Chemistry Class 11th Past Paper PDF

ANNUAL EXAMINATION CLASS – 11TH SUBJECT –CHEMISTRY TIME – 3 Hr FULL MARKS - 70 GENERAL INSTRUCTIONS:- I. There are 35 questions in this question paper...

ANNUAL EXAMINATION CLASS – 11TH SUBJECT –CHEMISTRY TIME – 3 Hr FULL MARKS - 70 GENERAL INSTRUCTIONS:- I. There are 35 questions in this question paper with internal choice. II. Section A consists of 19 multiple – choice questions carrying 1 mark each. III. Section B consists of 5 very short answer questions carrying 2 marks each. IV. Section C consists of 6 short answer questions carrying 3 marks each. V. Section D consists of 2 case based questions carrying 4 marks each. VI. Section E consists of 3 long answer questions carrying 5 marks each. VII. All questions are compulsory. VIII. Use of log tables and calculators is not allowed. (SECTION – A)  The following questions are multiple – choice questions with one correct answer. Each question carries 1 mark. There is no internal choice in this section. 1. Which one of the following pairs of gases contains the same number of molecules (a) 16 g of O2 and 14 g of N2 (b) 8 g of O2 and 22 g of CO2 (c) 28 g of N2 and 22 g of CO2 (d) 32 g of O2 and 32 g of N2 2. For N2  3H2 ⇌ 2NH3  heat (a) Kp =Kc (RT) (b) Kp =Kc (RT) (c) Kp =Kc (RT)-2 (d) Kp =Kc (RT)-1 3. In the reaction N2  3H2 2NH3 , the product increases on (a) Increasing temperature (b) Increasing pressure (c) Increasing temperature and pressure both (d) Decreasing temperature and pressure both (e) None of these 4. Conjugate base of H2PO4 is (a) PO4-3 (b) H2PO4- (c) H3PO4 (d) H4PO3 5. Which of the following is not Lewis acid (a) FeCl3 (b) AlCl3 (c) BCl3 (d) NH3 6. 7. 8. 9. Which of the following alkenes gives only acetic acid and on oxidation with potassium permanganate solution (a) Ethylene (b) 1-Butene (c) Propene (d) 2-Butene 10. The size of the following species increases in the order (a) Mg+2  Na+  F-  Al (b) F- < Al < Na+ < Mg+2 (c) Al  Mg+2  F-  Na+ (d) Na+ < Al < F- < Mg+2 11. The ionization energy of an element is (a) The same as the electron affinity of the element (b) Equal in magnitude but of opposite sign to the electron affinity of the element (c) The energy released when an electron is added to an atom of the element (d) The energy required to remove the outermost electron of an atom of the element 12. On-going from right to left in a period in the periodic table the electronegativity of the elements (a) Increases (b) Decreases (c) Remain unchanged (d) Decreases first then increases 13. 14. 15. Orbital is (a) Circular path around the nucleus in which the electron revolves (b) Space around the nucleus where the probability of finding the electron is maximum (c) Amplitude of electrons wav e (d) None of these  Read the assertion and reason carefully to mark the correct option out of the options giv en below : (a) If both assertion and reason are true and the reason is the correct explanation of the assertion. (b) If both assertion and reason are true but reason is not the correct explanation of the assertion. (c) If assertion is true but reason is false. (d) If the assertion and reason both are false. (e) If assertion is false but reason is true. 16. Assertion : The cation energy of an electron is largely determined by its principal quantum number. Reason : The principal quantum number n is a measure of the most probable distance of finding the electron around the nucleus. 17. Assertion : Atoms can neither be created nor destroyed. Reason : Under similar condition of temperature and pressure, equal volume of gases does not contain equal number of atoms. 18. Assertion : Catalyst affects the final state of the equilibrium. Reason : It enables the system to attain a new equilibrium state by complexing with the reagents. 19. Assertion: But-1-ene and 2-methylprop-1-ene are position isomers. Reason: Position isomers have same molecular formula but differ in position of functional group or C = C. (Section B) (very short answer type questions each carry 2 marks) 20. Calculate the average atomic mass of hydrogen using the following data :- Isotope % natural abundance Molar mass 1 H 99.985 1 2 H 0.015 2 21. How will you calculate work done on an ideal gas in a compression, when change in pressure is carried out in infinite steps? 22. How can you predict the following stages of a reaction by comparing the value of Kc and Qc? (i) Net reaction proceeds in the forward direction. (ii) Net reaction proceeds in the backward direction. (iii) No net reaction occurs. 23. Explain the following reactions:- (a) Wurtz reaction (b) Decarboxylation 24. What is the IUPAC name of the following compound?  (Section C) (Very short answer type questions each carry 3 marks) 25. Explain the following: (a) Electronegativity of the given elements increases as we move from left to right in the periodic table. (b) Ionisation enthalpy decreases in a group from top to bottom? OR What is the basic difference in the required approach between Mendeleev’s Periodic Law and the Modern Periodic Law? 26. OR Calculate the pH of a solution formed by mixing equal volumes of two solutions A and B of a strong acid having pH = 6 and pH = 4 respectively. 27. Match column 1 with column 2 for the oxidation states of the central atoms. Column 1 Column 2 -2 A. Cr2O7 1. +3 B. MnO4- 2. +4 - C. VO3 3. +5 D. FeF63- 4. +6 5. +7 OR Why does fluorine not show disproportionation reaction? 28. Discuss the concept of hybridisation and describe hybridisation in the case of PCl5 and SF6.The axial bond are longer as compared to equatorial bonds in PCl5 whereas in SF6 both axial bonds and equatorial bonds have the same bond length. Explain. OR  What is formal charge? Find the formal charge of following underline elements in the given molecules:- (a) H2SO4 (b) PO4 -3 (c) NO-3 29. What are the conditions for aromaticity? Find the following compounds that they are aromatic, anti- aromatic and non- aromatic: OR Explain the following terms :- (a) Pyrolysis or cracking (b) Free radical halogenation of alkane (c) β – elimination reaction (dehydrohalogenation of alkyl halide ) 29. (i) Define ionization enthalpy and electron gain enthalpy. (ii)The position of three elements A, B and C in the modern periodic table is as follows : a) Write formula of compound formed between: (i) B and A (ii) B and C b) Is any of the three elements a metal? Give reason to justify your answer. (Section D) (long answer type questions each carry 4 marks) 30. Read the passage given below and answer the following questions. Predicting the Direction of the Reaction- The equilibrium constant helps in predicting the direction in which a given reaction will proceed at any stage. For this purpose, we calculate the reaction quotient Q. The reaction quotient, Q (Qc with molar concentrations and QP with partial pressures) is defined in the same way as the equilibrium constant Kc except that the concentrations in Qc are not necessarily equilibrium values. For a general reaction: aA+bB ⇌cC+dD Qc = [C]c [D]d / [A]a [B]b Then, If Qc > Kc , the reaction will proceed in the direction of reactants (reverse reaction). If Qc < Kc , the reaction will proceed in the direction of the products (forward reaction). If Qc = Kc , the reaction mixture is already at equilibrium. Consider the gaseous reaction of H 2 with I2 , H2 (g) + I2 (g) ⇌ 2HI(g); Kc = 57.0 at 700 K. Suppose we have molar concentrations [H2 ]t =0.10M, [I2 ]t = 0.20 M and [HI]t = 0.40 M. (the subscript t on the concentration symbols means that the concentrations were measured at some arbitrary time t, not necessarily at equilibrium). Thus, the reaction quotient, Qc at this stage of the reaction is given by, Qc = [HI]t 2 / [H2 ] t [I2 ] t = (0.40)2/ (0.10)×(0.20) = 8.0 Now, in this case, Qc (8.0) does not equal Kc (57.0), so the mixture of H2 (g), I2 (g) and HI(g) is not at equilibrium; that is, more H2 (g) and I 2 (g) will react to form more HI(g) and their concentrations will decrease till Qc = Kc. The reaction quotient, Qc is useful in predicting the direction of reaction by comparing the values of Qc and Kc.Thus, we can make the following generalisations concerning the direction of the reaction If Qc < Kc , net reaction goes from left to right If Qc > Kc , net reaction goes from right to left. If Qc = Kc , no net reaction occurs. Calculating Equilibrium Concentrations In case of a problem in which we know the initial concentrations but do not know any of the equilibrium concentrations, the following three steps shall be followed: Step 1) Write the balanced equation for the reaction. Step 2) Under the balanced equation, make a table that lists for each substance involved in the reaction: (a) the initial concentration, (b) the change in concentration on going to equilibrium, and (c) the equilibrium concentration. In constructing the table, define x as the concentration (mol/L) of one of the substances that reacts on going to equilibrium, then use the stoichiometry of the reaction to determine the concentrations of the other substances in terms of x. Step 3) Substitute the equilibrium concentrations into the equilibrium equation for the reaction and solve for x. If you are to solve a quadratic equation choose the mathematical solution that makes chemical sense. Step 4) Calculate the equilibrium concentrations from the calculated value of x. Step 5) Check your results by substituting them into the equilibrium equation. Relationship between equilibrium constant K, reaction quotient Q and gibbs energy G The value of Kc for a