CLASS 11 CHEMISTRY EM MARCH 2018 TYPE A AND TYPE B ENGLISH MEDIUM ANSWER KEY DOWNLOAD- p.chakaravarthi M.SC, shepherds MATRIC HR SEC SCHOOL madapalli.

CLASS 11 CHEMISTRY EM MARCH 2018 TYPE A AND TYPE B ENGLISH MEDIUM ANSWER KEY DOWNLOAD- p.chakaravarthi M.SC, shepherds MATRIC HR SEC SCHOOL madapalli.

11th CHEMISTRY – Public exam -2018 - Type A - Answers Full SECTION I SECTION II 16. What is gravity separation? In gravity separation process the powdered ore is placed on a sloping floor and washed by directing on it a strong current of water. The lighter sandy and earthy impurities are washed away, while the heavier ore particles are left behind. 17. Write any two uses of D2O. (i) Used as moderator in nuclear reactor to slow down the speed of fast moving neutrons (ii) Used for the preparation of Deuterium . 18. In flame test Barium gives apple green color. Give reason. In flame test the electrons get energy and excite to higher energy levels, when they return to the ground state they emit the absorbed energy in the form of radiations having particular wave length. 19. What is meant by hybridization? Dissimilar orbitals with nearly the same energy on the same atom may combine or mix completely to form an equal number of equivalent energy new orbitals. The new orbitals of equal energy are called hybrid orbitals and the process is called hybridization. Qn No Option Answer 1 a 2 – 4 – 1 - 3 2 b Statement I & II are correct and statement II is the correct explanation of Statement I 3 b Olefins 4 a 0.5 5 a Kjeldhal’s method 6 b NH3 7 b rate 8 b O 2- , F9 d The halogen 10 b 1/16 11 a NO2 + 12 b Potassium sulphate 13 d Face centered cubic lattice 14 b I and II 15 d Both a and c www.kalvisolai.com 20. State first law of thermodynamics. First law of Thermodynamics: “Energy can be converted from one form to another, but cannot be created or be destroyed” 21. Reason out why equilibrium concentrations remain constant. At equilibrium the forward reaction and the reverse reactions take place endlessly and simultaneously with equal rates. They are in a state of dynamic equilibrium. So the equilibrium concentrations remain constant. 22. How will you identify ethane and ethylene with alkaline KMnO4 solution? Ethylene decolorizes alkaline KMnO4 whereas ethane doesn’t. Ethylene is converted into ethylene glycol by the action of cold dilute alkaline KMnO4 23. Benzene has equivalent six carbon atoms and six hydrogen atoms-justify. Benzene forms single mono substituted product and three di-substituted product . This justifies the fact that benzene has equivalent six carbon atoms and six hydrogen atoms. 24. How is benzyl chloride obtained from toluene? Benzyl chloride is obtained by chlorination of boiling toluene in light. C6H5-CH3 + Cl2 → C6H5-CH2Cl + HCl SECTION III 25. What is the simplest formula of the compound which has the following percentage composition? Carbon 80% Hydrogen 20%. Element % Rel.no of moles Simple ratio moles Simple whole number ratio C 80 80/12 = 20/3 (20/3)/(20/3) = 1 1 H 20 20/1=20 20/(20/3) = 3 3 The simplest formula is CH3 26. Explain calcination with an example. The method of conversion of ore into metal oxide is called calcination. In this process the ore is subjected to the action of heat at high temperature in the absence of air below its melting point. It is suitable for carbonate an hydrated ore. Calcination usually done in reverberatory furnace. Eg. CaCO3 (limestone) → CaO + CO2↑ www.kalvisolai.com 27. Arrange the order of increasing atomic volume (a) Li, Na, K (b) C,N,O (c) Ca,Sr, Ba (a) Li < Na < K because atomic radius increases down the group. Hence the volume. ( b) N < O < C generally atomic radius decreases along the period, but N has extra stability due to half-filled p orbital. Hence radius of N is less than that of O. ( c) Ca < Sr < Ba because atomic radius increase down the group. Hence the volume. 