Chemistry
- At 298 K, the standard electrode potentials of Cu^2+/Cu, Zn^2+/Zn, Fe^2+/Fe and Ag^+/Ag are 0.34 V, -0.76 V, -0.44 V and 0.80 V, respectively.On the basis of standard electrode potential, predict which of the following reaction can not occur ? Answer: 1. 2CuSO₄(aq) + 2Ag(s) → 2Cu(s) + Ag₂SO₄(aq) Key idea: a metal can displace another metal from its salt only if its standard reducti... 1
- What mass of 95% pure CaCO_3 will be required to neutralise 50 mL of 0.5 M HCl solution according to the following reaction ?CaCO_3(s) + 2HCl_(aq) → CaCl_2(aq) + CO_2(g) + 2H_2O_(l)[Calculate upto second place of decimal point] Answer: 3. 1.32 g Key idea: find moles of HCl, use the 1 : 2 stoichiometry, then correct for purity. Moles of HCl =0.5×0.050=0.025 mol. CaCO... 1
- Which statement regarding polymers is not correct ? Answer: 1. Thermosetting polymers are reusable. Key idea: thermosetting polymers are cross-linked and cannot be remoulded. Thermosetting pol... 1
- The RBC deficiency is deficiency disease of : Answer: 1. Vitamin B₁₂ Key idea: vitamin mathrmB₁₂ is needed for red blood cell formation. Its deficiency causes pernicious anaemia (reduced... 1
- Which of the following molecules is non-polar in nature ? Answer: 3. SbCl₅ Key idea: a molecule is non-polar if its bond dipoles cancel by symmetry. SbCl₅ is a symmetric trigonal bipyramid with no l... 1
- The slope of Arrhenius Plot ( k v/s 1/T) of first order reaction is -5×10^3 K. The value of E_a of the reaction is. Choose the correct option for your answer.[Given R=8.314 J K^-1mol^-1] Answer: 1. 41.5 kJ mol ⁻¹ Key idea: Arrhenius equation ln k=ln A-E_a/RT ; slope of ln k vs 1/T is -E_a/R . E_a=-slope× R=5×10³×8.314=41570\... 1
- For irreversible expansion of an ideal gas under isothermal condition, the correct option is : Answer: 3. Δ U=0, Δ S_total≠0 Key idea: for an ideal gas, internal energy depends only on temperature. Isothermal means Δ U=0 . An irreversi... 1
- From the following pairs of ions which one is not an iso-electronic pair ? Answer: 4. Fe²⁺, Mn²⁺ Key idea: iso-electronic species have the same number of electrons. mathrmO²⁻ (10) and F^- (10): yes Na^+ (10) and mat... 1
- In which one of the following arrangements the given sequence is not strictly according to the properties indicated against it ? Answer: 2. H₂O < H₂S < H₂Se < H₂Te : Increasing pK_a values Key idea: check each trend. 1: acidic strength HF < HCl < HBr < HI is correct (w... 1
- Match List - I with List - II.List - I : (a) [Fe(CN)_6]^3- (b) [Fe(H_2O)_6]^3+ (c) [Fe(CN)_6]^4- (d) [Fe(H_2O)_6]^2+List - II : (i) 5.92 BM (ii) 0 BM (iii) 4.90 BM (iv) 1.73 BMChoose the correct answer from the options given below. Answer: 4. (a)-(iv), (b)-(i), (c)-(ii), (d)-(iii) Key idea: find unpaired electrons n and use μ=√(n(n+2)) BM. (a) mathrm[Fe(CN)₆]³⁻ : mathrm... 1
- The incorrect statement among the following is : Answer: 2. Most of the trivalent Lanthanoid ions are colorless in the solid state. Key idea: compare f-block properties. Actinoid contractio... 1
- CH_3CH_2COO^-Na^+ [Heat]NaOH,\ +\ ? CH_3CH_3 + Na_2CO_3.Consider the above reaction and identify the missing reagent/chemical. Answer: 3. CaO Key idea: decarboxylation of a sodium carboxylate with soda lime. mathrmCH₃CH₂COONa+NaOHxrightarrowCaO,\ ΔCH₃CH₃+Na₂CO₃ . The... 1
- The reagent 'R' in the given sequence of chemical reaction is :2,4,6-tribromoaniline NaNO_2, HCl,\ 0-5^° C 2,4,6-tribromobenzenediazonium chloride R 1,3,5-tribromobenzene Answer: 2. CH₃CH₂OH Key idea: replacing the diazonium group by hydrogen (hydro-de-diazoniation) needs a mild reducing agent. Ethanol (or H₃P... 1
