#hsc 12th
- Write two similarities and two differences between lanthanoids and actinoids. Answer: Similarities: Both show a predominant oxidation state of +3. Both involve filling of f-orbitals (4f for lanthanoids, 5f for actinoid... 1
- What is the action of following reagents on chlorobenzene? (i) conc. HNO3 (ii) fuming H2SO4 Answer: (i) Nitration gives 1-chloro-4-nitrobenzene (major) and 1-chloro-2-nitrobenzene (minor). (ii) Sulfonation gives 4-chlorobenzenesulfo... 1
- Explain Cannizzaro reaction with suitable example. Answer: Aldehydes that have no α-hydrogen atom, when heated with concentrated aqueous (or alcoholic) NaOH or KOH, undergo self oxidation–red... 1
- A chemical reaction occurs in two steps :(i) NO2Cl(g) —(slow)→ NO2(g) + Cl(g)(ii) NO2Cl(g) + Cl(g) —(fast)→ NO2(g) + Cl2(g)(a) Write down the rate law.(b) Identify the reaction intermediate. Answer: (a) Rate = k[NO₂Cl] (b) Cl (atomic chlorine) Overall reaction (adding the steps): 2NO₂Cl_((g)) → 2NO_(2(g)) + Cl_(2(g)). (a) The rat... 1
- The standard potential of electrode Cu++ (0.02 M) | Cu(s) is 0.337 volt. Calculate its potential in volt. Answer: E ≈ 0.287 V Electrode reaction: Cu ²⁺ + 2e ^- → Cu(s), n = 2 . Nernst equation at 298 K: E = E^° - 0.0592/nlog₁₀frac1[Cu²⁺] = 0.337... 1
- Derive relationship between relative lowering of vapour pressure and molar mass of non volatile solute.(ii) Write statement of second law of thermodynamics. Answer: (i) P₁^° - P₁/P₁^° = W₂ M₁/M₂ W₁ , so M₂ = W₂ M₁ P₁^°/W₁ (P₁^° - P₁) . (ii) Statement below. (i) By Raoult’s law, for a solution of... 1
- Convert, acetamide into ethyl amine.(ii) Explain amphoteric nature of water. Answer: (i) Acetamide is reduced by lithium aluminium hydride in dry ether, followed by hydrolysis; the C=O group becomes CH₂ and the carbon... 1
- Convert the following :(i) Ethanol into sodium ethoxide.(ii) Phenol into o-phenol sulfonic acid.(iii) Bromomethane into methoxyethane. Answer: (i) Ethanol reacts with sodium metal, liberating hydrogen: 2C₂H₅OH + 2Na → 2C₂H₅ONa (sodium ethoxide) + H₂↑ (ii) Phenol is sulfonate... 1
- What is peptide linkage?(ii) Write general characteristics of interhalogen compounds. Answer: (i) Peptide linkage: The amide linkage –CO–NH– formed between the –COOH group of one α-amino acid and the –NH₂ group of another, wit... 1
- Write observed electronic configuration of chromium (Z = 24).(ii) Calculate magnetic moment of Ti3+ by using spin only formula. (Z of Ti = 22)(iii) Define Green chemistry. Answer: (i) [Ar] 3d⁵ 4s¹ (ii) 1.73 B.M. (iii) Definition below. (i) Cr (Z = 24): 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ 4s¹. The expected 3d⁴4s² is not obs... 1
- Write examples of coordination metal complexes in biology.(ii) Calculate the work done in oxidation of 2 moles of SO2 at 298K, if SO2(g) + ½ O2(g) → SO3(g) [ Given : R = 8.314 J/K/mol ] Answer: (i) Chlorophyll, haemoglobin, vitamin B₁₂ and others. (ii) W = +2477.6 J ≈ +2.48 kJ (work is done on the system). (i) Examples of me... 1
- The carbonated water is an example of _____. Answer: C. gas in liquid solution Answer: (c) gas in liquid solution Carbonated water (soda water) is carbon dioxide gas (solute) dissolved... 1
- The electrolyte used in H2 – O2 fuel cell is _____. Answer: B. aqueous KOH Answer: (b) aqueous KOH In the hydrogen–oxygen fuel cell, hydrogen and oxygen are bubbled through porous carbon elect... 1