28. Draw (100) , (010), (001) planes. (100) (010) (001) 29. Write the significances of vanderwaal’s constants. ( i ) The term a/V2 is the measure of the attractive forces of the molecules. ( ii ) The vanderwaal constants ‘a’ and ‘b’ enable the calculation of critical constants of a gas. ( iii ) The inversion temperature of a gas can be expressed in terms of ‘a’ and ‘b’. Ti = 2a/Rb 30. Explain the geometry of SO2. In SO2 molecule there are three electron pairs on the S atom. The overall arrangement is trigonal planar. However, because one of the three electron pairs is a lone pair, the SO2 molecule has a ‘bent’shape and due to the lp-bp repulsive interaction the bond angle is reduced to 119.5 deg from the value of 120 deg. 31. Explain the fractional distillation method of purification. The process of separation of the components in a liquid mixture at their respective boiling points in the form of vapours and the subsequent condensation of those vapours is called fractional distillation. This is similar to ordinary distillation method but with the introduction of a fractionating column in between the distillation flask and the condenser. The fractionating columns are of different shapes. This method is suitable for the separation and purification of a mixture of two or more miscible liquids whose boiling points lie very close to each other. www.kalvisolai.com 32. What is the action of ozone on acetylene? Acetylene reacts with ozone and gives glyoxal and formic acid. O CHO CH ≡ CH + O3 → HC CH → + H2O2 → 2 HCOOH CHO O O (glyoxal) (formic acid) 33. How is benzene prepared commercially? Fractional distillation of petroleum gives naptha. This naphtha is passed over platinum supported over alumina catalyst gives benzene and its homologues. Benzene is separated from the mixture by solvent extraction and purified by fractional distillation. SECTION IV 34. What are the postulates of Bohr theory of atoms? Postulates of Bohr’s model of an atom: (i) The electrons revolve round the nucleus only in certain selected circular paths called orbits. These orbits are designated as K,L,M,N.. and numbered as 1,2,3,4…etc starting from the nucleus. Each orbit associated with definite energies called energy levels. (ii) As long as an electron remains in a particular orbit, it doesn’t loose or gain energy. Therefore these orbits are called stationary states. (iii) Angular momentum of electrons in an atom is quantized. mvr = nh/2π . It means those orbits are permitted in which angular momentum of the electron is a whole number multiple of h/2π (iv) If an electron jumps from one orbit to another, it will absorb or emit radiation of a definite frequency giving a spectral line of that frequency . (OR) What are ortho and para hydrogen ? explain When two hydrogen atoms combine they form molecular hydrogen. Depending upon the direction of the two proton in the nucleus , ortho and para hydrogen molecules are known. When the protons in the nucleii of both H-atoms spin in the same direction it is called ortho-hydrogen. When the protons in the nuclei of both H-atoms spin in opposite direction, it is called para -hydrogen.At room temperature ortho form is more stable than para form. At 25 K , the equilibrium shifted to para form. www.kalvisolai.com 35. Give one example to show Boron acts as a powerful reducing agent. Boron replaces Carbon from CO2. 3CO2 + 4B → 2 B2O3 + 3C How is Boron isolated from Borax.? Preparation of boron trioxide: Borax is treate with hot conc HCl acid when the sparingly soluble boric acid separates out. Na2B4O7 + 2HCl → 2 NaCl + H2B4O7 H2B4O7 + 5 H2O → 4H3BO3 Boric acid is strongly heated to form boron tri oxide. H3BO3 → B2O3 + 3H2O Reduction of Boron tri oxide to Boron: When Boron trioxide is heated to bright red with magnesium, Boron is obtained. B2O3 + 3Mg → 3MgO + 2B (OR) How is osmatic pressure determined by Berkley – Hartley method and also mention its advantages. Determination of osmotic pressure by Berkley-Hartley method The apparatus consists of two concentric tubes. The inner tube is made of semipermeable membrane with two side tubes. The outer tube is made of gun metal which contains the solution. The solvent is taken in the inner tube. As a result of osmosis, there is fall of level in the capillary indicator attached to the inner tube. The external pressure is applied by means of a piston attached to the outer tube so that the level in the capillary indicator remains stationary at . This pressure is equal to the osmotic pressure (p) and the solvent flow from inner to outer tube is also stopped. www.kalvisolai.com Advantages of this Method 1. The osmotic pressure is recorded directly and the method is quick. 2. There is no change in the concentration of the solution during the measurement of osmotic pressure. 3. The osmotic pressure is balanced by the external pressure and there is minimum strain on the semipermeable membrane. 