- The product formed in the following chemical reaction is :2-(methyl-substituted) cyclohexanone bearing CH_2-C(=O)-OCH_3 and CH_3 groups [C_2H_5OH]NaBH_4 ? Answer: 4. Cyclohexane ring with OH, CH₃ and CH₂-C(=O)-OCH₃ substituents Key idea: NaBH₄ is a mild reducing agent. It reduces aldehydes and... 1
- The intermediate compound 'X' in the following chemical reaction is :toluene + CrO_2Cl_2 CS_2 X H_3O^+ benzaldehyde Answer: 1. C₆H₅-CH(OCrOHCl₂)₂ Key idea: this is the Etard reaction: toluene is partially oxidised to benzaldehyde by chromyl chloride. Tolue... 1
- Match List - I with List - II.List - I : (a) benzene [Anhyd. AlCl_3/CuCl]CO,\ HCl (b) R-CO-CH_3 + NaOX → (c) R-CH_2-OH + R'COOH Conc. H_2SO_4 (d) R-CH_2COOH [(ii) H_2O](i) X_2/Red PList - II : (i) Hell-Volhard-Zelinsky reaction (ii) Gattermann-Koch r… Answer: 4. (a)-(ii), (b)-(iii), (c)-(iv), (d)-(i) Key idea: match each reaction with its name. (a) benzene + CO, HCl, anhydrous AlCl₃ /CuCl:... 1
- The molar conductivity of 0.007 M acetic acid is 20 S cm^2 mol^-1. What is the dissociation constant of acetic acid ? Choose the correct option.^°_H^+ = 350 S cm^2 mol^-1, ^°_CH_3COO^- = 50 S cm^2 mol^-1 Answer: 3. 1.75×10⁻⁵ mol L ⁻¹ Key idea: α=Lambda_m/Lambda^°_m , and K_a=Cα²/1-α≈ Cα² . Lambda^°=350+50=400 ; α=20/400=0.05 . K_a≈0.007×(0.05... 1
- The correct option for the value of vapour pressure of a solution at 45^° C with benzene to octane in molar ratio 3 : 2 is :[At 45^° C vapour pressure of benzene is 280 mm Hg and that of octane is 420 mm Hg. Assume Ideal gas] Answer: 3. 336 mm of Hg Key idea: Raoult's law for an ideal solution: P=x₁P₁^°+x₂P₂^° . x_benzene=3/5=0.6 , x_octane=2/5=0.4 . P=0.6(280)+0.... 1
- Tritium, a radioactive isotope of hydrogen, emits which of the following particles ? Answer: 1. Beta ( β^- ) Key idea: tritium ( ³₁H ) is a beta emitter. ³₁H→³₂He+β^-+barν : a neutron changes into a proton, emitting a β^- par... 1
- Choose the correct option for the total pressure (in atm.) in a mixture of 4 g O_2 and 2 g H_2 confined in a total volume of one litre at 0^° C is :[Given R=0.082 L atm mol^-1K^-1, T=273 K] Answer: 3. 25.18 Key idea: PV=nRT with total moles of gas. n_(O_2)=4/32=0.125 ; n_(H_2)=2/2=1 ; total = 1.125 mol. P=nRT/V=1.125×0.082×273/1... 1
- Match List - I with List - II.List - I : (a) 2SO_2(g) + O_2(g) → 2SO_3(g) (b) HOCl(g) h OH + Cl (c) CaCO_3 + H_2SO_4 → CaSO_4 + H_2O + CO_2 (d) NO_2(g) h NO(g) + O(g)List - II : (i) Acid rain (ii) Smog (iii) Ozone depletion (iv) Tropospheric pollutio… Answer: 3. (a)-(iv), (b)-(iii), (c)-(i), (d)-(ii) Key idea: identify each reaction with its environmental context. (a) SO₂ oxidised to SO₃ i... 1
- A particular station of All India Radio, New Delhi, broadcasts on a frequency of 1,368 kHz (kilohertz). The wavelength of the electromagnetic radiation emitted by the transmitter is : [speed of light, c=3.0×10^8 ms^-1] Answer: 1. 219.3 m Key idea: λ=c/ν . ν=1368\ kHz=1.368×10⁶\ mathrms⁻¹ λ=3.0×10⁸/1.368×10⁶=219.3\ m . 1
- Given below are two statements :Statement I : Aspirin and Paracetamol belong to the class of narcotic analgesics.Statement II : Morphine and Heroin are non-narcotic analgesics.In the light of the above statements, choose the correct answer from the o… Answer: 2. Both Statement I and Statement II are false. Key idea: aspirin and paracetamol are non-narcotic analgesics; morphine and heroin a... 1
- Right option for the number of tetrahedral and octahedral voids in hexagonal primitive unit cell are : Answer: 4. 12, 6 Key idea: in a close-packed structure with n atoms per cell, there are n octahedral voids and 2n tetrahedral voids. A hexag... 1