reaction does not depend on the rate of the reaction. However, it is directly related to the thermodynamics of the reaction and in particular, to the change in Gibbs energy, ∆G. If, ∆G is negative, then the reaction is spontaneous and proceeds in the forward direction. ∆G is positive, then reaction is considered non-spontaneous. Instead, as reverse reaction would have a negative ∆G, the products of the forward reaction shall be converted to the reactants. ∆G is 0, reaction has achieved equilibrium; at this point, there is no longer any free energy left to drive the reaction. A mathematical expression of this thermodynamic view of equilibrium can be described by the following equation: ∆G = ∆Gø + RT lnQ where, Gø is standard Gibbs energy. At equilibrium, when ∆G = 0 and Q = Kc , the equation becomes, ∆G = Gø + RTlnK = 0 ∆Gø = – RT lnK lnK = – ∆Gø / RT Taking antilog of both sides, we get, K = e–∆G0/RT Hence, using the equation , the reaction spontaneity can be interpreted in terms of the value of ∆ G ø. If ∆ Gø < 0, then –∆Gø /RT is positive, and >1, making K >1, which implies a spontaneous reaction or the reaction which proceeds in the forward direction to such an extent that the products are present predominantly. If ∆Gø > 0, then –∆Gø /RT is negative, and < 1, that is , K < 1, which implies a non-spontaneous reaction or a reaction which proceeds in the forward direction to such a small degree that only a very minute quantity of product is formed. Factors affecting equilibria One of the principal goals of chemical synthesis is to maximise the conversion of the reactants to products while minimizing the expenditure of energy. This implies maximum yield of products at mild temperature and pressure conditions. If it does not happen, then the experimental conditions need to be adjusted. For example, in the Haber process for the synthesis of ammonia from N2 and H2 , the choice of experimental conditions is of real economic importance. Annual world production of ammonia is about hundred million tones, primarily for use as fertilizers. Equilibrium constant, Kc is independent of initial concentrations. But if a system at equilibrium is subjected to a change in the concentration of one or more of the reacting substances, then the system is no longer at equilibrium; and net reaction takes place in some direction until the system returns to equilibrium once again. Similarly, a change in temperature or pressure of the system may also alter the equilibrium. In order to decide what course the reaction adopts and make a qualitative prediction about the effect of a change in conditions on equilibrium we use Le Chatelier’s principle. It states that a change in any of the factors that determine the equilibrium conditions of a system will cause the system to change in such a manner so as to reduce or to counteract the effect of the change. This is applicable to all physical and chemical equilibria. Effect of Concentration Change In general, when equilibrium is disturbed by the addition/removal of any reactant/ products, Le Chatelier’s principle predicts that: The concentration stress of an added reactant/product is relieved by net reaction in the direction that consumes the added substance. The concentration stress of a removed reactant/product is relieved by net reaction in the direction that replenishes the removed substance. or in other words, “When the concentration of any of the reactants or products in a reaction at equilibrium is changed, the composition of the equilibrium mixture changes so as to minimize the effect of concentration changes”. Let us take the reaction, H2 (g) + I2 (g) ⇌ 2HI(g) If H2 is added to the reaction mixture at equilibrium, then the equilibrium of the reaction is disturbed. In order to restore it, the reaction proceeds in a direction wherein H 2 is consumed, i.e., more of H2 and I2 react to form HI and finally the equilibrium shifts in right (forward) direction. This is in accordance with the Le Chatelier’s principle which implies that in case of addition of a reactant/product, a new equilibrium will be set up in which the concentration of the reactant/product should be less than what it was after the  addition but more than what it was in the original mixture. The same point can be explained in terms of the reaction quotient, Qc , Qc = [HI]2 / [H2 ][I2] Addition of hydrogen at equilibrium results in value of Qc being less than Kc. Thus, in order to attain equilibrium again reaction moves in the forward direction. Similarly, we can say that removal of a product also boosts the forward reaction and increases the concentration of the products and this has great commercial application in cases of reactions, where the product is a gas or a volatile substance. In case of manufacture of ammonia, ammonia is liquified and removed from the reaction mixture so that reaction keeps moving in forward direction. Similarly, in the large scale production of CaO (used as important building material) from CaCO3 , constant removal of CO2 from the kiln drives the reaction to completion. It should be remembered that continuous removal of a product maintains Qc at a value less than Kc and reaction continues to move in the forward direction.  