36. Derive the relationship between ∆U and ∆H. By definition , H = U + PV When the system at constant pressure undergoes changes from an initial state with H1, U1, V1, P parameters to a final state with H2, U2, V2, P parameters, then the change in enthalpy ∆H is given by ∆H = (H2 - H1) = (U2 - U1) + P(V2 - V1) i.e ∆H = ∆U + P∆V. -------------(1) We know that PV = nRT At constant temperature and pressure, P (V2 – V1) = (np – nr)RT or P∆V = ∆ng RT Substituting in (1) ∆H = ∆U + ∆ng RT ( ∆ng refers to the difference in number of moles of product to reactant gases.) (OR) Two moles of H2 and three moles of I2 are taken in 2 dm3 vessel and heated. If the equilibrium mixture contains 0.8 moles of HI , calculate Kp and Kc for the reaction H2 + I2 2HI Kc for the formation of HI equilibrium reaction is given by Kc = [( )( )] Given 2x = 0.8 , therefore x = 0.4 and 4x2 = 0.64 a = 2 , therefore (a-x) = 1.6 b = 3 , therefore (b-x) = 2.6 Substituting in Kc equation above, Kc = = 2/13 = 0.1538 Since ∆n = 0, Kp = Kc = 0.1538 (Answer) www.kalvisolai.com 37. Generally photochemical reactions follow zero order kinetics. How? The reaction in which the reaction rate is not affected by the concentration of reactants is called as zero order reaction, In photo chemical reactions, with increase in the intensity of the light (or) radiation, the product yield increases. For photosynthesis light radiation is essential and the process does not proceed in the absence of light. Here the rate of the reaction depends on the intensity of light radiation and not on the concentration of reactants. Hence the order is zero. Write any three differences between order and molecularity of the reaction. Differences between the concepts of order and molecularity Order of a reaction Molecularity of a reaction 1. It is the sum of powers raised on concentration terms in the rate expression. 1. It is the number of molecules of reactants taking part in elementary step of a reaction. 2. Order of a reaction can be zero, fractional or integer. 2. Molecularity can neither be zero nor fractional. 3. It depends upon pressure, temperature and concentration (for pseudo order) 3. It is independent of pressure and temperature (OR) Write the characteristics of homologous series. Characteristics of homologous series (1) All members of a series contain same elements and the same functional groups. (2) All the members of a homologous series can be represented by a general formula (3) All the members of a homologous series can be prepared by similar methods. (4) All members of a homologous series usually undergo similar chemical reactions. (5) Successive members in a series differ by a -CH2 group (6) The physical properties of the members of a homologous series vary in a regular way. Identify the homologous series having the general formula CnH2n and CnH2n-2 CnH2n are Alkenes CnH2n-2 are Alkynes www.kalvisolai.com 38. How will you estimate oxygen? Estimation of oxygen Oxygen is commonly estimated by the method of difference. The percentage of all other elements are added together and then subtracted from 100. The balance is the percentage of oxygen. Explain about carius method of estimation of sulphur. Estimation of sulphur by Carius method A known mass of the organic compound is heated in a sealed tube with fuming nitric acid. The sulphur present in the organic compound will be oxidised to sulphuric acid. The tube is cooled and broken in dilute hydrochloric acid. Then excess of barium chloride solution is added. The precipitate of barium sulphate obtained is filtered, washed, dried and weighed accurately. 1. Organic compound 2. Nitric acid 3. Iron tube 4. Carius tube Calculations Mass of the organic compound = w g Mass of barium sulphate = w1 g 233.4 g BaSO4 contains 32 g sulphur Therefore, w1 g BaSO4 will contain w1 x g sulphur Percentage of sulphur = x x 100 (OR) Explain the mechanism involved in hydrolysis of tert. Butyl bromide. The mechanism involved in hydrolysis of tert.butyl bromide is SN1 , substitution nucleophilic unimolecular. The reaction consists of two steps. Step 1: The alkyl halide ionises to give the carbocation. This step is the slow rate determining step. Tert.butylbromide carbocation The carbocation is planar because the central positively charged carbon atom is sp2 hybridised. Step 2 : The nucleophile can attack the planar carbocation from either side to give tertiary butyl alcohol. Prepared