- The oxidation state of bromine in HOBrO2 oxoacid is _____. Answer: B. + 5 Answer: (b) +5 HOBrO₂ is bromic acid, HBrO₃. Let the oxidation state of Br be x : (+1) + x + 3(-2) = 0 ⇒ x = +5 . 1
- Acetonitrile may be prepared by heating the following reactants : Answer: C. Methyl chloride with alcoholic KCN Answer: (c) Methyl chloride with alcoholic KCN Acetonitrile is CH₃CN (two carbons), so the alk... 1
- The unit of rate constant is per second, the order of reaction is – Answer: B. First Answer: (b) First Units of k are (mol dm ⁻³ ) ¹⁻ⁿ s ⁻¹ . For n = 1 this becomes s ⁻¹ . (Zero order: mol dm ⁻³ s ⁻¹ ; second... 1
- A system releases 10 kJ of heat and performs 15 kJ of work on the surrounding. Hence the change in internal energy is : Answer: D. – 25 kJ Answer: (d) –25 kJ First law: Δ U = Q + W . Heat released by the system: Q = -10 kJ. Work done by the system on the surro... 1
- The co-ordination complex ions [Co(NH3)5(NO2)]2⊕ and [Co(NH3)5(ONO)]2⊕ are _____ of each other. Answer: C. linkage isomers Answer: (c) linkage isomers NO₂⁻ is an ambidentate ligand. In the first ion it binds to cobalt through nitrogen (... 1
- A coaxial cable consists of a central conducting core wire of radius ‘a’ and a coaxial cylindrical outer conductor of radius ‘b’. The two conductors carry equal current in opposite directions, in and out of the plane of the paper. What will be the ma… Answer: (i) B = μ₀ I/2π r , along circles concentric with the cable (tangential), sense given by the right-hand rule for the core current. (... 1
- Energy of an electron in second Bohr orbit is –3.4 eV. Calculate its kinetic energy and potential energy in third Bohr orbit. Answer: In the third orbit, K.E. ≈ +1.51 eV and P.E. ≈ -3.02 eV. Energy in the n th orbit E_n ∝ 1/n² , so E₃ = E₂ × 2²/3² = -3.4 × 4/9 ≈ -1.... 1
- Derive Laplace’s law for spherical membrane of bubble due to surface tension. Answer: For a soap bubble (two surfaces) the excess pressure inside is P_i - P_o = 4T/R ; for a single spherical surface such as a liquid dr... 1
- Obtain an expression for maximum safety speed with which a vehicle should move along a curved horizontal road.Moment of intertia of a solid sphere about its diameter is 25 kg m\(^2\). Calculate its moment of inertia about a tangent. Answer: v_(max) = √(μ_s r g) ; moment of inertia about a tangent = 87.5 kg m ² . (i) Maximum safety speed on a flat (horizontal) curved road... 1
- Derive the relation between coefficient of absorption, coefficient of reflection and coefficient of transmission.Compare the r.m.s. speed of hydrogen molecule at 127ºC with r.m.s. speed of oxygen molecule at 27ºC, given that molecular masses of hydro… Answer: a + r + t = 1 ; v_(H_2) : v_(O_2) = 8 : √(3) ≈ 4.62 : 1 . (i) Relation: Let Q be the total radiant energy (heat) incident on a body... 1
- Define : (i) Self inductance (ii) Mutual inductanceA conducting loop of area 1 m\(^2\) is placed normal to a uniform magnetic field of 3 Wb/m\(^2\). If the magnetic field is uniformly reduced to 1 Wb/m\(^2\) in 0.5 second, calculate the induced e.m.f… Answer: Definitions below; induced e.m.f. = 4 V. (i) Self inductance: The magnetic flux linked with a coil is proportional to the current in... 1