#hsc 12th
- Draw the structure of 2, 4 – dinitrophenylhydrazone of acetaldehyde.(ii) The rate of A + B → P is 3.6 × 10−2 mol/dm3/s. When [A] = 0.2 M and [B] = 0.1 M. Calculate the rate constant if reaction is first order in B and second order in A. Answer: (i) CH₃–CH=N–NH–C₆H₃(NO₂)₂ (ii) k = 9 dm ⁶ mol ⁻² s ⁻¹ (i) Acetaldehyde condenses with 2,4-dinitrophenylhydrazine (2,4-DNP) with los... 1
- Define : (a) Isotonic solution (b) Molecularity of reaction(ii) State and explain Hess’s law of constant heat summation. Answer: (i)(a) Isotonic solutions: Two or more solutions having the same osmotic pressure at the same temperature are called isotonic soluti... 1
- Define : (a) Schottky defect (b) Ferromagnetism(ii) Write the name of catalyst used in preparation of HDP.(iii) Draw structure of isoprene unit of natural rubber. Answer: (i)(a) Schottky defect: A point defect in an ionic solid in which an equal number of cations and anions are missing from their latti... 1
- Calculate effective atomic number of Fe2⊕ in [Fe(CN)6]4⊖ [ Given : (Z = 26) ](ii) Draw neat and labelled diagram of lead accumulator.(iii) Write two advantages of hydrogen – oxygen fuel cell. Answer: (i) EAN = 36. (ii) Diagram described below. (iii) Advantages below. (i) EAN = (number of electrons in the metal ion) + (number of el... 1
- Convert, ethanoic acid to ethanol.(ii) Explain the mechanism of alkaline hydrolysis of bromomethane. Answer: (i) Ethanoic acid is reduced by lithium aluminium hydride in dry ether, followed by acid hydrolysis: CH₃COOH + 4[H] —(i) LiAlH₄, dry... 1
- Acetic acid is 5% ionised in its decimolar solution. Calculate the dissociation constant of acetic acid.(ii) Write chemical formula of epsom salt. Give two uses of H2SO4. Answer: (i) K_a ≈ 2.5×10⁻⁴ (using K_a = cα² ; the exact expression gives 2.63×10⁻⁴ ). (ii) MgSO₄·7H₂O; uses below. (i) c = 0.1 M (decimolar)... 1
- The pOH of 0.01 M HCl solution is _____. Answer: D. 12 Answer: (d) 12 HCl is a strong acid, so [H₃O^+] = 0.01 = 10⁻² M and pH = 2. At 298 K, pH + pOH = 14, so pOH = 14 − 2 = 12. 1
- Write the name of product obtained, when selenium is treated with magnesium metal. Answer: Magnesium selenide (MgSe). Mg + Se → MgSe (on heating). Group 16 elements combine with metals to form chalcogenides (oxides, sulfide... 1
- Write the SI unit of cell constant. Answer: m⁻¹ (per metre). Cell constant b = l/a (length/area), so its unit is m/m ² = m ⁻¹ . 1
- Write the name of radioactive element in lanthanide series. Answer: Promethium (Pm, Z = 61). Promethium is the only lanthanoid with no stable isotope; all its isotopes are radioactive. 1
- Write the chemical name of Teflon. Answer: Polytetrafluoroethylene (PTFE). It is the addition polymer of tetrafluoroethylene, F₂C=CF₂; repeating unit –[CF₂–CF₂]–. 1
- Write the name of nanoparticle which acts as highly effective bacterial disinfectant. Answer: Silver nanoparticles. Silver nanoparticles are strongly antibacterial and are used in water purification, wound dressings and coatin... 1
- The correct order for basic strength of amines and ammonia is _____. Answer: D. NH3 < R–NH2 < R2NH > R3N Answer: (d) NH₃ < R–NH₂ < R₂NH > R₃N Alkyl groups are electron-releasing (+I effect), so aliphatic amine... 1
- Amongst the following 3d-series elements, having highest value of first ionization enthalpy is _____. Answer: A. Zn Answer: (a) Zn Zinc has the completely filled stable configuration [Ar]3d¹⁰4s², and its 4s electron is held more strongly beca... 1
- Complete the following reaction :Phenol (C6H5OH, a benzene ring carrying an –OH group) + 3 H2 —(Nickel, 433 K)→ ? Answer: Cyclohexanol. C₆H₅OH + 3H₂ —(Ni, 433 K)→ C₆H₁₁OH (cyclohexanol). The benzene ring is fully hydrogenated; the –OH group remains on th... 1
- Write the IUPAC name of :(Structure: a benzene ring carrying a –CHO group, and an –OH group on the adjacent (ortho) carbon.) Answer: 2-Hydroxybenzaldehyde (common name: salicylaldehyde). The –CHO group has the higher priority, so it gives the parent name benzaldehy... 1
- Copper has fcc structure with edge length 495 pm. What is the radius of copper atom in pm? Answer: r ≈ 175 pm In an fcc unit cell atoms touch along the face diagonal: 4r = √(2) a . r = √(2) a/4 = a/2√(2) = 495/2.828 ≈ 175\ pm 1
- Define : (a) Isomorphism (b) Unit Cell Answer: (a) Isomorphism: Two or more substances having the same crystal structure (and similar chemical formula / atomic ratio) are said to... 1
- Explain the trends in the following properties of group 17 elements : (i) Atomic radii (ii) Electronegativity Answer: Down group 17, atomic radii increase (F < Cl < Br < I) and electronegativity decreases (F > Cl > Br > I). (i) Atomic radii: Halogens... 1
- Explain Homoleptic and Heteroleptic complexes with example. Answer: Homoleptic complexes: complexes in which the central metal ion is bonded to only one kind of ligand. Example: [Co(NH₃)₆]³⁺ (only NH₃... 1
- Write the reaction of bromine water on glucose.(b) Define – Enantiomers Answer: (a) Bromine water, a mild oxidising agent, oxidises the –CHO group of glucose to –COOH, giving gluconic acid: CHO–(CHOH)₄–CH₂OH + [O... 1
- Write example of one dimensional nanostructure of size less than 100 nm.(ii) Write the hydrolysis reaction of ethyl methyl ether. Answer: (i) Nanowires, nanorods or nanotubes, e.g. carbon nanotubes (one dimension is long while the other two are below 100 nm). (ii) Ether... 1
- Calculate the osmotic pressure of solution containing 0.822 gm of sucrose in 300 mL of water at 298 K. [ Given : Molar mass of sucrose 342 g/mol, R = 0.08205 dm\(^3\) atm K\(^{-1}\) mol\(^{-1}\) ] Answer: π ≈ 0.196 atm Moles of sucrose n = 0.822/342 = 2.404×10⁻³ mol. Volume V = 300 mL = 0.300 dm ³ (taking the volume of the solution as... 1
- Write the mathematical equation of first law of thermodynamics for following processes : (a) Isochoric process (b) Adiabatic process Answer: (a) Δ U = Q_v (b) Δ U = W First law: Δ U = Q + W , with W = -P_extΔ V . (a) Isochoric process ( Δ V = 0 ): W = 0 , so Δ U = Q_v . Th... 1