Assertion and Reason Questions Directions : Each of these questions contain two statements, Assertion and Reason. Each of these questions also has four alternative choices, only one of which is the correct answer. You have to select one of the codes (a), (b), (c) and (d) given below. (a) Assertion is correct, reason is correct; reason is a correct explanation for assertion. (b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion (c) Assertion is correct, reason is incorrect (d) Assertion is incorrect, reason is correct. 1. Assertion : Kp  Kc for all reaction. Reason : At constant temperature, the pressure of the gas is proportional to its concentration. 2. Assertion : If Qc (reaction quotient)  KC (equilibrium constant) reaction moves in direction of reactants. Reason : Reaction quotient is defined in the same way as equilibrium constant at any stage of he reaction. 3. Assertion : According to Le-Chatelier's principle addition of heat to an equilibrium solid ⇌ liquid results in decrease in the amount of solid. Reason : Reaction is endothermic, so on heating forward reaction is favoured 4. Assertion : Equilibrium constant for the reverse reaction is the inverse of the equilibrium constant for the reaction in the forward direction. Reason : Equilibrium constant depends upon the way in which the reaction is written  31. Read the passage given below and answer the following questions:- The first concrete explanation for the phenomenon of the blackbody radiation was given by Max Planck in 1900.An ideal body, which emits and absorbs radiations of all frequencies uniformly, is called a black body and the radiation emitted by such a body is called black body radiation. Max Planck arrived at a satisfactory relationship by making an assumption that absorption and emission of radiation arises from oscillator i.e., atoms in the wall of black body. He suggested that atoms and molecules could emit or absorb energy only in discrete quantities and not in a continuous manner. He gave the name quantum to the smallest quantity of energy that can be emitted or absorbed in the form of electromagnetic radiation. The energy (E ) of a quantum of radiation is proportional to its frequency (ν ) and is expressed by equation E = hv. The proportionality constant, ‘h’ is known as Planck’s constant and has the value6.626×10 - 34 Js.In 1887, H. Hertz performed a very interesting experiment in which electrons (or electric current) were ejected when certain metals (for example potassium, rubidium, caesium etc.) were exposed to a beam of light. The phenomenon is called Photoelectric effect. The results observed in this experiment were: (i) The electrons are ejected from the metal surface as soon as the beam of light strikes the surface, i.e., there is no time lag between the striking of light beam and the ejection of electrons from the metal surface. (ii) The number of electrons ejected is proportional to the intensity or brightness of light. (iii) For each metal, there is a characteristic minimum frequency,ν0(also known as threshold frequency) below which photoelectric effect is not observed. At a frequency ν >ν0, the ejected electrons come out with certain kinetic energy. The kinetic energies of these electrons increase with the increase of frequency of the light used. The particle nature of light posed a dilemma for scientists. The only way to resolve the dilemma was to accept the idea that light possesses both particle and wave-like properties, i.e., light has dual behaviour. Depending on the experiment, wefind that light behaves either as a wave or as a stream of particles. Whenever radiation interacts with matter, it displays particle like properties in contrast to the wavelike properties (interference and diffraction), whichit exhibits when it propagates. This concept was totally alien to the way the scientists thought about matter and radiation and it tookthem a long time to become convinced of its validity. The study of emission or absorption spectra is referred to as spectroscopy. The emission spectra of atoms in the gas phase, on the other hand, do not show a continuous spread of wavelength from red to violet, rather they emit light only at specific wavelengths with dark spaces between them.Such spectra are called line spectra or atomic spectra. The Swedish