Manipur Cohsem Class 11 Chemistry — Real Previous-Year Papers

During photoelectric effect experiment with magnesium metal (work function = 5.8 x 10^-19 J) using radiation of frequency, v = 1.5 x 10¹5 s^-1 the kinetic energy of the emitted electron is - (a) 4.1 x 10^-19 J (b) 2.1 x 10^-19 J (c) 4.1 x 10^-4 J (d) 4.1 x 10^-34 J

A piece of paper is found to be 5.32 cm long and 2.4 cm broad. The area of the paper expressed with proper significant figures is - (a) 12.768 cm² (b) 12.76 cm² (c) 12.8 cm² (d) 13 cm²

Elements "A" and "B" obey Octaves law and have similar properties. Number of elements in between them is - (a) 6 (b) 8 (c) 7 (d) 6 or 13

Which of the following compounds has zero dipole moment? (a) H2S (b) SO2 (c) BCl3 (d) NH3

Which one of the following represents a heterogenous equilibrium? (a) N2(g) + 3H2(g) ⇌ 2NH3(g) (b) N2(g) + O2(g) ⇌ 2NO(g) (c) CH3COOC2H5(aq) + H2O(l) ⇌ CH3COOH(aq) + C2H5OH(aq) (d) CaCO3(s) ⇌ CaO(s) + CO2(g)

Among the structural isomers of hexane, the isomer having highest boiling point is - (a) CH3-C(CH3)2-C2H5 (2,2-dimethylbutane) (b) CH3-CH(CH3)-CH2-CH2-CH3 (2-methylpentane) (c) CH3-CH(CH3)-CH(CH3)-CH3 (2,3-dimethylbutane) (d) CH3-CH2-CH2-CH2-CH2-CH3 (n-hexane)

The IUPAC name of the organic compound (structure shown) is - (a) pent-1, 4- dien-3-one (b) penta-1, 4- dien-3-one (c) pent-1, 4 diene-3-one (d) penta-1, 4- diene-3-one

The oxidation number of chlorine in the molecule KClO3 is - (a) +1 (b) -1 (c) +2 (d) +5

Assertion (A): The melting of ice above 0°C is a spontaneous process. Reason (R): The enthalpy change of the process is negative (-ΔH). (a) Both A and R are true and R is the correct explanation of A. (b) Both A and R are true but R is not the correct explanation of A. (c) A is true but R is false. (d) A is false but R is correct.

Assertion (A): In the displacement reaction M(s) + AgNO3(aq) → M(NO3)2 + 2Ag(s) the metal M acts as reductant. Reason (R): Reduction potential of metal M is lower than that of silver. (a) Both A and R are true and R is the correct explanation of A. (b) Both A and R are true but R is not the correct explanation of A. (c) A is true but R is false. (d) A is false but R is correct.

Illustrate the law of multiple proportion by taking the oxides of sulphur as example.

A2+ is a H like species (Z= 3). Calculate its ionization potential if that of H atom is 13.6 eV.

Classify each of the following redox reactions with respect to the categories: combination reaction, decomposition reaction, combustion reaction, and double displacement reaction. (1+1=2) (i) Cl2(g) + F2(g) → 2ClF(g) (ii) C2H5OH + 3O2 → 2CO2 + 3H2O

A2 is a diatomic molecule. It has a covalent bond formed by overlapping of the atomic orbitals containing one unpair electron each. Draw the potential energy curves of the molecule when the two electrons are of (i) opposite spins (ii) parallel spins.

The dissolutions of anhydrous and hydrated copper sulphate are as follows: CuSO4(s) + aq → CuSO4(aq); Δ = -66.5 kJ mol^-1. CuSO4.5H2O(s) + aq → CuSO4(aq); ΔH = +11.7 kJ mol^-1. Calculate the enthalpy of hydration of copper sulphate CuSO4(s).

Predict the conjugate acid and conjugate base of NH3.

Give an example of a reaction in which a metal displaces a non-metal from its compound. How can you say that it is a redox reaction? (1+1=2)

0.500 g of an organic compound burns in excess O2 to produce 1.25 g of CO2 and 0.613 g of H2O. Calculate the percentage composition of C and H in the compound.

