible with this formula C4H11N? (ii) Give a chemical test to distinguish between ethylamine and [3] aniline. Write the reactions involved. Write the balanced equation for carbylamines reaction. [1] (iii) [1] OR (i) (ii) Electrophilic substitution in case of aromatic amines takes place [2] more readily than benzene. Account for it. Carry out the following conversions: [3] (a) Nitrobenzene to benzoic acid. (b) Benzyl chloride to 2-phenylethanamine (c) Aniline to benzyl alcohol ************************************ 7
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