spectroscopist, Johannes Rydberg, noted that all series of lines in the hydrogen spectrum could be described by the following expression : The value 109,677 cm–1 is called the Rydberg constant for hydrogen. The first five series of lines that correspond to n1= 1, 2, 3,4, 5 are known as Lyman, Balmer, Paschen ,Bracket and Pfund series, respectively. Neils Bohr (1913) was the first to explain quantitatively the general features of the structure of hydrogen atom and its spectrum. He used Planck’s concept of quantisation of energy. Though the theory is not the modern quantum mechanics, it can still be used to rationalize many points in the atomic structure and spectra. Bohr’s model for hydrogen atomis based on the following postulates: i) The electron in the hydrogen atom can move around the nucleus in a circular pathof fixed radius and energy. These paths are called orbits, stationary states or allowed energy states. These orbits are arranged concentrically around the nucleus. ii) The energy of an electron in the orbit does not change with time. However, the electron will move from a lower stationary state to a higher stationary state when required amount of energy is absorbed by the electron or energy is emitted when electron moves from higher stationary state to lower stationary state. The energy change does not take place in a continuous manner. iii) The frequency of radiation absorbed or emitted when transition occurs between two stationary states that differ in energy by ∆E, is given by: Where E1 and E2 are the energies of the lower and higher allowed energy states respectively. This expression is commonly known as Bohr’s frequency rule. iv) The angular momentum of an electron is quantised. In a given stationary state itcan be expressed as in equation  Assertion and Reason Questions Directions : Each of these questions contain two statements, Assertion and Reason. Each of these questions also has four alternative choices, only one of which is the correct answer. You have to select one of the codes (a), (b), (c) and (d) given below. (a) Assertion is correct, reason is correct; reason is a correct explanation for assertion. (b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion (c) Assertion is correct, reason is incorrect (d) Assertion is incorrect, reason is correct. 1. Assertion (A): Black body is an ideal body that emits and absorbs radiation of all frequencies. Reason (R): The frequency of radiation emitted by a body goes from a lower frequency to a higher frequency with an increase in temperature. 2. Assertion: The radius of the first orbit of hy drogen atom is 0.529Å. Reason : Radius for each circular orbit (rn )  0.529Å ( n2 / Z ) , where n  1 ,2,3 and Z = atomic number 3. Assertion : emitted radiation will fall in visible range when an electron jumps from n = 4 to n = 2 in H – atom. Reason : Balmer series radiation belong to visible range for hydrogen atom only. 4. Assertion : according to Bohr’s model of an atom, qualitatively the magnitude of velocity of electron increases with decrease in positive charges on the nucleus as there is no strong hold on the electron by the nucleus.. Reason : according to Bohr’s model of an atom, qualitatively the magnitude of velocity of electron increases with decrease in principal quantum number.  (Section E) (long answer type questions each carry 5 marks) 32. Answer the following questions :- (a) Derive the relation between Kc and Kp. (b) What are the characteristics of equilibrium constant (Kc or Kp) ? (c) Find the pH of a solution obtained by mixing 50 ml of 1 M HCl and 30 ml of 1 M NaOH. 33. Answer the following questions :- (a) Draw the resonating structure of (i) CO2-2 (ii) SO4-2 (b) The order of decreasing stability of the following cations is: (I) CH3C+ HCH3 (II) CH3C+ HOCH3 (III) CH3C+ HCOCH3 (c) Explain Nucleophile and Electrophile. OR st (a) Derive relationship between ∆U = ∆q + ∆W ( 1 law of thermodynamic) (b) Calculate the maximum work obtained when 0.75 mol of an ideal gas expands isothermally and reversible at 27°C from a volume of 15 L to 25 L. (c) Define :- (i) Standard enthalpy of formation. (ii) Standard enthalpy of combustion 34. Answer the following questions :- (a) 45.4 L of dinitrogen reacted with 22.7 L of dioxygen and 45.4 L of nitrous oxide was formed. The reaction is given below: 2N2(g) + O2(g) → 2N2O(g) Which law is being obeyed in this experiment? Write the statement of the law. (b) What is the molarity of a solution that was prepared by dissolving 82.0 g of CaCl2 (molar mass = 111.1 g/mol) in enough water to make 812 mL of solution? (c) 23 g of ethyl alcohol (molar mass 46 g mol-1) is dissolved in 54 g of water (molar mass 18 g mol-1). Calculate the mole fraction of ethyl alcohol and water in solution.