Draw a paper chromatogram showing the separation of two components with different Rf values present in a mixture.

Why is cyclopentadienyl anion aromatic in nature?

Answer either (a) or (b): (a) 100 g of an organic acid sample (molecular mass = 60) contains 39.9 g C, 6.7 g H and 53.4 g O. Determine the molecular formula of the acid. **OR** (b) Precipitation of silver chloride is carried out by adding an excess of 0.5 M NaCl solution to 10 ml of 1.0 M AgNO3 solution. Calculate the amount of silver chloride precipitated in the reaction (Atomic mass of silver = 108).

State Modern periodic law. How does atomic size vary along the period and group? (1+1+1=3)

Find out the bond orders and compare the bond strengths for N2+ and N2-.

Derive the relationship between Kp and Kc for a general reaction represented as aA + bB ⇌ cC + dD in which all reactants and products are gases.

Answer either (a) or (b): (a) Balance the following redox reaction in acidic medium by ion-electron method. Zn(s) + NO3-(aq) → Zn2+(aq) + NH4+(aq) **OR** (b) The standard electrode potentials of two half cells M1(2+)/M1 and M2(2+)/M2 are found to be -0.76 V and +0.34 V respectively. Which one of the two will be used to construct a galvanic cell in which hydrogen electrode functions as anode? Write the half-cell reactions. (1+1+1=3)

Case-study: In organic reactions, the organic molecule reacts with an appropriate attacking reagent and leads to the formation of one or more intermediate(s) and finally product(s). It is important to explain how the products of the reaction are formed and this explanation takes the form of a reaction mechanism. The movement of electrons in the mechanism of the organic reactions can be shown by curved-arrow notations. In the mechanism, covalent bond cleavages may take place either in heterolytic way or homolytic way. Reagents that attack the reactive site of the substrate may be either electrophile or nucleophile in nature. The reagent attacks on the basis of polarization of the substrate molecule. There are some important factors that contribute to the polarization of the covalent bonds. The electron displacements like inductive effect, hyperconjugation and resonance cause permanent polarization of the bond while electromeric effect causes temporary electron displacement effects. The degree of polarization due to these electron displacement effects decide the nature of reactions and the reactivity of the substrate molecules. Write answer of either (a) or (b): (a) Use curve arrow notation to show resonance and use the electron displacement factor to explain how the benzene ring of aniline, C6H5NH2 becomes more reactive towards electrophiles. (2+1=3) **OR** (b) Using hyperconjugation and inductive effect factors, explain why the addition of H+ to propene CH3-CH=CH2 takes place preferably at C-1. Show the attack of the reagent using curve arrow notation. (2+1=3)

Answer either (a) or (b): (a) What is the difference between orbit and orbital? For sodium atom identify the set of quantum numbers for the orbital of the valence electron. If the electron has a de Broglie wavelength of 225 nm calculate its speed. (2+1+2=5) **OR** (b) Distinguish between an emission spectrum and an absorption spectrum? Why is the energy of an electron in Bohr's orbit negative? Calculate the frequency of light emitted when the electron in a hydrogen atom undergoes a transition from energy level n = 4 to level n = 2? (2+1+2=5)

Answer either (a) or (b): (a) Define thermodynamic system and surroundings? Classify the systems into different types. (1+1+3=5) **OR** (b) State the three laws of thermodynamics. How can energy changes associated with chemical or physical processes be experimentally measured? (1+1+1+2=5)

Answer either (a) or (b): (a) (A), C4H6 is an acidic unsaturated hydrocarbon which can form monosodium salt with sodium metal. On reduction with Lindlar's catalyst, A forms compound B which on ozonolysis gives two products C and D. Identify A, B, C, D and write the sequence of reactions. (1+1+1+1+1=5) **OR** (b) "A" is an organic compound formed when sodium salt of benzoic acid is heated with soda lime. Compound A on reaction with CH3Cl / anhydrous AlCl3 gives compound B which on treatment with Cl2 in the presence of UV light gives a monochloro derivative C. Identify A, B, C and write the sequence of the reactions. What is the named reaction involved in the conversion of A to B. (1+1+1+1+1=5)